Oxidoreductases Involved in Cell Carbon Synthesis of Methanobacterium thermoautotrophicum

J. G. Zeikus, G. Fuchs, W. Kenealy, R. K. Thauer
1977 Journal of Bacteriology  
Cell-free extracts of Methai obacteriu mn thermnoautotroph icuni were found to contain high activities of the following oxidoreductases (at 600C): pyruvate dehydrogenase (coenzyme A acetvlating)( 275 nmol/min per mg of protein; itketoglutarate dehydrogenase (coenzyme A acylating). 100 nmol/min per mg; fumarate reductase, 360 nmol/min per mg; malate dehydrogenase. 240 nmol/ min per mg; and glyceraldehyde-3-phosphatp diehydrogenase, 100 nmol/min per mg. The kinetic properties (apparent V"",. and
more » ... apparent V"",. and K, values), pH optimum, temperature dependence of the rate, and specificity for electron acceptors/ donors of the different oxidoreductases were examined. Pyruvate dehydrogenase and (i-ketoglutarate dehydrogenase were shown to be two separate enzymes specific for factor 420 rather than for nicotinamide adenine dinucleotide (NAD), NADP, or ferredoxin as the electron acceptor. Both activities catalyzed the reduction of methyl viologen with the respective ct-ketoacid and a coenzyme Adependent exchange between the carboxyl group of the (t-ketoacid and CO,. The data indicate that the two enzymes are similar to pyruvate synthase and ct-ketoglutarate synthase. respectively. Fumarate reductase was found in the tose phosphate cycle in M. thermoautotrophicum have failed; neither could ribulose-1i5-bisphosphate carboxylase be demonstrated in cellfree extracts, nor was 3-phosphoglycerate de-604 on May 8, 2020 by guest
doi:10.1128/jb.132.2.604-613.1977 fatcat:sm77hrs7wbazbfzi5jwwykqciq