Effects of α-Ketoglutarate on the Activities of the Glutamate Synthase, Glutamate Dehydrogenase, and Aspartate Transaminase of Sweet Potato, Yam Tuber, and Cream Pea

The regulation of ammonium ion salvage by α-ketoglutarate (αKG) in crops was investigated by photometric assays of the activities of glutamate synthase (GOGAT), glutamate dehydrogenase (GDH), and aspartate transaminase (GOT), isolated from yam and sweet potato tubers (protein-deficient crops) and cream pea (protein-rich crop). Whereas the cream pea GDH and GOGAT were not inhibited by αKG, the yam tuber GDH was competitively inhibited [Ki of 1.3 mM) and the sweet potato GOGAT was noncompetitively inhibited (Ki of 1.0 mM) by αKG. the Km values of GDH and GOGAT for αKG were higher in the yam and sweet potato than in the cream pea. the GOTs were not inhibited by αKG. by inhibiting the GDH of yam tuber and the GOGAT of sweet potato, αKG may be reducing the efficiencies of the crops in ammonium ion salvage and in protein storage. © 1991, American Chemical Society. All rights reserved