A direct pathway for the conversion of propionate into pyruvate in Moraxella lwoffi

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Abstract
The identity of the organism previously known as Vibrio O 1 (N.C.I.B. 8250) with a species of Moraxella is established. 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. Isocitrate lyase activity in extracts from propionate-grown cells is the same as in extracts from lactate-grown cells, about 10-fold greater than in extracts from succinate-grown cells and slightly greater than half the activity in extracts from acetate-grown cells. With arsenite as an inhibitor conditions were found in which the organism would catalyze the quantitative oxidation of propionate to pyruvate. When propionate was completely utilized, pyruvate was metabolized further to 2-oxoglutarate. The oxidation of propionate by cells was incomplete both in a ''closed system'' with alkali to trap respiratory CO2 and in an ''open system'' with an atmosphere of O + CO2 (95:5). Acetate accumulated. Under these conditions, [2-14c]- and [3-14C]-propionate gave rise to [14c]acetate. The rate of conversion of [2-14C]propionate into 14CO2 although much less than that of [1-14C]propionate into 14CO2, was slightly greater than that of [3-14C]propionate into 14CO2. The oxidation of propionate by cells was complete in pn ''open system'' with an atmosphere of either O2 or air. Very little [l-14c]propionate was converted into 14c-labelled cell material. The conversion of [2-14C]-and [3-14C]-propionate into 14C-labelled cell material occurred at an appreciable rate, the rate for the incorporation of [3-14C]propionate being slightly more rapid. In the absence of a utilizable N, source, part of the [14c]propionate was incorporated into some reserve material, which was oxidized when added substrate was completely utilized. [14C]-Pyruvate produced from [14C]propionate was chemically degraded. The C(1) of propionate was found only in C(1) of pyruvate. At least 86% of C(2) of pyruvate was derived from C(2) of propionate and at least 92% of C(3) of pyruvate from C(3) of propionate. These results are incompatible with the operation of any of the previously described pathways for propionate metabolism except the direct 1, perhaps via an activated acrylate.