Intermediary metabolism of Diplococcus glycinophilus. II. Enzymes of the acetategenerating system.

Klein, Sigrid M. (Brigham Young University, Provo, Utah) and Richard D. Sagers. Intermediary metabolism of Diplococcus glycinophilus. II. Enzymes of the acetate-generating system. J. Bacteriol. 83:121-126. 1962-The enzymatic steps in the conversion of glycine to acetate by Diplococcus glycinophilus were examined and the reaction rates of the individual steps compared with the maximal glycine fermentation rate by whole cells. Glycine is oxidatively cleaved to one-carbon units with the alpha carbon being transferred to tetrahydrofolate at the oxidation level of formaldehyde. The activated one-carbon unit is condensed with a second glycine molecule to form serine which is then deaminated to pyruvate. Pyruvate gives rise to acetyl units as acetyl coenzyme A and acetyl phosphate. The latter compound reacts with adenosine diphosphate to yield acetate and adenosine triphosphate, providing the main energy-yielding reaction in the fermentation. The enzyme systems discussed together with their specific activities (mumoles substrate acted upon per hr per mg protein) are as follows: serine aldolase, 9 to 12; serine dehydrase, 180; pyruvate-oxidizing and acyl unit-generating system, 96; phosphotransacetylase, 96; acetokinase, 3,600. The high activity of the acetokinase system may tend to pull the entire reaction series in the direction of acetate and adenosine triphosphate generation. In all cases the reaction rates of the individual enzyme systems were equal to or significantly greater than the over-all glycine fermentation rate by whole cells (9 mumoles per hr per mg protein). If coupled together, these enzymes could account for the fermentation of glycine to acetate, CO(2), and ammonia and could account for the conversion of 2-labeled glycine to doubly-labeled acetate as demonstrated in previous tracer studies.