Glutamate synthase in rice root extracts and the relationship among electron donors, nitrogen donors and its activity

The presence of glutamate synthase (GOGAT) in rice root extractsand the relationship among electron donors, nitrogen donorsand its activity were studied using ¹⁵N-amido-labelled glutamine,asparagine, ¹⁴C-2-oxoglutarate and inhibitors The high molecular fraction of rice root extracts prepared bySephadex G-50 column showed ferredoxin-dependent GOGAT activity,but pyridine nucleotide dependent activity could not be detectedin it. Asparagine did not act as a nitrogen donor for rice rootGOGAT. Methyl viologen could be a substitute for ferredoxin,but GOGAT activity with it was about 1/4 of that with ferredoxin.Accordingly, rice root GOGAT was considered to be the same typeas that observed in leaves of many higher plants, but differentfrom that discovered in pea roots and cultured carrot tissues. The extracts showed high GDH activity, which was reduced bythe addition of glutamine. The GDH did not act with glutamineand asparaginc in the presence of aminooxy-acetate and did notshow GOGAT-like activity. (Received December 19, 1977; )