Physiological adaptations of glutamate dehydrogenase isozyme activities and other nitrogen-assimilating enzymes in the macroalga Bryopsis maxima

• Published in: Plant science (Limerick) 2001-06, Vol.161 (1), p.35-43
• Main Authors: Inokuchi, Ritsuko, Okada, Mitsumasa
• Format: Article
• Language: English
• Subjects: Alga; Biological and medical sciences; Bryopsis maxima; Chlorophyta; Fundamental and applied biological sciences. Psychology; Glutamate dehydrogenase; Metabolism; Methionine sulfoximine; Nitrogen assimilation; Nitrogen metabolism; Phosphorylation; Plant physiology and development
• ISSN: 0168-9452; 1873-2259
• DOI: 10.1016/S0168-9452(01)00386-7

The activities of nitrogen-assimilating enzymes in the marine macroalga, Bryopsis maxima Okamura ex Segawa (Chlorophyta) were studied. Changes in these enzymatic activities were observed during cultivation in a laboratory setting, and after the addition of chemicals. The following results were obtained. (1) The chloroplastic NADP-glutamate dehydrogenase (NADP-GDH; EC 1.4.1.4) increased by 49%, while the cytosolic/mitochondrial NADP-GDH decreased to 23% of its original level, showing organelle-specificity. Chloroplastic and cytosolic glutamine synthetases (GS; EC 6.3.1.2) showed 46% increases in 3 days, followed by decreases to their original levels. Chloroplastic NADPH-glutamate synthase (NADPH-GOGAT; EC 1.4.1.13) showed an increase. Cytosolic NADH-nitrate reductase (NADH-NR; EC 1.6.6.1) decreased to about half its original level in 7 days. (2) A compensatory enhancement of NADP-GDH activity was not observed when the GS activity was completely inhibited by methionine sulfoximine. (3) The chloroplastic NADP-GDH decreased to 82% while cytosolic/mitochondrial NADP-GDH increased to 250% with ATP treatment. These results suggest that the activities of nitrogen-assimilating enzymes are regulated independently in this alga.