p1. The identity of the organism previously known as iVibrio/i O1 (N.C.I.B. 8250) with a species of iMoraxella/i is established. 2. The ability of cells to oxidize propionate is present only in cells with an endogenous respiration and this ability is increased 80-fold when the organism is grown with propionate. 3. Isocitrate lyase activity in extracts from propionate-grown cells is the same as that in extracts from lactate-grown cells, about tenfold greater than that in extracts from succinate-grown cells and slightly greater than half the activity in extracts from acetate-grown cells. 4. With arsenite as an inhibitor conditions were found in which the organism would catalyse the quantitative oxidation of propionate to pyruvate. When propionate was completely utilized pyruvate was metabolized further to 2-oxoglutarate. 5. The oxidation of propionate by cells was incomplete both in a ‘closed system’ with alkali to trap respiratory carbon dioxide and in an ‘open system’ with an atmosphere of oxygen+carbon dioxide (95:5). Acetate accumulated. Under these conditions [2?sup14/supC]- and [3?sup14/supC]-propionate gave rise to [sup14/supC]acetate. The rate of conversion of [2?sup14/supC]propionate into sup14/supCOsub2/sub, although much less than the rate of conversion of [1?sup14/supC]propionate into sup14/supCOsub2/sub, was slightly greater than the rate of conversion of [3?sup14/supC]propionate into sup14/supCOsub2/sub. 6. The oxidation of propionate by cells was complete in an ‘open system’ with an atmosphere of either oxygen or air. Under these conditions very little [1?sup14/supC]propionate was converted into sup14/supC-labelled cell material. The conversion of [2?sup14/supC]- and [3?sup14/supC]-propionate into sup14/supC-labelled cell material occurred at an appreciable rate, the rate for the incorporation of [3?sup14/supC]propionate being slightly more rapid. In the absence of a utilizable nitrogen source part of the [sup14/supC]propionate was incorporated into some reserve material, which was oxidized when added substrate had been completely utilized. 7. [sup14/supC]-Pyruvate produced from [sup14/supC]propionate was chemically degraded. The Csub(1)/sub of propionate was found only in Csub(1)/sub of pyruvate. At least 86% of Csub(2)/sub of pyruvate was derived from Csub(2)/sub of propionate and at least 92% of Csub(3)/sub of pyruvate from Csub(3)/sub of propionate. 8. These results are incompatible with the operation of any of the previously described pathways for propionate metabolism except the direct one, perhaps via an activated acrylate./p
展开▼
