Enzymes representative of, and related to, the pentose phosphate pathway, glycolysis, and the tricarboxylic acid cycle have been demonstrated in supernatant and lamellar fractions ofAnabaena cylindricacultured in the presence of atmospheric nitrogen, ammonia, nitrite, and nitrate. Nitrogen-fixing and ammonia-assimilating algae contained essentially similar levels of most enzymes tested, with the notable exception of glyceraldehyde-3-phosphate dehydrogenase which showed increased NADPH-linked activity with concomitant diminution of NADH-linked activity when ammonia was supplied. The provision of nitrite or nitrate caused significant enhancements of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and the related hexokinase and phosphohexoisomerase. Reduced activities of pyruvate kinase, malate dehydrogenase, phosphoenolpyruvate carboxylase, and both NADH and NADPH oxidoreductases were recorded for nitrate-grown alga.
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