The GS-GOGAT pathway is not operative in the heterocysts. Cloning and expression of glsF gene from the cyanobacterium Anabaena sp. PCC 7120.
The gene encoding the ferredoxin-dependent glutamate synthase (Fd-GOGAT), glsF, from the heterocyst-forming cyanobacterium Anabaena sp. PCC 7120, has been cloned and sequenced. Unlike other cyanobacteria, Anabaena 7120 contains only Fd-GOGAT, lacking NADH-GOGAT. The amount of glsF transcript and Fd-GOGAT activity were similar under all the nitrogen growth conditions tested. Enzyme activity, Western and Northern blot analyses indicated that Fd-GOGAT is absent in the heterocysts, while glutamine synthetase (GS) and NADP-isocitrate dehydrogenase (IDH) were present in these specialised cells. Our results clearly indicate that the GS-GOGAT pathway is not operative in the heterocysts, and hence glutamate must be imported from the adjacent vegetative cells, to sustain GS activity. Heterocysts probably export glutamine or another nitrogen rich compound like arginine to the vegetative cells.
Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, Centro de Investigaciones Científicas Isla de la Cartuja, Avda Américo Vespucio, s/n, 41092, Sevilla, Spain.
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Martín-Figueroa
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Navarro
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Florencio
D000594:Amino Acid Oxidoreductases / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D017033:Anabaena / Q000201:enzymology* / Q000235:genetics* / Q000254:growth & development; D003001:Cloning, Molecular; D015870:Gene Expression; D005798:Genes, Bacterial; D005970:Glutamate Synthase / Q000235:genetics* / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D012329:RNA, Bacterial / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D012329:RNA, Bacterial; D012333:RNA, Messenger; D000594:Amino Acid Oxidoreductases; D005970:Glutamate Synthase; C042233:glutamate synthase (ferredoxin); D005974:Glutamate-Ammonia Ligase