Anaplerotic reactions in Anabaena cylindrica

Abstract

Anaplerotic reactions occur in heterocysts and vegetative cells of Anabaena cylindrica. This cyanobacterium possesses phosphoenolpyruvate carboxylase and malic enzyme, but no pyruvate carboxylase and isocitrate lyase. Heterocysts contain all the enzymes for the conversion of glucose 6‐phosphate to oxoglutarate and may not be dependent on a supply with glutamate from vegetative cells.

Properties of the glyceraldehyde-3-P dehydrogenase in heterocysts and vegetative cells of cyanobacteria

“…These investigators could not find evidence for the occurrence of the enzymes of glycolysis and the tricarboxylic acid cycle in heterocysts. Recently, progress has been made in isolating metabolically active heterocysts, and it has become clear that heterocysts possess all the enzymes to convert GAP to oxoglutarate [3][4][5]. Heterocysts contain a thylakoid-bound NADH:plastoquinone oxidoreductase [4,6] which also occurs in the green alga Chlamydomonas [7] and the photosynthetic bacterium Rhodopseudomonas palustris [8] but which is absent in chloroplasts of higher plants.…”

“…The reactions resulting in NADH formation in heterocysts have not yet been investigate d in detail. These cells possess a rather active NAD+-dependent malate dehydrogenase of unknown function [5]. NADH could also be generated by GADPH.…”

Genetic evidence of a major role for glucose-6-phosphate dehydrogenase in nitrogen fixation and dark growth of the cyanobacterium Nostoc sp. strain ATCC 29133

“…The reduction of N 2 to NH 3 by nitrogenase requires the molar equivalent of at least eight electrons and 16 ATP molecules (55). Studies describing enzyme activities and substrates capable of supporting nitrogenase activity in heterocyst extracts implicated either the initial enzymes of the oxidative pentose phosphate (OPP) pathway or those of the Embden-Meyerhof-Parnas, or glycolytic, pathway as the source(s) of reductant required for conversion of N 2 to NH 3 and for respiratory O 2 uptake (1,5,33,53), with vegetative cells supplying the reduced carbon substrate (54). However, there have been neither genetic nor detailed radiotracer experiments to resolve the routes of carbon catabolism in heterocysts.…”

Properties of the glyceraldehyde-3-P dehydrogenase in heterocysts and vegetative cells of cyanobacteria

“…The activities with NADH were 2-6 times higher than those with NADPH, and the rates of this enzyme reaction (Table 1) were comparable or even higher than those with other enzymes of glycolysis and the tricarboxylic acid cycle [5,9]. In all cases, the NAD(P)H oxidations in the extracts were dependent on GAP, ATP, NAD(P)H and therefore due to GAPDH.…”

“…These investigators could not find evidence for the occurrence of the enzymes of glycolysis and the tricarboxylic acid cycle in heterocysts. These cells possess a rather active NAD+-dependent malate dehydrogenase of unknown function [5]. Heterocysts contain a thylakoid-bound NADH:plastoquinone oxidoreductase [4,6] which also occurs in the green alga Chlamydomonas [7] and the photosynthetic bacterium Rhodopseudomonas palustris [8] but which is absent in chloroplasts of higher plants.…”