The isocitrate dehydrogenase from cyanobacteria

Abstract

The present communication describes the properties of isocitrate dehydrogenase in crude extracts from the unicellular Anacystis nidulans and from heterocysts and vegetative cells of Nostoc muscorum and Anabaena cylindrica. The activity levels of this enzyme are much higher in heterocysts than in vegetative cells of N. muscorum and A. cylindrica. Isocitrate dehydrogenase is virtually inactive in vegetative cells of A. cylindrica. The enzyme is negatively regulated by the reduction charge and scarcely affected by oxoglutarate in the three cyanobacteria. The inhibition by ATP and ADP is competitive with respect to isocitrate and NADP+ in A. cylindrica and N. muscorum and noncompetitive in A. nidulans. Isocitrate dehydrogenase from the three cyanobacteria seems to be a hysteretic enzyme. All the experimental data suggest that the major physiological role of isocitrate and the isocitrate dehydrogenase in heterocysts is not to generate reducing equivalents for N2-fixation. Oxoglutarate formed by the enzyme reaction is likely required for the biosynthesis of glutamate inside the heterocysts. Thioredoxin preparations from spinach chloroplasts or from A. cylindrica activate isocitrate dehydrogenase from either heterocysts or vegetative cells of A. cylindrica. Activation is completed within seconds and requires dithiothreitol besides thioredoxin. The thioredoxin preparation which activates isocitrate dehydrogenase also activates NADP+-dependent malate dehydrogenase from spinach chloroplasts or heterocysts of A. cylindrica. Isocitrate dehydrogenase from A. cylindrica is deactivated by oxidized glutathione. It is speculated that isocitrate dehydrogenase and thioredoxin play a role in the differentiation of vegetative cells to heterocysts.

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

“…We cannot, however, explain why dithionite did not support proportionally higher acetylene reducing activity follow- (Fig. 1) and then to ␣-ketoglutarate, which would yield reduced ferredoxin and NADPH (5,34). We found no molecular genetic evidence for a second zwf gene in addition to that in the opc operon and have no facile explanation for the low level of G6P-dependent NADPH production in extracts of zwf mutant strain UCD 341.…”

Baltic cyanobacteria – a source of biologically active compounds

“…Usually, when considering cyanobacterial extracts, either specific enzymatic activities were analysed (see, for example: Haystead et al, 1970;Schönherr & Keir, 1972;Papen et al, 1983Papen et al, , 1986Hai et al, 2001;Chiba et al, 2012) or researchers looked for enzyme inhibitors or activators rather than active proteins (Cannell et al, 1987;Lau et al, 1993;Tang et al, 2007;Taori et al, 2008;Zelík et al, 2009;Bláha et al, 2010;Anas et al, 2012;Malloy et al, 2012;Makhlouf Brahmi et al, 2013). It is interesting, however, that similar richness of enzymatic activities and differences in their occurrence were observed within one cyanobacterial genus, when phenotypic and genotypic variabilities among Microcystis strains were studied (Yoshida et al, 2008).…”

Purification and properties of NADP‐isocitrate dehydrogenase from the unicellular cyanobacterium Synechocystis sp. PCC 6803

“…It [6]. In Synechocystis, 2-oxoglutarate inhibited more effectively (Ki = 6 mM), but the intracellular concentrations of this metabolite (25 -200 1M) [25] ruled out a possible physiological effect on IDH activity.…”

“…Apparent K, values were 125, 59 and 12 pM for Mg2+, D,L-isocitrate and NADP, respectively, using Mg2+as divalent cation and 4, 5.7 and 6 pM for Mn2+, D,L-isocitrate and NADP, respectively, using Mn2 + as a cofactor. The enzyme was inhibited non-competitively by ADP (Ki, 6.4 mM) and 2-oxoglutarate, (Ki, 6 mM) with respect to isocitrate and in a competitive manner by NADPH (Ki, 0.6 mM). The circular-dichroism spectrum showed a protein with a secondary structure consisting of about 30% a-helix and 36% P-pleated sheet.…”