Metabolic regulation in Pseudomonas oxalaticus OX1

Metabolic control associated with diauxic growth of Pseudomonas oxalaticus in batch cultures on mixtures of formate and oxalate was investigated by measuring intracellular enzyme and coenzyme concentrations and Q_O2values during transition experiments from oxalate to formate and vice versa. In transition from oxalate to formate oxalyl-CoA reductase concentration declined after the exhaustion of oxalate and ribulose-1,5-diphosphate carboxylase and ¹⁴CO₂ fixation appeared upon addition of formate. In the reciprocal transition, ribulose-1,5-diphosphate carboxylase and ¹⁴CO₂ fixation rate declined sharply after formate exhaustion, and oxalyl-CoA reductase appeared only after addition of oxalate. The intracellular NAD and NADP concentrations measured in the same experiments are reported. At substrate exhaustion the proportion of NAD in the reduced form fell from 15–20% to 2%. On addition of formate to an oxalate-starved culture there was an immediate increase in the proportion of NADH to 50%; such an increase was not observed in the reverse experiment.Abbreviations RuDP ribulose-1,5-diphosphate - HEPES 2-(N-2 hydroxyethylpiperazin-N-yl) ethane sulphonic acid