Isoenzyme pattern of glutamate dehydrogenase as a reflection of nitrogen metabolism in Lupinus albus

Abstract

Glutamate dehydrogenase (L-glutamate: NAD dehydrogenase, EC 1.4. 1.2; GDH) activity and electrophoretic separation pattern of the enzyme were studied. The enzyme was extracted from embryos of Lupinus albus decotyledonized and cultured for 24, 48 and 72 hours in media containing various combinations of saccharose, ammonium chloride, nitrate as well as amino acids: glutamate, aspartate, glutamine and asparagine. The absence of sugar in the medium resulted in an increase of specific activity of GDH, measured by the rate of NADH + H+ oxidation, and induced formation of new isoenzymes of NAD+ - dependent GDH. Most significant increase in GDH specific activity and most evident appearance of new isoenzymes in the embryos were noted when sugar was substituted in the medium by any of the mentioned amino acids. Induction of new isoenzymes could also be seen when ammonium salts were pre-sent in the medium. GHD isoenzymatic patterns were obtained in various trophic conditions. It is suggested that the GDH isoenzyme patterns may serve as a nitrogen metabolism index of a tissue from which the enzyme has been extracted.