Carbon assimilation by Pseudomonas oxalaticus (OX 1). 2. Formate and carbon dioxide utilization by cell-free extracts of the organism grown on formate

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Abstract
Reactions of [C14] formate and [C14] bicarbonate in cell-free extracts (prepared with a Hughes press) of Pseudomonas oxalaticus (OX 1) grown on formate have been studied. The extracts catalyse the incorporation of [C14] bicarbonate into 3-phosphoglycerate in the presence of either ribulose l:5-diphosphate or ribose 5-phosphate plus adenosine triphosphate. These findings show the existence of phosphoribo-isomerase, phosphoribulokinase and carboxydismutase in the extracts. 3-Phospho[C14] glyceric acid is also formed in the extracts from [C 14]formate and ribulose l:5-diphosphate. This enzymic activity is removed by centrifuging the extract and restored by recombining the particulate and supernatant fractions. Incubation under anaerobic conditions reduced the phosphoglycerate formation from [C14]-formate to one-third of that observed on aerobic incubation. Addition of methylene blue restored the anerobic incorporation to 72% of that observed under aerobic conditions. The particulate fraction of the extract oxidizes formate to CO2- These results show that the ribulose l:5-diphosphate-dependent incorporation of [C ]-formate in the extract is preceded by oxidation of the formate to carbon dioxide. The small amount of formate incorporation still observed under anaerobic conditions is considered to be due to experimental limitation and not to some incorporation of formate itself. The extracts incorporate [C14] bicarbonate into malate in the presence of pyruvate and reduced di- or tri-phosphopyridine nucleotide. The latter coenzyme was the more effective. [C14]-Bicarbonate incorporation into malate and oxaloacetate in the presence of phosphopyruvate is catalysed by the extracts.