Section 9: Section 9:

Control of MetabolismControl of Metabolism

2. Control via hormones2. Control via hormones

12/9/0512/9/05

How are metabolic pathways regulated?How are metabolic pathways regulated?

4 major control mechanisms4 major control mechanisms

control typecontrol type main featuresmain features

1. [substrate]1. [substrate] concentration of 1 substrate is rate-limitingconcentration of 1 substrate is rate-limiting2. allosterism2. allosterism activity of key (control) enzyme modulatedactivity of key (control) enzyme modulated

noncovalent; covalentnoncovalent; covalent

3. [enzyme]3. [enzyme] concentration of key enzyme varied,concentration of key enzyme varied,usually by controlling its rate of synthesis usually by controlling its rate of synthesis

4. hormones4. hormones intercellular signal factors that regulate & intercellular signal factors that regulate & coordinate intracellular processescoordinate intracellular processes

Control mechanisms 4. hormonesControl mechanisms 4. hormones

pathway/processpathway/process limiting factorlimiting factor activated byactivated by inhibited inhibited byby

glucose uptakeglucose uptake transport proteintransport protein insulininsulin cortisolcortisol(muscle, adipose)(muscle, adipose) (GLUT4) (GLUT4)

amino acid amino acid transporttransport insulininsulin cortisolcortisoluptakeuptake (muscle) (muscle) proteins proteins

glycogenolysisglycogenolysis phosphorylasephosphorylase epiepi (muscle) (muscle) insulininsulinglgnglgn (liver) (liver)

glycogenesisglycogenesis synthasesynthase insulininsulin epiepi (muscle) (muscle)glgnglgn (liver) (liver)

lipolysislipolysis lipaselipase epi, glgnepi, glgn insulininsulinepi = epinephrine; glgn = glucagonepi = epinephrine; glgn = glucagon

11

HormonesHormones act by processes called act by processes called signal transduction cascadessignal transduction cascades

signal is conveyed & amplified by varied types of moleculessignal is conveyed & amplified by varied types of molecules a type of signal factor produced in very small amountsa type of signal factor produced in very small amounts carried in the blood from secretion site to target cellscarried in the blood from secretion site to target cells bind to bind to receptorsreceptors produce a response appropriate to the function of many cells produce a response appropriate to the function of many cells

or the body as a wholeor the body as a whole

Structural types of main metabolic hormonesStructural types of main metabolic hormones

derivatives of amino acidsderivatives of amino acids epinephrine, thyroxineepinephrine, thyroxine

steroidssteroids cortisolcortisol

peptidespeptides insulin, glucagoninsulin, glucagon22

Receptor(s)Receptor(s) target cell protein that:target cell protein that:

binds a signal molecule (ligand)binds a signal molecule (ligand) becomes activatedbecomes activated passes the signal alongpasses the signal along

so as to produce a responseso as to produce a response affinity for ligand affinity for ligand

usually highusually high response usually varies response usually varies

hyperbolicallyhyperbolically with [ligand]with [ligand]sometimes variessometimes varies

sigmoidallysigmoidally saturation behaviorsaturation behavior

0

20

40

60

80

100

0 50 100[ligand] nM

% r

esp

on

se

33

Hormones with intracellular receptorsHormones with intracellular receptors sites of action (location of receptor binding site):sites of action (location of receptor binding site):

intracellularintracellular or or cell-surfacecell-surface (extracellular) (extracellular) "intracellular" hormones"intracellular" hormones

lipophilic or amphiphiliclipophilic or amphiphilic transported in blood bound to plasma proteintransported in blood bound to plasma protein enter cytosol of target cell by diffusionenter cytosol of target cell by diffusion bind to a bind to a receptor proteinreceptor protein the hormone-receptor protein complexthe hormone-receptor protein complex•enters the nucleus enters the nucleus •binds to DNA at a sequence called abinds to DNA at a sequence called ahormone (hormone (oror steroid) response element (HRE steroid) response element (HRE oror SRE) SRE)

•activates transcription of one or more genesactivates transcription of one or more genes44

Hormones: intracellularHormones: intracellular cortisol: cortisol:

main metabolic hormone that main metabolic hormone that acts intracellularly acts intracellularly

major major glucocorticoid*glucocorticoid* in humans in humans transported in plasma transported in plasma

~90% protein-bound~90% protein-bound free hormone diffuses free hormone diffuses

across plasma membraneacross plasma membrane hormone binds to hormone binds to

receptor protein in cytosolreceptor protein in cytosol complex enters nucleuscomplex enters nucleus

glucocorticoid glucocorticoid receptor proteinreceptor protein

OH

O

OH OH

O

cortisol

* [glucose]-regulating adrenal cortex hormones* [glucose]-regulating adrenal cortex hormones

steroid steroid hormonehormone

corticosteroid-corticosteroid-binding globulinbinding globulin

nucleusnucleus

cytosolcytosol++

++

55

Intracellular hormones: nuclear effectsIntracellular hormones: nuclear effects in the nucleus, the complex binds in the nucleus, the complex binds

to DNA at HRE called the to DNA at HRE called the gluco-gluco-corticoid response elementcorticoid response element (GRE) (GRE)

numerous genes activatednumerous genes activatede.g.e.g., for transamination,, for transamination,gluconeogenesis enzymesgluconeogenesis enzymes

receptor's DNA binding domain receptor's DNA binding domain has has recognition helicesrecognition helices that are that arepart of motifs called part of motifs called zinc fingerszinc fingers

numerous other hormones & signal factors exert their effects numerous other hormones & signal factors exert their effects via similar mechanism:via similar mechanism:the other steroid hormonesthe other steroid hormones thyroxine thyroxinevitamin D hormonesvitamin D hormones carotenoids carotenoids

group of receptors called the group of receptors called the nuclear receptor superfamilynuclear receptor superfamily

GREGRE

DNADNA

nucleusnucleus

66

DNA-binding domain of hormone receptorDNA-binding domain of hormone receptor

Stryer, 4 ed., Stryer, 4 ed., Figs. 37-33, 37-34Figs. 37-33, 37-34(cf. 5 ed., Fig. 31.22)(cf. 5 ed., Fig. 31.22)

majormajorgroovegroove

F2

F3

F1

recognition helices of recognition helices of 3 Zn fingers (F1, F2 & F3)3 Zn fingers (F1, F2 & F3)bound to DNAbound to DNA

ds DNA

Zinc finger motif

recognition recognition helixhelix

77

Hormones: cell-surfaceHormones: cell-surface receptor proteinreceptor protein

spans plasma membranespans plasma membrane member of receptor familymember of receptor family

called 7TM* receptorscalled 7TM* receptors hormone binding site hormone binding site

interfaces with extracellular fluidinterfaces with extracellular fluid hormone binds reversibly viahormone binds reversibly via

complementary noncovalentcomplementary noncovalentinteractions (NCIs)interactions (NCIs)

binding activates G protein, binding activates G protein, causing GTP to replace GDPcausing GTP to replace GDPbound to bound to subunit subunit

*seven-TransMembrane-helix *seven-TransMembrane-helix ((see Fig. 15.3see Fig. 15.3))88

from from Fig. 21.14Fig. 21.14

7TM receptor7TM receptorproteinprotein

7TM receptors: 7TM receptors: structure & functionsstructure & functions

seven-transmembrane-helix seven-transmembrane-helix Fig. 15.3Fig. 15.3

Fig. 15.3Fig. 15.3

99

Adenylate cyclase activationAdenylate cyclase activation subunit (Gsubunit (G) dissociates) dissociates

from the other subunits (Gfrom the other subunits (G)) GG diffuses anchored to to diffuses anchored to to

membrane, binds to & membrane, binds to & activates adenylate cyclase activates adenylate cyclase

a small fraction ofa small fraction ofATP is converted toATP is converted tocyclic AMP (cAMP)cyclic AMP (cAMP)

cyclic AMP is called acyclic AMP is called asecond messengersecond messenger(intracellular messenger)(intracellular messenger)

ATP

cAMP + PPi

from from Fig. 21.14Fig. 21.141010

GTP

adenylateadenylatecyclasecyclase

GG

Protein kinase AProtein kinase A cyclic AMP activates protein kinase A cyclic AMP activates protein kinase A

by binding to its inhibitory subunits, by binding to its inhibitory subunits, which dissociate (which dissociate (S9L1slide17S9L1slide17))

catalytic subunit can now catalytic subunit can now phosphorylate phosphorylate target enzymestarget enzymes at specific at specific serser//thr thr side chainsside chains ( (S9L1slide18S9L1slide18))

tissuetissue target enzymetarget enzymeadiposeadipose lipase (lipase (S7L1S7L1))

liver, muscleliver, muscle glycogenglycogen synthase & synthase &phosphorylasephosphorylase kinase ( kinase (S6L2S6L2)) targettarget

enzymeenzyme

ATPATP ADPADP

targettargetenzymeenzyme -P-P

CC

R R

CR R

+ 4 cyclic AMP+ 4 cyclic AMP

allosteric control site

C

1111

Activation of Activation of glycogenolysisglycogenolysis

in liver & muscle, in liver & muscle, activated protein kinase A activated protein kinase A activates phosphorylase activates phosphorylase kinasekinase

activated phosphorylaseactivated phosphorylasekinase activates glycogen kinase activates glycogen phosphorylasephosphorylase

activated phosphorylase activated phosphorylase removes glycogen’s glc units removes glycogen’s glc units as glucose 1-phosphateas glucose 1-phosphate

protein kinase Aprotein kinase A(C subunit)(C subunit)

phosphorylasephosphorylase phosphorylasephosphorylasekinasekinase kinasekinase--PP

glycogenglycogen glycogenglycogenphosphorylasephosphorylase phosphorylasephosphorylase--PP

ATPATP ADP

ATPATP ADPADP

Pi + glycogen (glc)Pi + glycogen (glc)nn

glycogen (glc)glycogen (glc)nn–1–1 + glc 1-phosphate + glc 1-phosphate

glc 6-phosphateglc 6-phosphate

GLYCOLYSISGLYCOLYSIS

1212

Deactivation ofDeactivation ofglycogenesisglycogenesis

glycogen synthase is active glycogen synthase is active in in ununphosphorylated formphosphorylated form

activated protein kinase A activated protein kinase A phosphorylates synthasephosphorylates synthase

phosphorylated synthase phosphorylated synthase is is not not activeactive

result:result:when protein kinase A is active, glycogenesis stoppedwhen protein kinase A is active, glycogenesis stopped

net result of hormone binding is coordinated:net result of hormone binding is coordinated: activation of activation of glycogenolysisglycogenolysis inhibition of inhibition of glycogenesisglycogenesis

proteinproteinkinase Akinase A

glycogenglycogen glycogenglycogensynthasesynthase synthasesynthase--PP

ATPATP ADPADP

UDP-glc + UDP-glc +

glycogen (glc)glycogen (glc)nn

UDP + glycogen (glc)UDP + glycogen (glc)nn+1+1

1313

Cell-surface hormones: reversal of effectsCell-surface hormones: reversal of effects processes activated by hormone binding are reversed byprocesses activated by hormone binding are reversed by

hormone dissociation & degradationhormone dissociation & degradation second messenger destruction by second messenger destruction by phosphodiesterasephosphodiesterase::

cyclic AMP + Hcyclic AMP + H22O → 5'-AMPO → 5'-AMP G protein inactivation:G protein inactivation:

• slow hydrolysis of slow hydrolysis of -subunit-bound GTP to-subunit-bound GTP toGDPGDP• GGGDPGDP subunit then rebinds to subunit then rebinds to subunits subunits

protein phosphatasesprotein phosphatases catalyze removal of phosphoryl catalyze removal of phosphoryl groups (groups (insulin-activated)insulin-activated)

protein-protein-PP + H+ H22O O → → protein + Pprotein + Pii

e.g., glycogen phosphorylase-e.g., glycogen phosphorylase-PP +H +H22O →O →

glycogen phosphorylase (inactive)glycogen phosphorylase (inactive)1414

Summary of glycogen mobilization by hormone-activated signal transduction cascade

100x

10,000x

1000x

Signal amplificationx molecules of hormoneresults in downstream:

Fig. 21.14

15

Summary of Fatty Acid Mobilization (S7L1slide8)Summary of Fatty Acid Mobilization (S7L1slide8)

note that the steps are the same through activation of protein kinase note that the steps are the same through activation of protein kinase 1616

Fig. 22.6

Hormones: cell-surface receptor site via Hormones: cell-surface receptor site via tyrtyr kinase activation kinase activation hormone (insulin) binds at hormone (insulin) binds at

receptor sites on receptor sites on subunits subunits this activates intracellular this activates intracellular

tyrtyr kinase domains kinase domains on on subunits subunits

these domains phosphorylate these domains phosphorylate one anotherone another #1 phosphorylates #2#1 phosphorylates #2 #2 phosphorylates #1#2 phosphorylates #1 cross-phosphorylation cross-phosphorylation

(autophosphorylation)(autophosphorylation)

result:result: these domains’ these domains’ tyrtyr kinase kinase activity is increasedactivity is increased PP

tyrosinetyrosinekinasekinasedomainsdomains

insulin bound to receptorsinsulin bound to receptors

cross-cross-phosphorylationphosphorylation

site site

1 2

plasmamembrane

Lehninger et al., 3rd ed., Fig. 13-6

1717

tyrtyr kinase activity: effects kinase activity: effects activated activated tyrtyr kinase domains kinase domains

phosphorylate intracellular phosphorylate intracellular signal factors signal factors (target proteins)(target proteins)

target proteins cause:target proteins cause: activation of transportactivation of transport

(next slide)(next slide) activation/deactivation of activation/deactivation of

specific pathwaysspecific pathways

(see Table on slide 22)(see Table on slide 22) phosphorylated state slowly phosphorylated state slowly

reversed by specific protein reversed by specific protein phosphatasesphosphatases

PP

PP

TyrTyr

TyrTyr

ADPADP

ATPATP

produces produces intracellularintracellularinsulin effectsinsulin effects

targettargetproteinprotein

PP

1 2

1818

Insulin & Insulin & GLUT4GLUT4 at high [glc],at high [glc],

facilitated facilitated diffusiondiffusionmediated by mediated by GLUT4GLUT4(muscle & (muscle & adipose)adipose)

similar similar mechanismmechanismoperates foroperates fortransport of transport of amino acidsamino acidsinto muscleinto muscle

GLUT4(glucosetransporter)

GLUT4 “stored”in vesicles

insulin binding activates exocytosis

as [insulin], endocytosis removes GLUT4

endo-some

fusion

budding

Lehninger et al.,3rd ed., p. 4141919

Major metabolic hormones: overviewMajor metabolic hormones: overviewhormonehormone sourcesource stimulusstimulus general functiongeneral function

epinephrineepinephrine adrenaladrenal alarmalarm mobilize fuelsmobilize fuelsmedullamedulla (neural)(neural)

glucagonglucagon cells of cells of blood blood maintain bloodmaintain bloodpancreas pancreas [glucose][glucose] [glucose],[glucose], [fatty ac][fatty ac]

cortisolcortisol adrenaladrenal bloodblood maintain bloodmaintain bloodcortexcortex [glucose] [glucose] [glucose] &[glucose] &

(via ACTH)(via ACTH) [fatty acids][fatty acids]

insulininsulin cells of cells of blood blood stim. anabolismstim. anabolismpancreas pancreas [glucose] [glucose] (synthesis,(synthesis,

fuel storage) fuel storage)

2020

Major catabolic hormonesMajor catabolic hormoneshormonehormone molec. mechanismmolec. mechanism targets targets effects effects

epineph-epineph- cell-surfacecell-surface musclemuscle glycogenolysis glycogenolysisrinerine receptorreceptor//cAMPcAMP

glucagon glucagon cell-surfacecell-surface liverliver glycogenolysis glycogenolysis receptorreceptor//cAMPcAMP

cortisolcortisol intracellularintracellular receptorreceptor// transcriptiontranscription

adiposeadipose lipolysis lipolysis

adiposeadipose lipolysis lipolysis

most cellsmost cells protein protein synthesis synthesis

adiposeadipose enzymes for enzymes for lipolysis lipolysis

liverliver enzymes enzymes for aa for aa glcglc

2121

Major anabolic hormone: insulinMajor anabolic hormone: insulinmolec. mechanismmolec. mechanism targetstargets effectseffects

cell-surfacecell-surface musclemuscle amino acids, glc uptake* amino acids, glc uptake* receptorreceptor//

tyrtyrkinasekinaseactivation activation glycogenesis glycogenesis

mostmost protein synthesis protein synthesis cells cells glycogenolysis glycogenolysis gluconeogenesisgluconeogenesis

{* via stimulation of fusion of vesicles containing* via stimulation of fusion of vesicles containing transmembrane GLUT4 with cell membrane transmembrane GLUT4 with cell membrane

adiposeadipose glc uptake*, glc uptake*, lipolysis lipolysis

2222

Control of metabolism: Control of metabolism: fill in the blanksfill in the blanks

FATSFATS GLYCOGENGLYCOGEN PROTEINSPROTEINS

fatty acids+ glycerolfatty acids+ glycerol glucose 6-Pglucose 6-P

pyruvatepyruvate

amino acidsamino acids

acetyl CoAacetyl CoA

KrebsKrebscyclecycle

ee––

COCO22

oxidativeoxidativephosphorylationphosphorylation

CoACoAATP ATP ADP + PADP + Pii

HH22O OO O22

vv

vv

2323

oxaloacetateoxaloacetate

NAD+

Web linksWeb links Peptide hormonesPeptide hormones

Resource on the structure & function of various families of hormones, Resource on the structure & function of various families of hormones, which induce many important signal-transduction cascades. Also included which induce many important signal-transduction cascades. Also included are a summary table of structures and functions, as well as descriptions of are a summary table of structures and functions, as well as descriptions of hormone receptors, second-messenger molecules, & related diseases. hormone receptors, second-messenger molecules, & related diseases.

Medical Biochemistry Page, Terre Haute Cntr for Medical EducationMedical Biochemistry Page, Terre Haute Cntr for Medical Education Steroid hormonesSteroid hormones

Companion to Peptide Hormones site (above), this site covers the Companion to Peptide Hormones site (above), this site covers the important characteristics of steroids such as testosterone and cortisol important characteristics of steroids such as testosterone and cortisol and their role in signal transduction.and their role in signal transduction.

Insulin and DiabetesInsulin and Diabetes This Web site defines and describes the many forms of diabetes, one of This Web site defines and describes the many forms of diabetes, one of the best-known metabolic diseases. It includes a thorough discussion of the best-known metabolic diseases. It includes a thorough discussion of the clinical aspects of the disease, as well as its biochemical and the clinical aspects of the disease, as well as its biochemical and physiological characteristics.Created by Michael King of the Terre Haute physiological characteristics.Created by Michael King of the Terre Haute Center.Center.

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