The influence of inorganic nitrogen supply on amination and related reactions in the blue-green alga, Anabaena cylindrica Lemm.
The occurrence of glutamate (GDH), alanine (AlaDH), and aspartate (AspDH) dehydrogenases, glutamine synthetase, ornithine transcarbamylase, and several aminotransferases was demonstrated in preparations of vegetative cells of Anabaena cylindrica cultured on an inorganic medium supplied with gaseous nitrogen or additionally supplemented with either ammonia, nitrite, or nitrate. GDH was mainly NADPH-linked in extracts of algae grown in the presence of atmospheric nitrogen and also ammonia, whilst nitrite and nitrate cultures predominantly showed NADH-linked activity. High activities of both AlaDH and AspDH were recorded in nitrogen-fixing algae; both amino acid dehydrogenases were NADH-specific. GDH in nitrogen-fixing cultures was the only enzyme of reductive amination found in appreciable amount in the lamellar fraction. Glutamine synthetase was most active in alga cultured on nitrogen, whilst greatest ornithine transcarbamylase activity was observed in ammonia-grown filaments. Aspartate-glutamate exceeded aspartate-alanine aminotransferase activity under all culture conditions and both were mainly localised in the supernatant fraction.Changes in activity of the amino acid dehydrogenases were attributed to cofactor competition with reductive processes involved in nitrogen, nitrite, and nitrate assimilation. Glutamine synthetase was considered to be regulated by the availability of ATP, being least under nitrogen-fixing conditions. High ornithine transcarbamylase activity was interpreted to provide a means for removal of excessive levels of ammonia.
Department of Botany, The University, BS8 1UG, Bristol, UK.
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