Biochemistry and physiology of xylose fermentation by yeasts

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<ul><li><p>810chem15try and phy510109y 0f xy105e fermentat10n 6y yea5t5 8. Hahn-Hf19erda1,* H. Jepp550n,* K. 5k009** and 8. A. Pr10r t </p><p>*Department 0f App11ed M1cr0610109Y, Chem1ca1 Centre, Lund 1n5t1tute 0f 7echn0109Y, Lund Un1ver51ty, Lund, 5weden </p><p>**Pre5ent addre55: Chr15t1an Han5en5 La60rat0r1um, 869e A11~ 10-12, 2970 H6r5h01m, Denmark tDepartment 0f M1cr0610109Y and 810chem15try, Un1ver51ty 0f the 0ran9e Free 5tate, 810emf0nte1n, 50uth Afr1ca </p><p>7he rate 0f ethan01 pr0duct10n and the ethan01 c0ncentrat10n5 atta1ned 6y the m05t pr0m151n9 xy105e-ferment1n9 yea5t5, P1ch1a 5t1p1t15, Cand1da 5hehatae, and Pachy501en tann0ph11u5, c0mpare p00r1y w1th that 0f c0mmerc1a1 ethan01fermentat10n 6y n0n-xy105e-ferment1n9 5acchar0myce5 cerev151ae u51n991uc05e-6a5ed 5u65trate5. 7he 0xY9en re4u1rement f0r eff1c1ent fermentat10n 6y the xY105e-ferment1n9 yea5t5 and the 1ack 0f 5uch a 9enera1 re4u1rement 6y 5. cerev151ae 1nd1cate5 6a51c underty1n9 d1fference51n the1r phy5101091ca1 re1at10n5 t0 0xy9en. 7he red0x 1m6a1ance 1n the 1n1t1a1 c0nver510n 0f xy105e t0 xy1u105e, 5en51t1v1ty t0 h19h c0ncentrat10n5 0f ethan01, d1fference5 1n the re5p1rat0ry pathway and 5en51t1v1ty t0 m1cr061a1 1nh161t0r5, part1cu1ar1y th05e 116erated dur1n9 pretreatment and hydr01y515 0f 119n0ce11u105e 5u65trate5, have 6een 1denuf1ed a5 maj0r fact0r511m1t1n9 ethan01fermentat10n 6y the xy105e-ferment1n9 yea5t5. Rec0m61nant 5. cerev151ae, c0nta1n1n9 funct10na1 xy105e reducta5e and xy11t01 dehydr09ena5e, 9r0w5 0n, 6ut p00rty ferment5, xy105e. 7he unfav0ra61e k1net1c pr0pert1e5 0f the5e en2yme5 and an 1nade4uate pent05e ph05phate pathway apparent1y 11m1t the a6111ty 0f the rec0m61nant yea5t t0 ferment xy105e. </p><p>Keyw0rd5: Yea5t5; xy105e fermentat10n; ethan01 pr0duct10n; 0xY9en re1at10n5 </p><p>1ntr0duct10n </p><p>51nce the d15c0very 0f the a6111ty 0f yea5t5 t0 ferment xy105e 1n 1981,1-3 the pathway f0r the meta60115m 0f xy105e ha5 6een exten51ve1y 1nve5t19ated. Wherea5 6acter1a were 5h0wn t0 150mer12e xy105e d1rect1y t0 xy1u105e a5 ear1y a5 1960, Ch1an9 and Kn19ht 4 f0und that the f11ament0u5 fun- 9u5 Pen1c1111um chry509enum p055e55ed en2yme5 f0r the 1n1- t1a1 5tep5 0f pent05e meta60115m that d1ffered fr0m xy105e 150mer12at10n 1n 6acter1a. Yea5t5 5uch a5 Cand1da ut1115, wh1ch are a61e t0 0x1d12e xy105e and 9r0w 0n the 5u65trate, were f0und t0 1n1t1a11y reduce xy105e t0 xy1u105e v1a xy11t01. 5 7hereafter, xy1u105e 15 ph05ph0ry1ated t0 xy1u105e-5- ph05phate. 7h15 1ntermed1ate 15 then meta60112ed 6y the pent05e ph05phate pathway (F19ure 1). Xy105e-ferment1n9 yea5t5 were f0und t0 f0110w the 0x1d0-reduct1ve r0ute v1a xy11t011n the c0nver510n 0fxy105e t0 xy1u105e. 7he 519n1f1cant </p><p>Addre55 repr1nt re4ue5t5 t0 Pr0f. Hahn-H/19erda1 at the Department 0f App11ed M1cr0610109Y, Chem1ca1 Centre, Lund 1n5t1tute 0f 7echn0109y, Lund Un1ver51ty, P. 0.80x 124, 5-221 00 Lund, 5weden 7h15 art1c1e 15 a rev15ed and updated ver510n 0f pa9e5 242-2591n 8. Hahn- H/19erda1, J. Ha1160rn, H. Jepp550n, L. 01550n, K. 5k009, M. Wa1fr1d550n, Pent05e Fermentat10n t0 A1c0h01 1n 810c0nver510n 0f F0re5t and A9r1- cu1tura1P1antRe51due5, Ed. J. N. 5add1er, CA8 1nternat10na1, Wa111n9f0rd, UK, 1993 Rece1ved 13 5eptem6er 1993; accepted 1 Fe6ruary 1994 </p><p>d1fference 6etween hex05e and pent05e meta60115m 15 that a11 pent05e5, c0ntrary t0 hex05e5, 6 have t0 6e 5hutt1ed thr0u9h the PPP. 7he 610techn01091ca11y 1mp0rtant yea5t 5acchar0myce5 cerev151ae 15 una61e t0 ferment xy105e 6ut can ferment xy1u105e, and when the xy105e 150mera5e 15 pre5ent 1n the med1um, xy105e 15 c0nverted t0 xy1u105e wh1ch 15 then fermented t0 ethan01.7he ethan01 f0rmat10n rate 1n xy105e- ferment1n9 yea5t5 when xy105e 15 a551m11ated 15 a60ut ha1f that when 91uc05e 15 a551m11ated. 7-9 C0rre5p0nd1n9 re5u1t5 were 06ta1ned dur1n9 the fermentat10n 0f xy1u105e 6y 5ch1205acchar0myce5 p0m6e 1 and 6y 5. cerev151ae. 11 7h15 rev1ew w111 exam1ne the phy5101091ca1 a5pect5 0f xy105e fer- mentat10n 6y P1ch1a 5t1p1t15, Cand1da 5hehatae, and Pachy- 501en tann0ph11u5, a5 the5e three yea5t5 have 6een m05t exten51ve1y 5tud1ed. 0ther yea5t5 w111 6e referred t0 where appr0pr1ate. </p><p>C0mpar150n 0f the xy105e-ferment1n9 a6111ty 0f yea5t5 </p><p>7he yea5t5 P. 5t1p1t15 and the c105e1y re1ated C. 5hehatae are the 6e5t xy105e-ferment1n9 yea5t5 de5cr16ed t0 date 12 ( 7a61e 1). 1n 9enera1, 5tra1n5 0f the5e yea5t5 pr0duce ethan01 at max1mum 5pec1f1c rate5 up t0 0.51 9 9 -1h- 1 w1th ethan01 y1e1d5 up t0 0.50 9 9-1.13C0mpared w1th P. tann0ph11u5, the5e yea5t5 ferment xy105e up t0 f1ve t1me5 fa5ter w1th a </p><p>13 15 h19her ethan01y1e1d. - Neverthe1e55, the 5pec1f1c ethan01 </p><p> 1994 8utterw0rth-He1nernann En2yme M1Cr06.7eChn01., 1994, V01. 16, N0Vem6er 933 </p></li><li><p>Rev1ew5 </p><p>Xy105e </p><p>Xy105e NADPH- -~NADH NADP + ~ NAD + </p><p>NAD+~Xy11t01 NADH~ </p><p>5u9ar uptake </p><p>NADPH NADP + </p><p>1 6 Ph05ph091uc0nate </p><p>61uc05e </p><p>1 61uc05e </p><p>- 61uc05e 6P </p><p>C02 </p><p>Xy1u105e ~ DP+ ~-- -~7- - - - - - FruCt05e 6P R16u105e ~, </p><p>~5P ~. . . . .. f~" 1" 1 FruCt05e 1,6-d1ph05phate Xy1u105e 5P R1605e 5P / / </p><p>/ / / / ,2~ / / </p><p>5ed0heptu105e 7P 1,2~.-~ -~-1r--~/ / </p><p>~- Erythr05e 41:)/// Fruct0.5e 6P / / </p><p>/ </p><p>Fruct05e 6P --~ 61ycera1dehyde 3P - - -~ Pyruvate </p><p>NAD + NADH </p><p>Re5p1rat0ry cha1n NADH NAD + </p><p>61ycera1dehyde 3P </p><p>~ NAD NADH </p><p>C02 ~ C02 </p><p>Acety1 C0A Aceta1dehyde </p><p>D1hydr0xyacet0ne P </p><p>~ NADH NAD + 61ycer01 3P </p><p>61ycer01 </p><p>Acetate NADH NAD + </p><p>Ethan01 </p><p>F19ure 1 Pr0p05ed pathway f0r the meta60115m 0f xy105e and 91uc05e 1n the xy105e-ferment1n9 yea5t5 </p><p>pr0duct1v1ty 0f the 6e5t 0f the xy105e-ferment1n9 yea5t515 at 1ea5t f1vef01d 10wer than that 06ta1ned w1th 5. cerev151ae when cu1t1vated 0n 91uc05e. 0xy9en ha5 6een 5h0wn t0 6e nece55ary f0r eff1c1ent ethan01 f0rmat10n fr0m xy105e 6y the xy105e-ferment1n9 yea5t5.1,16 Xy11t01 15 the pr1nc1pa1 p01y01 pr0duced dur1n9 xy105e fermentat10n 6y the5e yea5t5. H0w- ever, C. 5hehatae and P. 5t1p1t15 pr0duce c0n51dera61y 10wer am0unt5 0f xy11t01 than th05e 065erved 1n P. tann0ph11u5 fermentat10n5. 8 Un11ke P1ch1a an90ph0rae, 17 the5e yea5t5 are 1ncapa61e 0f pr0duc1n9 ethan01 fr0m xy11t01.61ycer01, ara61t01, and r161t01 are a150 accumu1ated dur1n9 xy105e fer- mentat10n 6y P. 5t1p1t15, C. 5hehatae, and P. tann0ph11u5, 6ut 1n m05t 1n5tance5 the c0ncentrat10n5 are 10wer than that 0f xy11t01. 8 </p><p>Fermentat10n 0f 5u9ar5 0ther than D-xy105e 7he a6111ty 0f xy105e-ferment1n9 yea5t5 t0 ferment 5u9ar5 c0mm0n1y f0und 1n 119n0ce11u1051c 610ma55151mp0rtant 1n the1r p0tent1a1 app11cat10n f0r fue1 pr0duct10n. C. 5hehatae </p><p>18 19 and P. 5t1p1t15 ferment 91uc05e, mann05e, and 9a1act05e. , Ce1106105e 15 fermented 6yP. 5t1p1t15 6ut n0t 6y C. 5hehatae. Ne1ther L-ara61n05e, L-rhamn05e, n0r xy11t01 15 fermented 6y the5e yea5t5. 7M 5tra1n5 0fP. 5t1p1t15 and C. 5hehatae 9r0w 0n the a60ve-ment10ned 5u65trate5 w1th the except10n 0f C. </p><p>5hehatae C85 2779, wh1ch cann0t ut1112e L-rhamn05e. 7he a6111ty 0f 0ther xy105e-ferment1n9 yea5t5 t0 ut1112e 0ther 5u9- ar5 ha5 6een 1e55 exten51ve1y 1nve5t19ated. P. tann0ph11u5 can 9r0w 0n 91uc05e, 9a1act05e, xy105e, and fruct05e 6ut n0t </p><p>20 0n 5ucr05e and 1act05e. 1n add1t10n, P. 5t1p1t15 5tra1n5 C85 5773 and C85 5775 are a61e t0 ferment 1archw00d xy1an d1rect1y t0 ethan01. 21 8eechw00d xy1an 15 1nc0mp1ete1y hy- dr01y2ed, wh1ch 1nd1cate5 that the5e 5tra1n5 d0 n0t pr0duce a c0mp1ete c0mp1ement 0f en2yme5 nece55ary f0r xy1an hydr01y515. </p><p>7ran5p0rt 0f xy105e and 91uc05e P. 5t1p1t15 NRRL Y-7124 and C85 7126 take up 60th xy105e 22,23 and 91uc05e 22,24 6y mean5 0f a pr0t0n 5ymp0rt 22 (7a61e 2). 1n P. 5t1p1t15 C85 7126, there are tw0 uptake 5y5tem5 f0r xy105e, a h19h- and a 10w-aff1n1ty 5y5tem, wherea5 there 15 0n1y 0ne uptake 5y5tem f0r 91uc05e. 22 7he 10w-aff1n1ty 5y5tem 15 5hared 6y xy105e and 91uc05e, wherea5 the h19h-aff1n1ty 5y5tem f0r xy105e 15 n0nc0mpet1t1ve1y 1nh16- 1ted 6y 91uc05e. 7he 10w-aff1n1ty 5y5tem wa5 5u6ject t0 5u6- 5trate ( &gt; 0.2 mM) 1nh161t10n when 91uc05e 6ut n0t xy105e wa5 the 5u65trate. 1n c0ntra5t t0 P. 5t1p1t15, C. 5hehatae C85 2779 ha5 a fac111tated d1ffu510n 5y5tem 1n add1t10n t0 the pr0t0n 5ymp0rt. 25 1n n0n5tarved ce115 0f C. 5hehatae, xy105e </p><p>934 En2yme M1cr06.7echn01., 1994, v01.16, N0vem6er </p></li><li><p>810chem15try and phy510109y 0f xy105e fermentat10n: 8. Hahn-H~9erda1 et a1. </p><p>7a61e 1 Effect 0f 0xY9en 0n ethan01 pr0duct10n and xy11t01 f0rmat10n </p><p>Ethan01 Car60n Ethan01 5pec1f1c Xy11t01 810ma55 50urCe y1e1d a pr0duct1v1ty y1e1d a y1e1d a </p><p>5tra1n (9 1-1) Aerat10n (9 9-1) (9 9-1 h-1) (9 9-1) (9 9-1) Ref. </p><p>P1ch1a 5t1p1t15 C85 6054 X 206 Aer061c 0 0 0 0.33 7 C85 6054 X 506 0xY9en 11m1ted 0.46 0.2 0 0.13 44 C85 6054 X 20 Anaer061c 0.35 0.02 0 0 7 C85 6054 6 206 Aer061c 0 0 NA 0.35 52 C85 6054 6 506 0xY9en 11m1ted 0.33 0.38 NA 0.15 52 C85 6054 6 20 Anaer061c 0.50 0.04 NA 0.04 7 </p><p>C85 7126 X 40 Aer061c 0.18 0.17 0 0.39 8 C85 7126 X 40 0xY9en 11m1ted 0.47 0.2 0.06 0.05 8 C85 7126 X 40 Anaer061c 0.4 0.02 0 0.03 8 </p><p>C85 7126 6 40 Aer061c 0.26 0.17 NA 0.23 8 C85 7126 6 40 0xY9en 11m1ted 0.38 0.28 NA 0.14 8 C85 7126 6 40 Anaer061c 0.33 0.13 NA 0.10 8 </p><p>Cand1da 5hehatae C85 2779 X 40 Aer061c 0.22 0.21 0.04 0.33 8 C85 2779 X 40 0xY9en 11m1ted 0.37 0.32 0.13 0.01 8 C85 2779 X 40 Anaer061c 0.41 0.15 0.18 0.01 8 </p><p>C85 2779 6 40 Aer061c 0.33 0.35 NA 0.21 8 C85 2779 6 40 0xY9en 11m1ted 0.42 0.51 NA 0.03 8 C85 2779 6 40 Anaer061c 0.44 0.29 NA 0.02 8 </p><p>Pachy501en tann0ph11u5 N RR L Y-2460 X 40 Aer061c 0.10 0.04 0.17 0.25 8 NRRL Y-2460 X 40 0xY9en 11m1ted 0.28 0.10 0.30 0.01 8 NRRL Y-2460 X 40 Anaer061c 0.26 0.07 0.30 0.01 8 </p><p>NRRL Y-2460 6 40 Aer061c 0.31 0.38 NA 0.14 8 NRRL Y-2460 6 40 0xY9en 11m1ted 0.43 0.49 NA 0.06 8 NRRL Y-2460 6 40 Anaer061c 0.42 0.18 NA 0.04 8 </p><p>1f86 0101 X 30 Aer061c 0 0 0 0.40 20 1f86 0101 X 25 0xY9en 11m1ted 0.12 0.61 20 1f86 0101 X 27 Anaer061c 0.07 0.85 20 </p><p>a9 9 -1 c0n5umed 5u9ar X, Xy105e; 6, 91uc05e NA, N0t app11ca61e 6C0nt1nu0u5 cu1t1vat10n </p><p>and 91uc05e are tran5p0rted v1a the 5ame fac111tated d1ffu- 510n 5y5tem, wherea5 5tarvat10n re5u1t5 1n the 1nduct10n 0f tw0 5ymp0rt5, 0ne f0r xy105e and the 0ther f0r 91uc05e (7a- 61e 2). 7he tran5p0rt 5y5tem5 0f P. tann0ph11u5 and 0ther xy105e-ferment1n9 yea5t5 have n0t yet 6een 1nve5t19ated. </p><p>L0w- and h19h-aff1n1ty 5y5tem5 w1th Km va1ue5 0f 2.26 and 0.08 mM, re5pect1ve1y, were rep0rted f0r P. 5t1p1t15 C85 7126, 22 wherea5 f0r P. 5t1p1t15 NRRL Y-7124 the c0rre- 5p0nd1n9 va1ue5 were 380 and 0.9 mM 23 (7a61e 2). 7he5e d1fference5 1n k1net1c c0n5tant5 may 6e re1ated t0 5tra1n var1at10n5 and d1fference51n 9r0wth c0nd1t10n5. Neverthe- 1e55,1t 15 apparent that the tran5p0rt 5y5tem5 0fP. 5t1p1t15 are m0re eff1c1ent than th05e 0f C. 5hehatae, and that 91uc05e 15 tran5p0rted m0re eff1c1ent1y than xy105e 1n 60th yea5t5. 1n c0ntra5t, C. ut1115, wh1ch 9r0w5 0n, 6ut fa115 t0 ferment, xY105e, p055e55e5 10w-aff1n1ty (Krn va1ue 0f 67.6 mM) and h19h-aff1n1ty (Km va1ue 0f 1.9 mM) xY105e tran5p0rt 51m11ar t0P. 5//p/t/5. 80th 5y5tem5 appeared t0 6e pr0t0n 5ymp0rt5. 26 </p><p>A1th0u9h 5. cerev151ae 15 una61e t0 9r0w 0n xy105e, 27,28 the 0r9an15m 15 a61e t0 ut1112e xY105e under certa1n c0nd1- t10n5. 29,3 Xy105e tran5p0rt 1n 5. cerev151ae 0ccur5 6y fac111- </p><p>tated tran5p0rt. 31 7w0 tran5p0rt 5y5tem5 f0r 91uc05e, c0n- 515t1n9 0f a 91uc05e-repre55161e, h19h-aff1n1ty 5y5tem and a c0n5t1tut1ve, 10w-aff1n1ty 5y5tem, have 6een de5cr16ed. 32-36 Xy105e 15 apparent1y taken up 6y the5e 5y5tem5, 6ut the aff1n1ty 0f the5e 5y5tem5 15 appr0x1mate1y 200-f01d 10wer than th05e f0r 91uc05e. 37-39 Furtherm0re, 5tarvat10n 1ead5 t01nact1vat10n 0fxy105e tran5p0rt, 6ut th15 can 6e prevented 6y exp05ure t0 xy105e and r1605e. 36 </p><p>A num6er 0f 5tud1e5 u51n9 ]4C-xy105e, 13C-nuc1ear ma9- net1c re50nance (NMR) 5pectr05c0py, 0r the 5pec1f1c xy105e uptake rate 22,4,41 1nd1cate that the rate 0f tran5p0rt may 11m1t the ut1112at10n 0f xy105e 1n aer061c and 0xY9en-11m1ted ce115 0fP. 5t1p1t15 and C. 5hehatae 9r0w1n9 0n xy105e. Under anaer061c c0nd1t10n5, tran5p0rt d0e5 n0t appear t0 6e 11m- 1t1n9 1n P. 5t/p/t/5 6ut rather the 1n1t1a1 tw0 5tep5 0f xy105e meta60115m. 40 1n 5. cerev151ae under aer061c c0nd1t10n5, xy- 105e tran5p0rt 15 apparent1y n0t 11m1t1n9 6ut rather the 1n- trace11u1ar meta6011c 5tep5. 36 0xY9en 15 apparent1y nece5- 5ary f0r the uptake 0f certa1n d15acchar1de51n many yea5t5, a1th0u9h 1t 15 n0t re4u1red f0r 91uc05e tran5p0rt. 42,43 1n a recent 5tudy 0n 0xY9en re4u1rement5 f0r xy105e uptake, 44 </p><p>En2yme M1cr06.7echn01., 1994, v01. 16, N0vem6er 935 </p></li><li><p>Rev1ew5 </p><p>7a61e 2 7ran5p0rt 5y5tem51n xy105e-ferment1n9 yea5t 5tra1n5 </p><p>5tra1n 5u9ar Ce11 5tatu5 Krn (mM) 7ype 0f tran5p0rt Ref. </p><p>P1ch1a 5t1p1t15 NRRL Y-7124 X n5 380 a Act1ve tran5p0rt 23 </p><p>0.96 C85 7126 X n5 2.26 a Pr0t0n 5ymp0rt 22 </p><p>0.086 Pr0t0n 5ymp0rt 22 C85 7126 X 5 1.89 a Pr0t0n 5ymp0rt 22 </p><p>0.066 Pr0t0n 5ymp0rt 22 C85 7126 6 n5 0.73 Pr0t0n 5ymp0rt 22 C85 7126 6 5 0.26 Pr0t0n 5ymp0rt 22 C85 5773 6 5 0.02 Pr0t0n 5ymp0rt 24 </p><p>Cand1da 5hehatae C85 2779 X n5 125 Fac111tated d1ffu510n 25 C85 2779 X 5 1 Pr0t0n 5ymp0rt 25 C85 2779 X 5 125 Fac111tated d1ffu510n 25 </p><p>C85 2779 6 n5 2 Fac111tated d1ffu510n 25 C85 2779 6 5 0.12 Pr0t0n 5ymp0rt 25 </p><p>n5, N0n5tarved ce115; 5, 5tarved ce115 aL0w aff1n1ty 6H19h aff1n1ty X, Xy105e; 6, 91uc05e </p><p>the rat10 6etween uptake under aer061c ver5u5 anaer061c c0nd1t10n5 wa5 h19her f0r aer061ca11y cu1tured ce115 than f0r anaer061ca11y cu1tured ce115,1nd1cat1n9 that 0xY9en 1nduce5 0r act1vate5 a tran5p0rt 5y5tem. </p><p>C0nver510n 0f xy105e t0 xy1u105e-5-ph05phate </p><p>Yea5t5 u5e a tw0-5tep 0x1d0-reduct10n react10n t0 c0nvert xy105e t0 xy1u105e. 7h1515 f0110wed 6y a ph05ph0ry1at10n t0 xy1u105e 5-ph05phate. 7he f1r5t en2yme 1n the pathway 15 an NAD(P)H-dependent xy105e reducta5e (XR) (a1d05e re- ducta5e EC 0f the a1d0/ket0 reducta5e fam11y) wh1ch c0nvert5 xy105e t0 xy11t01. Xy11t01 15 e1ther excreted fr0m the ce11 0r 0x1d12ed t0 xy1u105e 6y an NAD +- dependent xy11t01 dehydr09ena5e (XDH; EC (F19- ur, 1 5 45 47 e ). , - 7he 5u65e4uent ph05ph0ry1at10n 15 cata1y2ed 6y xY1u10k1na5e (EC 5,27,46 </p><p>7he re4u1rement f0r 0xy9en dur1n9 xy105e fermentat10n 15 fre4uent1y a5cr16ed t0 the apparent red0x 1m6a1ance wh1ch deve10p5 dur1n9 anaer061c c0nd1t10n5 due t0 the d1f- ference 1n c0fact0r re4u1rement5 0f the f1r5t tw0 en2yme5. 48,49 7he red0x 1m6a1ance hyp0the515 wa5 6a5ed 0n re5u1t5 fr0m a 5tudy 0fC. ut1115, wh1ch ha5 a xy105e reduc- ta5e and a xy11t01 dehydr09ena5e re4u1r1n9 NADPH and NAD +, re5pect1ve1y. 7h15 re5u1t5 1n an 0verpr0duct10n 0f NADP + and NADH, re5pect1ve1y. Wherea5 NADP + can 6e reduced 6y cyc11n9 v1a fruct05e 6-ph05phate, C. ut1115 cann0t re0x1d12e NADH 1n the a65ence 0f 0xy9en. 7h15 1m6a1ance 15 further ref1ected 6y excret10n 0f the 1nterme- d1ate xy11t01. 1f an externa1 e1ect0n accept0r (acet01n) wa5 added, xy11t01 pr0duct10n wa5 prevented and anaer061c eth- </p><p>48 an01 pr0duct10n 0ccurred. N0 tran5hydr09ena5e (NADH + NADP + </p></li><li><p>810chem15try and phy510109y 0f xy105e fermentat10n: 8. Hahn-H~9erda1 et a1. </p><p>3.0 </p><p>t 6 c 2.5 </p><p>~ 2.0 </p><p>~ 1.5 </p><p>0.0 1 1 1 1 1 1 1 1 1 </p><p>&gt;411 411 182 51 31 11 8 2 </p></li><li><p>Rev1ew5 </p><p>anaer061c c0nd1t10n5 when the 1n0cu1a have 6een 9r0wn 0n xy105e 15 uncerta1n. 0ne p05516111ty c0u1d 6e that NADH f0rmed 1n the c0nver510n 0f xy11t01 t0 x~,1...</p></li></ul>


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