Pathway of formation of branched-chain volatile fatty acids in Ascaris mitochondria.

Disrupted Ascaris mitochondria formed 2-methylbutyrate (2-MB) and 2-methylvalerate (2-MV) when incubated anaerobically with acetyl CoA, propionyl CoA and NADH. However, when mitochondrial membranes were removed by high speed centrifugation and the mitochondrial soluble fraction was incubated with the same substrates, 2-methylcrotonate (tiglate) and a compound tentatively identified as 2-methyl-2- pentenoate accumulated rather than 2-MB or 2-MV. These data suggest that the terminal reduction of the unsaturated intermediates to the saturated 2-MB and 2-MV was catalyzed by an enzyme system at least partially bound to membranes. This supposition was further supported by the findings that disrupted Ascaris mitochondria also formed 2-MB and lesser amounts of 2-MV when incubated with tiglyl CoA plus NADH, and both soluble and membrane-bound components appear to be involved in this reduction. The possibility that electron transport associated ATP synthesis may be coupled to these reductions remains to be examined.