EFFECT OF GROWTH CONDITIONS ON NADPH-SPECIFIC GLUTAMATE DEHYDROGENASE ACTIVITY OF EUGLENA GRACILIS.

Cells of Euglena gracilis Klebs, strain z Pringsheim, had high NADPH-glutamate dehydrogenase (GDH) activity when grown on glutamate but activity was repressed completely in cells grown on ammonium (NH ). Subcellular fractionation showed that NADPH-GDH activity was located exclusively in the cytosol, while glutamine synthetase was present in the cytosol and chloroplasts. Despite high NADPH-GDH activity NH assimilation was completely inhibited by methionine sulphoximine (MSO), an inhibitor of glutamine synthetase. With MSO present, cells produced NH and it was shown that greatest NH production occurred with cells containing high levels of NADPH-GDH activity and plentiful carbon supply. It is concluded that NADPH-GDH has a catabolic function in Euglena generating NH from glutamate under conditions of nitrogen limitation.