The Tricarboxylic Acid Cycle of Heterogeneous and Swarmer Cell Populations of Rhodomicrobium vannielii Rm5

Abstract

Studies on the tricarboxylic acid cycle of Rhodornicrobium vannielii Rm5 demonstrated that, unlike other Rhodospirillaceae, this organism has a functionally incomplete cycle, broken at 2oxoglutarate dehydrogenase, under photoheterotrophic conditions. This enzyme was, however, synthesized when Rm. vannielii was grown under microaerophilic chemoheterotrophic conditions. The citrate synthase exhibited responses to inhibitors characteristic of Gramnegative organisms but, unlike many microbes exhibiting an incomplete cycle, was not inhibited by 2-oxoglutarate. Both NAD-and NADP-linked isocitrate dehydrogenase activity was detectable but the functional roles of these enzymes are unclear. No significant differences in enzyme activities or inhibitor sensitivities of enzymes were detected between heterogeneous cultures and synchronous swarmer cell populations. Ahbreriatiun: TCA, tricarboxylic acid. 0001-2902 0 1986 SGM

Eubacterial isocitrate dehydrogenase with dual specificity for NAD and NADP from Rhodomicrobium vannielii

“…In this report we show that in a purple photosynthetic eubacterium, Rhodomicrobium vannielii [3,14] a dual specificity ICDH is present which shows some kinetic features in common with the archaebacterial enzyme.…”

“…The relatively low affinity of the enzyme for NAD would explain previous observations of much lower NAD-linked ICDH activities in cell-free extracts of Rm, vannielii compared to those of the NADP-linked activity [14], since it is now clear that a sub-optimal NAD concentration was used in these assays. vannielii possesses an ICDH with dual specificity for both NAD and NADP.…”

“…Calculation of the theoretical enzyme activity for one enzyme capable of using both NAD and NADP was performed as described previously [12,14]. The reaction was started with isocitrate and the absorbance increase monitored at 340 nm.…”