Propionate catabolism in the housefly Musca domestica and the termite Zootermopsis nevadensis

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The catabolism of propionate was examined in the housefly Musca domestica (which does not contain detectable amounts of vitamin B 12) and the termite Zootermopsis nevadensis (which contains large amounts of vitamin B 12). The products from carbon-14 labeled propionate were separated by HPLC and radioactivity was determined by liquid scintillation counting. In vivo studies as a function of time showed that, in both species, products of [2- 14C]propionate were acetate and 3-hydroxypropionate. [2- 14C]Propionate was not efficiently converted to methylmalonate or succinate, as would occur in mammals. Studies with sub-cellular fractions in both species showed that only the mitochondrial fraction efficiently converted propionate to acetate. Radioactivity from [1- 14C]propionate incubated with housefly mitochondria was recovered only in fractions corresponding to propionate and 3-hydroxypropionate. The data obtained are consistent with a metabolic pathway in which propionate is converted to 3-hydroxypropionate and then to acetate. The results presented here demonstrate this pathway in insects which have high vitamin B 12 levels and undetectable vitamin B 12 levels, suggesting that this may be a common pathway for propionate metabolism in insects.