PROPERTIES OF THE 2 ISOENZYMES OF METHYL-COENZYME-M REDUCTASE IN METHANOBACTERIUM-THERMOAUTOTROPHICUM

被引:63
作者
BONACKER, LG
BAUDNER, S
MORSCHEL, E
BOCHER, R
THAUER, RK
机构
[1] MAX PLANCK INST TERR MIKROBIOL,KARL VON FRISCH STR,D-35043 MARBURG,GERMANY
[2] PHILIPS UNIV MARBURG,FACHBEREICHS BIOL,MIKROBIOL LAB,MARBURG,GERMANY
[3] BEHRINGWERKE AG,FORSCHUNGSLAB,W-3550 MARBURG,GERMANY
[4] PHILIPPS UNIV MARBURG,FACHBEREICH BIOL BOT,MARBURG,GERMANY
来源
EUROPEAN JOURNAL OF BIOCHEMISTRY | 1993年 / 217卷 / 02期
关键词
D O I
10.1111/j.1432-1033.1993.tb18281.x
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Methyl-coenzyme M reductase (MCR) catalyses the methane-forming step in the energy metabolism of methanogenic Archaea. It brings about the reduction of methyl-coenzyme M (CH3-S-CoM) by 7-mercaptoheptanoylthreonine phosphate (H-S-HTP). Methanobacterium thermoautotrophicum contains two isoenzymes of MCR, designated MCR I and MCR II, which are expressed differentially under different conditions of growth. These two isoenzymes have been separated, purified and their catalytic and spectroscopic properties determined. Initial-velocity measurements of the two-substrate reaction showed that the kinetic mechanism for both isoenzymes involved ternary-complex formation. Double reciprocal plots of initial rates versus the concentration of either one of the two substrates at different constant concentrations of the other substrate were linear and intersected on the abcissa to the left of the 1/nu axis. The two purified isoenzymes differed in their K(m) values for H-S-HTP and for CH3-S-CoM and in V(max). MCR I displayed a K(m) for H-S-HTP of 0.1 - 0.3 mM, a K(m) for CH3-S-CoM of 0.6-0.8 mM and a V(max) of about 6 mumol . min-1 . mg-1 (most active preparation). MCR II showed a K(m) for H-S-HTP of 0.4-0.6 mM, a K(m) for CH3-S-CoM of 1.3 -1.5 mM and a V(max) of about 21 mumol . min-1 . mg-1 (most active preparation). The pH optimum of MCR I was 7.0-7.5 and that of MCR II 7.5-8.0. Both isoenzymes exhibited very similar temperature activity optima and EPR properties. The location of MCR I and of MCR II within the cell, determined via immunogold labeling, was found to be essentially identical. The possible basis for the existance of MCR isoenzymes in M. thermoautotrophicum is discussed.
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页码:587 / 595
页数:9
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