THE ROLE OF TRANSCARBOXYLATION IN PROPIONIC ACID FERMENTATION

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Abstract
Experiments were designed to investigate the pathway of propionate formation in cell-free extracts of Propionibacterium shermanii and to determine the fate of the one-carbon unit. The results indicate that the following reactions occur pyruvate is converted to oxalacetate by the transcarboxylation of a 1-carbon unit derived from methylmalonyl Co A and not in equilibrium with free CO2; transcarboxylation is inhibited by avidin, occurring in the absence of CO2 fixation; oxalacetate is reduced to succinate esterified by the transfer of coenzyme A from propionyl CoA; succinyl CoA is converted to methylmalonyl CoA by an isomerization uninhibited by avidin, malonate or charcoal treatment; transcarboxylation of methylmalonyl CoA yields propionyl CoA. A scheme is therefore proposed showing the formation of propionate by interlocked reactions involving a C1 transcarboxylation cycle and a CoA transfer cycle.