characterisation proteolytic enzyme to rat man - gut.bmj.com · gut, 1984, 25, 656-664...

Gut, 1984, 25, 656-664

Characterisation of a novel proteolytic enzyme localisedto goblet cells in rat and manE NEX0, S S POULSEN, S N HANSEN, P KIRKEGAARD, AND P S OLSEN

From the Department of Clinical Chemistry ML and Department of Surgery C, Rigshospitalet, Copenhagen,Anatomy Department B and The Protein Laboratory, University of Copenhagen, Denmark

SUMMARY A proteolytic enzyme, ingobsin, purified from rat duodenal extracts is shown to belocalised to intestinal goblet cells of both man and rat. Enzyme positive cells decrease in numberfrom duodenum to colon. The enzyme is a 33 000 Mr protein with an isoelectric point of 5. 1. ThepH optimum for enzymatic activity is 7-4-8-0. Based on substrate specificity for arg-x, lys-x and toa lesser degree tyr-x, on the effect of diisopropylphosphorofluoride, Trasylol and phenylmethyl-sulfonylfluoride and on proteolytic activity towards intact proteins, ingobsin is classified as a

serine proteinase with endoproteolytic activity.

Large amounts of goblet cells are localised in thesurface epithelium of the intestinal mucosa. Theirmain function is the production of mucus which is ofimportance for a normal intestinal function.'During the isolation of duodenal epidermal

growth factor2 we concomitantly purified an enzymethat proved to be localised to the goblet cells. Thepresent paper presents data on the purification,characterisation, and localisation of this hithertounknown enzyme.

Methods

MATERIALSPurification procedureDuodena were removed from Wistar rats underether anaesthesia and kept frozen until used. For atypical purification procedure 25 duodena - that is,approximately 25 g tissue - were homogenised in100 ml acetic acid, 50 mmol/l. After freeze thawingpH was adjusted to 4-5 and the solution wascentrifuged 10 minutes, 20 000 rpm at 4°C. Theprecipitate was washed twice with 50 ml acetic acid,50 mmolIl. The combined supernatants were filteredthrough glasswool, lyophilised, and redissolved in 70ml hydrochloric acid 50 mmol/l, sodium chloride0-15 mol/l, pH 1-5. After centrifugation for 30minutes, 20 000 rpm at 4°C, the supernatant waslyophilised, redissolved in 8 ml distilled water, andpH was adjusted to 1-5. The sample was applied onAddress for correspondence: Ebba Nexo, Clin Chem Dept, Central Hospital,DK3400 Hillerod, Denmark.Received for publication 12 August 1983

a 20x 1100 mm Plo Biogel (BioRad, Richmond,California, USA) column run at 14*5 ml/h withhydrochloric acid 50 mmol/l, sodium chloride 0.15mol/l, pH 1-5. Fractions of 2.9 ml were collected.The enzyme containing fractions were pooled,dialysed against distilled water, lyophilised,redissolved in 3-5 ml imidazole 0.025 mmol/lchromatofocusing buffer (Pharmacia A/S, Uppsala,Sweden), and pH adjusted to 7*4. The sample wassubjected to chromatofocusing on a 9x 135 mm (8ml) column (Pharmacia A/S) and run with a pHgradient from 7-4 to 4. The flow rate was 26 ml/h andfractions of 1 ml were collected. The enzymecontaining fractions were pooled, dialysed,lyophilised, and redissolved in 1 ml of water. pH wasadjusted to 8*0, and the sample was filtered througha 10x450 mm G-75 Sephadex (Pharmacia A/S,Uppsala, Sweden) column run with ammoniumbicarbonate 1 mol/l, pH 8-0, at a flow rate of 5.5ml/h. Fractions of 1 1 ml were collected. Theenzyme containing fractions were lyophilised andkept at -20°C until used for further studies.

Production of antibodyA rabbit was given approximately 30 ,ug (1 nmol)enzyme (300 ,ul) mixed with an equal volume ofFreunds complete adjuvant (Behringwerke,Marburg, FRG) by multiple intradermal injectionson the back. Three booster injections were given attwo week intervals by injecting approximately 30 ,ug(1 nmol) of enzyme mixed with incomplete Freundsadjuvant (Behringwerke, Marburg, FRG). Anti-serum was obtained by aortic puncture.

656

on 16 February 2019 by guest. P

rotected by copyright.http://gut.bm

j.com/

Gut: first published as 10.1136/gut.25.6.656 on 1 June 1984. D

ownloaded from

http://gut.bmj.com/

Goblet cell proteolytic enzyme

Immunohistochemical studiesRat duodenum, jejunum, ileum, colon,submandibular gland, trachea, pancreas, liver,kidney, and stomach were obtained from Wistarrats. A human duodenal specimen was obtainedfrom a patient undergoing Billroth I partialgastrectomy. The tissues were fixed at room

temperature in Bouin's fixative by immersion for 24hours, dehydrated, and embedded in paraffin.The enzyme was localised by the unlabelled

antibody peroxidaseantiperoxidase (PAP)technique.3 The primary antiserum was used atdilutions of 1/100 and 1/400. In controls, the primary

specific antibody was replaced by non-immunerabbit serum or by antiserum preincubated with theenzyme.

Stokes radiusStokes radius was calculated based on data obtainedby G-200 Sephadex (Pharmacia A/S), Dextran blueand 22Na were used as markers for void and totalvolume. Human albumin was used as internalcalibration (Stokes radius 3*6 nm).4

Sodium dodecyl sulphate (SDS) polyacrylamide gelelectrophoresisFifteen or 12i% continuous gels or 9-20% dis-continuous gels were run as described5 on samplesreduced by heating to 100°C in the presence ofdithiothreitol.

lodinated samples were exposed for 24 hours.Gels with 3HDFP labelled samples (see below) wereincubated with Enhance NEF 966 (NEN, Boston,USA) and exposed for two weeks at -20°C. Theplates used were Kodak XL-1 (Roskilde, DK).

Immunoblotting of the separated polypeptideswas performed as described6 on nitrocelluloseAAHY 304 FO (Millipore, Bedford, USA). Theprotein bands were visualised by incubation withantibody or non-immune serum 1:100 overnightafter two hours incubation with peroxidase labelledswine anti-rabbit immunoglobulin 1:1000 (DAKO,Copenhagen, DK). A colour reaction wasdeveloped by approximately 10 minutes incubationwith 3-amino-9-ethyl-carbazole (Sigma, St Louis,USA).

Isoelectric focusingIsolectric focusing was carried out as described bythe manufacturer on a LKB equipment (Bromma,Sweden) using a pH gradient from 3-5 to 9.5. Thegel was cut into 5 mm pieces, the enzyme was elutedovernight in 500 ul phosphate buffer and tested as

described below.

Amino acid analysisAmino acid analysis was performed on 15 ,ug protein

hydrolysed for 24 hours7 using a DurrumD 500 amino acid analyser. Reagents used for thisprocedure were from Dionex (Sunnyvale,California, USA) analytical grade.

Test for enzymatic activityThe enzyme cleaved 251I-EGF so that it could nolonger be precipitated by thrichloracetic acid.Approximately 100 000 cpm 1251 mouse EGF2 wasincubated for one hour at room temperature with100 ,AI sample, mixed with 300 ,lA buffer andprecipitated with 1 ml 20% trichloracetic acid (v/v)for 10 minutes on ice. After centrifugation for 20minutes at 3000 rpm, the enzyme activity wasexpressed as the fraction of 1251 remaining in thesupernatant. The buffer was phosphate 0.1 mol/l,sodium chloride 0-15 mol/l, 0O1% human albumin(Behringwerke, Marburg, FRG), pH 7-4. Forquantification of the enzyme, a calibration curveranging from 0.05 to 1 ,ug/ml (1.5-33 nmol/l)purified enzyme dissolved in testbuffer wasincluded. Buffers for determination of the pHoptimum were hydrochloric acid or phosphatebuffers8 containing sodium chloride 0.15 mol/l and0*1% albumin (Behringwerke).

Enzymatic activity towards synthetic substratesThis was determined essentially as described.9 Inbrief, 10 IlI (1 ,ug) (33 pmol) enzyme was added to500 ul substrate, 0*25 mmol/l dissolved in buffer(sodium phosphate 0-1 mol/l, EDTA 75 umol/l, pH8-0). The change in absorbance at 246, 250, or 255nm, depending on the substrate, was recorded on aUnicam spectrophotometer.The following substrates and enzymes were

obtained from Sigma (St Louis, USA): N-alpha-benzoyl-L-alanine-methylester, N-alpha-benzoyl-L-arginine-ethylester, N-benzoyl-L-tyrosine-ethylester, N-alpha-p-tosyl-arginine-methylester, N-alpha-p-tosyl-L-lysine-methylester, N-benzoyl-glycine-arginine, alpha-chymotrypsin (EC 3.4.21.1),elastase (EC 3.4.21.11), and phenylmethylsulfonyl-fluoride. Trasylol 20 000 KIU/ml was from Bayer(Leverkausen, FRG). Trypsin TPCK (EC 3.4.21.4)was obtained from Worthington (Freehold, NewJersey, USA) and submandibular protease wasobtained from Boehringer Mannheim, (FRG).

IodinationThis was performed using the chloramin T method.In brief, approximately 0-2 nmol (6 jug) of proteindissolved in 200 ul 0X2 mol/l phosphate buffer, pH7.6, was iodinated with 1 mCi 25I (Amersham, UK)by vigorous mixing with 20 ,ul chloramin T (0-25mg/ml) (Merck, USA) for 40 seconds. Iodinationwas terminated by addition of 20 ,lA sodium

657



j.com/


ownloaded from

http://gut.bmj.com/

Nex0, Poulsen, Hansen, Kirkegaard, and Olsen

bisulphite (Merck, USA) (0.5 mg/ml) and vigorousmixing for 15 seconds. After addition of 1 ml 0 1mol/l phosphate, 0.15 mol/l sodium chloride, 0*1%albumin free and protein bound iodine wasseparated by dialysis against phosphate bufferovernight or by gel filtration on G-75 Sephadex asdescribed above.

Labelling of enzymeLabelling of enzyme with (1,3-H3) Di-isopropylphosphorofluoridate, 6 Ci/mmol (3HDFP)(Amersham, UK). Approximately 33 ,ug enzyme (1nmol) dissolved in 500 ,ul 0.1 mol/l phosphate, 0.15mol/l sodium chloride, 01% albumin, pH 8, wasincubated with 20 nmol 3HDFP for eight hours atroom temperature and at 4°C overnight, in thepresence or absence of 50 KIU Trasylol. As apositive control, bovine trypsin approximately 2nmol was labelled in a similar manner.

Digestion of native proteinsThis was assessed using human albumin (Behring-werke, Marburg, FRG), and three cobalaminbinding proteins purified as previously described'((human intrinsic factor, rabbit transcobalamin andhuman haptocorrin). Approximately 40 Ag ofprotein (0.7-1 nmol) dissolved in 50 ,ul ammoniumbicarbonate 0 1 mol/l, pH 80, was digested with 0 4,ug (12 pmol) enzyme for 18 hours at 37°C. Forbinding studies, 0.25 pmol of haptocorrin or intrinsicfactor was mixed with approximately equal amountsof 57Co-cyanocobalamin (Amersham, UK) adjustedto a specific activity of 0. 1 ,uCi/pmol with cyano-cobalamin (Dumex, Copenhagen, DK). Afterincubation overnight at room temperature aliquotsof 50 ul were incubated for three hours at roomtemperature with 25 ul of the test solution. Thebuffer was sodium phosphate 0-1 mol/l, sodiumchloride 0-15 mol/l, human albumin 0-1%, pH 80.In a second set of experiments, the enzymaticdigestion was performed before incubation with thelabelled cobalamin. Free and protein boundcobalamin were separated by charcoal precipita-tion." To compare digestion of native and heatdenatured (100°C for 10 minutes) protein, hapto-corrin was iodinated as described above. Digestion125I haptocorrin, of 1251 insulin (Novo, Copenhagen,DK), and 125I EGF was performed as described forthe cobalamin labelled proteins. Digested peptide(protein) was estimated by calculation of theamounts of 125I remaining in the supernatant afterprecipitation with trichloroacetic acid in a finalconcentration of 13%.

Concentration of proteinsThis was estimated by the method of Lowry.'2

Human albumin (Behringwerke, Marburg, FRG)was used as calibrator.

Immunoprecipitation of enzymeThis was performed using swine anti-rabbit gamma-globulin (DAKO, Copenhagen, DK). Thirty threepicomoles (1 ug) enzyme was mixed with 10 ,ulantiserum incubated for one hour at roomtemperature in a total volume of 1 ml phosphatebuffer; 100 ,ul second antibody was then added andthe samples were incubated overnight at 4°C.Antibody precipitated material was collected afterthree times washing with 0 1 mol/l phosphate, 015mol/l sodium chloride, and centrifugation at 20 000g for 30 minutes between each washing. Controlsamples were incubated with non-immune seruminstead of antiserum.

Results

An enzymatic activity from rat duodenal extractshas been purified by combining gel chromatographyand chromatofocusing (Fig. 1). Approximately 33nmol (1 mg) of enzyme could be purified from 50 gof starting material - that is, 50 duodena. Thisrepresents a yield of around 20%. The enzymeeluted with a KD of approximately 0-6 at Biogel P(,,pH 1.5, and not as expected from its molecular sizewith a KD close to zero. A similar retention of PI(Biogel has been described and used for thepurification of epidermal growth factor.13

Stokes radius estimated by G-200 Sephadex gelfiltration of the enzyme was 1-9 nm. In accordancewith this SDS-polyacrylamide gel electrophoresis ofunlabelled enzyme, iodinated enzyme, or 3HDFPlabelled enzyme showed one band with a relativemolecular mass of 33 000. The same band was seenby Western blotting (Fig. 2). The much weakerbands sometimes seen by SDS electrophoresis hadlower relative molecular masses and varied frompreparation to preparation. These are most likelycreated by autodigestion. Carbohydrates could notbe detected by either carbohydrate staining of thegels or by amino acid analysis.Amino acid analysis of two different preparations

gave almost identical results (Table I). It showed ahigh content of acidic amino acids in accordancewith the rather low isoelectric point of 5*1 asdetermined by isoelectric focusing (Fig. 3).The antibody reacted with the enzyme thought it

did not block the enzymatic reactivity. Thus,enzymatic reactivity was recovered in theprecipitate, when the enzyme was incubated withantiserum followed by second antibody. Noenzymatic reactivity was found when non-immuneserum was employed instead of antiserum.

658



j.com/


ownloaded from

http://gut.bmj.com/


Fig. 1 Purification of ratintestinal goblet cell enzyme,ingobsin, from duodenalextracts. Solid line indicatesOD 280, dotted line indicatesenzymatic activity towardsepidermal growth factor.Upper: P,o-Biogelchromatography. Middle:Chromatofocusing offraction50 to 85from P,o-Biogelchromatography. *--indicates pH. Lower: G-75Sephadex chromatography offraction 75 to 90fromchromatofocusing pooled withsimilarfractions from anotherchromatofocusing column.Fraction 22 to 31 was usedforfurther study.

I

014

00

m

:3

l<

0

-106 0-0 8

-06

0-4

-O 2

By immunohistochemical procedures, the enzymewas localised to some of the goblet cells induodenum from both rat and man (Fig. 4). Thereactive cells were concentrated in the epithelium ofthe crypts and in the lower part of the villi. Theirnumber decreased towards colon, where very fewpositive cells were detected. Also the cells of thegranular convoluted tubules in the submandibularglands of the rat showed a weak positive reaction(data not shown). In contrast all other tissuesexamined were negative. These include gastricmucosa, tracheal mucosa, pancreas, liver, andkidney.By enzymatic assay, the enzyme was found in

amounts of 50 to 300 ,g (1 .5-9 nmol) per ratduodenum and from less than 10-100 ug (less than0*3-3 nmol) in duodenal juice collected over fivehours through a catheter placed in a duodenal pouchin a way that prevented contamination with sputumand pancreatic juice.'4The purified enzyme was able to digest a number

of synthetic substrates as well as native peptides andproteins. The enzymatic activity could be blocked

completely by Trasylol (500 KIU/ml) (Fig. 3) and byphenylmethylsulfonylfluoride. The latter blocked50% of the activity towards benzoyl-arginine-ethylester in a concentration of 2*5 mmol/l. Theenzyme also bound 3HDFP as seen in Figure 2.The enzyme proved active towards lys-x, arg-x,

and to a lesser degree towards tyr-x. No activitytowards ala-x and gly-x was observed (Table 2).Enzymatic activity towards intact peptides was

found for insulin (data not shown) and epidermalgrowth factor. Though the latter peptide wascleaved so that it could no longer be precipitated bytrichloroacetic acid nor be recognised by itsreceptor, the antigenicity and relative molecularmass as judged by gel filtration was unchanged.2These findings suggest the enzyme reacts only onamino acid no 45 (arg-asp5or/and 48 (arg-trp) of this53 amino acid peptide. 5 The pH optimum forcleavage of epidermal growth factor was 7.4 to 8 0.and the activity of the enzyme towards this peptidewas about eight times the activity of trypsinexpressed on a molar basis (Fig. 5). Though theenzyme was inactive at pH below 3, the low pH of

659



j.com/


ownloaded from

http://gut.bmj.com/


Table 1 Molecular characteristics of rat intestinal goblet cell enzvme, ingobsin, and selected other enzymes

Ingobsin EGF binding Trqpsin Chvnotrypsitl Entterokinase(rat)* protein (nouse)t (bovine)* (bovine)* (human)§

Asp 38-34 28 22 19 163thr 1.-13 15 It( 22 89scr 26-25 14 34 21 99glu 30-26 21 14 18 129pro "-" 15 8 13 93glv 34-33 23 5 23 117ala 27-25 14 14 23 711/2cvs -10 8 12 1( 24val 16- 11 17 25 74mct -3 3 2 4 8ile 16-14 7 15 9 62Icu 24-23 24 14 19 l(O)tvr 10-9 10 10 3 32phe 7-7 7 3 7 58his 6-6 5 3 2 23Ivs 11-13 21 15 11 58.;rg .5-4 4 2 5 35Total 290 230 223 245 1235

Carbohydrate + +P1 5-1 5 6 6.7 7 2 4.0-4.9pH optima 7.4-8.0 7.8-835 78 8-X9()9 56-6.2MrxIo3 33 27 24 25 296Localisation Intestinal Submandibulary Pancrcas Pancrcas Intestinal

goblet cclls gland cpithelialsubmandibulary ccllsgland

* This studv. Data from:, ref 9. 19: 25; * 20 and 26.

1-5 used during purification did not destroy theenzymatic activity.The enzyme was able to digest a variety of native

proteins as exemplified in Fig. 6. The pattern ofdigestion was similar to the one of trypsin but it wasnot identical.We examined the activity of the enzyme towards a

cobalamin binding glycoprotein, human hapto-corrin. present in the upper gastrointestinal tract.The protein has to be digested in order to ensurebinding of cobalamin to intrinsic factor prior to itsuptake in the ileum."t The enzyme at a concen-tration between 01 and 1 ,umol/l destroyed thecobalamin binding capacity of both unsaturated andcobalamin saturated haptocorrin. Trypsin did thesame only at a molar concentration 10 times as high(Fig. 5). In contrast neither the enzyme nor trypsinaltered the binding ability of saturated orunsaturated human intrinsic factor. Another featuredistinguished the activity of the purified enzymefrom that of trypsin. While the enzyme (1.5 ,umol/l)digested native and heat denatured haptocorrin atcomparable rates, trypsin (1.5 ,mol/l) digested heatdenatured haptocorrin about four times as fast asnative haptocorrin.

Discussion

We have purified a proteolytic enzyme from ratduodenum, and suggest the name ingobsin becauseof its histochemical localisation to intestinal gobletcells of both rat and man. The localisation issurprising, as to our knowledge no proteolyticenzyme has previously been isolated from the gobletcells. Also the distribution along the intestinal tractis curious. Whereas the goblet cells increase innumber from duodenum over ileum and jejunum tocolon, the number of cells containing enzymeimmunoreactivity are most numerous in theduodenum. The enzyme seems localised to youngcells, as it is most abundant in the lower part of thevilli and in the crypts. This is in contrast with themucus, which is believed to be secreted throughoutthe life span of the goblet cells.'6 17The enzymatic reactivity of ingobsin for the

synthetic substrates lys-x, arg-x, and to a lesserdegree tyr-x, combined with the ability of Trasyloland phenylmethylsulfonylfluoride to inhibit theenzymatic activity, and with the ability of 3HDFP tolabel to the enzyme shows the enzyme to be a serineproteinase as for example, trypsin, chymotrypsin,

660



j.com/


ownloaded from

http://gut.bmj.com/


Fig. 2 SDS polyacrylamide gel ofthe purified enzymeingobsin. (A) 9-20% gradient gel ofreduced samples. Left:marker mix coloured with 0*5% Amidoblack. The markersarefrom top to bottom: phosphorylase B Mr 92 500,albumin M, 67 000, carbonic anhydrase Mr 30 000, andalpha-lactalbumin Mr 14 400. Middle: 10 ,ug (0.3 nmol)enzyme seen by immunoblotting with antiserum 1:100.Right: 10 jig (0 3 nmol) enzyme developed byimmunoblotting with non-immune serum 1:100. (B, C, D)12-5% gel ofreduced samples. (B) Marker mix (left) and 10,ug (0.3 nmol) enzyme (right) stained with cromassie blue.The markers arefrom top to bottom: phosphorylase A, Mr94 000 (6 ,ug); albumin, M,67 000 (8 ug); ovalbumin, Mr43 000 (15 ,ug); carbonic anhydrase, Mr30 000 (8 ug);soybeantrypsin inhibitor, M,20 100 (8 ,ug); and alpha-lactalbumin, Mr 14 400 (12 ,ug). (C) Autoradiogram ofapproximately 10 000 cpm (left) and 100 000 cpm (right)iodinated purified enzyme. (D) Autoradiogram of3HDFPlabelled enzyme in the presence of Trasylol (left) and in theabsence of Trasylol (right). The high molecular band seenin the presence of Trasylol most likely corresponds to anon-specific labelling ofalbumin. An identical band wasseen when labelling trypsin in the presence of Trasylol (datanot shown).

~0-6

>-0 2 V0 2 4. 6 8 10 12 11.

Fraction No

Fig. 3 Isoelectric focusing of rat intestinal goblet cell

enzyme, ingobsin. Solid line indicates enzymatic activity

and dotted line (_+-J.- the pH, the dotted line (O--O--OJindicates the same samples run in the presence of Trasylol.

and submandibular arginine-esterase. Its ability to

cleave proteins at multiple sites further characterises

the enzyme as an endopeptidase.18

Though ingobsin in some respect seems similar to

previously described serine proteinases it is not

identical with any of them. The amino acid

composition compares best with that of the EGF

binding protein, one of the submandibular

191

protelnases, but the isoelectric point, and the

substrate specificity differs.2t) The intestinal

localisation compares with that of enterokinase, but

the relative molecular mass, substrate specificity,and histochemical localisation differs. 21 22 The

substrate specificity is similar ttthat of trypsin, both

concerning activity towards synthetic substrates and

towards intact proteins and peptides. The pattern of

digestion, however, is not identical, the amino acid

composition differs, and the immunohistochemicallocalisation of the two enzymes are different.

Ingobsin is found not only in duodenal extracts,

but also in duodenal juice. Thus the enzyme, like

Table 2 Enzymatic activity of rat intestinal goblet cell enzyme, ingobsin, and selected other enzymes towards syntheticsubstrates

EGFbinding Chymo-Ingobsin* proteint Trypsin* trypsin* Elastase*

Tosyl-L-lysine methylester 100 + + +Tosyl-L-arginine methylester 77 + + +++Benzoyl-L-arginine diethylester 20 + + + +Benzoyl-L-tyrosine ethylester 6 + + +Benzoyl-L-alanine methylester +++Benzoyl-glycine-arginine t

Activity is expressed relative to the activity towards tosyl-L-lysine methylester.* This study. t Data from ref 9. f Indicates no detectable activity.

661



j.com/


ownloaded from

http://gut.bmj.com/


Fig. 4 Histochemical studies of rat intestinal goblet cell enzyme, ingobsin. Rat duodenal mucosa (a, b, and c) and humanduodenal mucosa (d and e) was incubated with anti-rat ingobsin (b, c, and e) and with non-immune serum-(a and d). Themagnification is 210 (a, b) and 850 (c, d, and e).

the mucus of the goblet cell, is delivered by exocrinesecretion.

Ingobsin was discovered because of its ability tocleave the peptide epidermal growth factor even atvery low concentrations. Epidermal growth factor isa 53 amino acid polypeptide that among otherproperties has a protective function on the gastro-intestinal surface epithelium.13 Further, both theintact peptide and the C-terminal shortened 48amino acid peptide inhibits gastric acid secretion.23As ingobsin is most likely to cleave epidermalgrowth factor at the arg residue in position 48, itseems possible that the enzyme cleaves thismitogenic peptide so that it becomes only a gastricacid inhibitory molecule.

At higher though still physiological concen-trations, ingobsin is able to destroy the cobalaminbinding capacity of the endogenous glycoproteinhaptocorrin, although it does not prevent thebinding of cobalamin to intrinsic factor. The normalabsorption of vitamin B12 (cobalamin) depends on atransfer of cobalamin, ingested with the food andbound to saliva or gastric haptocorrin, from hapto-corrin to the transport protein, intrinsic factor.10The physiological mechanism for this is not clarifiedthough it is known that high concentrations oftrypsin in vitro does promote the transfer ofcobalamin from haptocorrin to intrinsic factor.24The present study shows ingobsin to be considerablymore potent than trypsin in destroying the

662



j.com/


ownloaded from

http://gut.bmj.com/

Goblet cell proteolytic enzyme 663

0.9-~~~~~~~~~~~~~~~~~~0097

\, \

0.37

0.1 -(a) (b)

0) 10 1b2 103 104(nmol/ I )

Fig. 5 Proteolytic activity of rat intestinal goblet cellenzyme, ingobsin, as compared with trypsin. (a) Digestionof'251 labelled epidermal growth factor with ingobsin (solidline) and with trypsin (dotted line). (b) Digestion ofsaturated (0) and cobalamin unsaturated (0) humanhaptocorrin with ingobsin (solid line) and with trypsin(dotted line). Abscissa indicates enzyme substanceconcentration, ordinate indicates thefraction ofdigestedpeptide (protein).~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~. _.......~~~~~~~~~~~~~~~~~~~~~~~~~~~.. ... . . _. . . .~~~~~~~~~~~~~~

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.

Fig. 6 15% SDS-polyacrylamide gel electrophoresis ofproteins partly digested with ingobsin (right) or trypsin(left). (A) Rabbit transcobalamin (M 40 000); (B) humanhaptocorrin (M, 70 000); (C) human albumin (Mr 67 000);(D) marker mix (as describedfor Fig. 2).

cobalamin binding capacity of both cobalaminsaturated and cobalamin unsaturated haptocorrin.

The technical assistance of Bente Hansen-Schwartzand Birgit W J0rgensen is warmly acknowledged.This study was supported by grants from the DanishHospital Foundation for Medical Research, Regionof Copenhagen, The Faroe Islands and Greenland(82/33), the NOVO Foundation, and the DanishMedical Research Council (12-1759/81 and 12-3088/82).

References

1 Filipe MI. Mucins in the human gastrointestinalepithelium: a review. Invest Cell Pathol 1979; 2:195-216.

2 Skov Olsen P, Nex0 E. Quantitation of epidermalgrowth factor in the rat. Identification and partialcharacterization of duodenal EGF. Scand J Gastro-enterol 1983; 18: 771-6.

3 Sternberger L. Immunocytochemistry. EnglewoodCliffs, New York: Prentice Hall, 1974: 129-71.

4 Ackers GK. Molecular exclusion and restricteddiffusion processes in molecular-sievechromatography. Biochemistry 1964; 3: 723-30.

5 Farrell PHO. High resolution two dimensional electro-phoresis of proteins. J Biol Chem 1975; 250: 4007-21.

6 Burnette WN. 'Western blotting' electrophoretictransfer of proteins from sodium dodecyl sulfatepolyacrylamide gels to unmodified nitrocellulose andradiographic detection with antibody and radio-iodinated protein A. Anal Biochem 1981; 112: 195-203.

7 Moore S, Stein WH. Chromatographic determinationof amino acids by the use of automatic recordingequipment. In: Colowick SP, Kaplan NO, eds.Methods in enzymology. Vol 6. New York: AcademicPress, 1963: 819-31.

8 Dawson RM, Elliott DC, Elliott WH, Jones KM. Datafor biochemical research. Oxford: Clarendon Press,1978.

9 Taylor JM, Mitchell WM, Cohen S. Characterization ofthe binding protein for epidermal growth factor. J BiolChem 1974; 249: 2188-94.

10 Nex0 E, Olesen H. Intrinsic factor, transcobalamin,and haptocorrin. In: Dolphin D, ed. B,,. Vol 2. 1982:57-85.

11 Lau K, Gottlieb C, Wasserman LR, Herbert V.Measurement of serum vitamin B12 level using radio-isotope dilution and coated charcoal. Blood 1965; 26:202-14.

12 Lowry OH, Rosenbrough WJ, Farr AR, Randall RJ.Protein measurement with the Folin Phenol reagent.J Biol Chem 1951; 193: 265-75.

13 Hollenberg MD. Epidermal growth factor-urogastrone, a polypeptide acquiring hormonal status.Vitam Horm 1979; 37: 69-110.

14 Kirkegaard P, Lundberg JM, Poulsen SS et al.



j.com/


ownloaded from

http://gut.bmj.com/

664 Nex0, Poulsen, Hansen, Kirkegaard, and Olsen

Vasoactive intestinal polypeptidergic nerves andBrunner's gland secretion in the rat. Gastroenterology1981; 81: 872-8.

15 Cohen S, Savage CR Jr. Recent studies on thechemistry and biology of epidermal growth factor.Recent Progr Horm Res 1974; 30: 551-74.

16 Specian RD, Neutra MR. Regulation of intestinalgoblet cell secretion. I. Role of parasympatheticstimulation. Am J Physiol 1982; 242: 370-9.

17 Neutra MR, O'Malley LJ, Specian RD. Regulation ofintestinal goblet cell secretion. II. A survey of potentialsecretagogues. Am J Physiol 1982; 242: 380-7.

18 Stroud R. A family of protein-cutting proteins. Sci Am1974; 231: 74-88.

19 Barka T. Biological active polypeptides in sub-mandibular glands. J Histochem Cytochem 1980; 29:836-59.

20 Server AC, Shooter EM. Comparison of the arginineesteropeptidases associated with the nerve andepidermal growth factors. J Biol Chem 1976; 251:

165-73.21 Grant DAW, Hermon-Taylor J. The purification of

human enterokinase by affinity chromatography andimmunoadsorption. Biochem J 1976; 155: 243-54.

22 Lobley RW. Franks R, Holmes R. Subcellularlocalization of enterokinase in human duodenalmucosa. Clin Sci Mol Med 1977; 53: 551-62.

23 Hollenberg MD, Gregory H. Epidermal growth factor-urogastrone: biological activity and receptor binding ofderivatives. Mol Pharmacol 1980; 17: 314-20.

24 Allen RH, Seetharam B, Podell E, Alpers DH. Effectof proteolytic enzymes on the binding of cobalamin toR protein and intrinsic factor. J Clin Invest 1978; 61:47-54.

25 Dayhoff MO. Atlas of protein sequence and structure.Washington: National Biomedical ResearchFoundation, 1972: 5.

26 Nordstrom C, Dahlquist A. Rat enterokinase: theeffect of ions and the localization in the intestine.Biochem Biophys Acta 1971; 242: 209-25.



j.com/


ownloaded from

http://gut.bmj.com/

characterisation proteolytic enzyme to rat man - gut.bmj.com · gut, 1984, 25, 656-664...

Documents