Abstract
The correlation between isocitrate lyase and isocitrate dehydrogenase in Proteus vulgaris was investigated under aerobic condition.
Under aerobic and anaerobic conditions, only glyoxylic acid was identified as keto acids in citrate metabolism by sonic extract, and α-ketoglutarate was not detected unless NADP was added.
The sonic extract has an ability to oxidize citrate, isocitrate, succinate, and NADPH. Isocitrate dehydrogenase activity was also confirmed in this extract.
The oxidation of citrate was accelerated by the addition of NADP. The oxidation was inhibited almost completely by malonate and cyanide in the absence of added NADP, however, the inhibition rate was low in the presence of added NADP.
Both NADPH dehydrogenation and oxidation were not influenced by cyanide, while the dehydrogenation was inhibited remarkably by the inhibitors of flavin enzymes, i.e. chlorpromazine and benzoate.
From these results, we conclude as follows: In the sonic extract of P. vulgaris, (a) under the condition without added NADP, isocitrate is metabolized via isocitrate lyase, and the resultant succinate was oxidized by succinate oxidase system, and (b) under the condition with added NADP, isocitrate dehydrogenase is able to operate together with isocitrate lyase, and the NADPH generated is oxidized by flavin enzyme.
