METABOLISM OF PROPIONATE BY SHEEP LIVER. INTERRELATIONS OF PROPIONATE AND GLUTAMATE IN AGED MITOCHONDRIA

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Abstract
Low concentrations of L-glutamate were slowly and quantitatively converted into aspartate by aged sheep-liver mitochondria with the loss of C-1 of the glutamate. When propionate was present in addition the rate of conversion of glutamate into aspartate was increased slightly, and the presence of glutamate caused a marked stimulation in the rate at which propionate was metabolized. The stimulatory effect of "sparker" amounts of L-glutamate on propionate metabolism was matched by the effects of [alpha] -oxoglutarate, pyruvate, citrate and isocitrate, but not by succinate, fumarate, malate or oxaloacetate. Succinate was stimulatory at higher concentrations, whereas oxaloacetate was inhibitory. When propionate was incubated with L-[1-C14]glutamate in the presence of a large excess of un-labelled CO2, some labelling of dicarboxylic acids and aspartate occurred, but this was much less than would have been expected from an obligatory transcarboxylation from C-l of [alpha]-oxoglutarate to pro-pionyl-CoA. Possible mechanisms of these effects are discussed.