Regulation of isocitrate dehydrogenase from Thiobacillus thiooxidans and Pseudomonas fluorescens

Abstract

The isocitrate dehydrogenases of T. thiooxidans and P. fluorescens have been studied. The apparent K M's for isocitrate are 1.2 × 10 −5 M and 1.5 × 10 −5 M respectively. The apparent K M for NAD + is 2.9 × 10 −4 M for the enzyme from T. thiooxidans while the apparent K M for the NADP-specific enzyme of P. fluorescens is 1.7 × 10 −5 M. ADP and ATP were found to inhibit the isocitrate dehydrogenases of both organisms. Glyoxalate plus oxalacetate caused concerted inhibition of the enzyme from T. thiooxidans. Glyoxalate, when added alone, was an activator of the enzyme from P. fluorescens but increased the inhibition due to oxalacetate and reduced the K I for oxalacetate by three orders of magnitude.