Some properties of glutamate dehydrogenase from Agave americana L. leaves

Abstract

Summary The activity of glutamate dehydrogenase from Agave americana L. leaves has been studied. Cell-free extracts and acetone powder extracts from medulla and cortex tissues were used. In any case, the main activity of the aminating reaction was NADH-linked glutamate dehydrogenase. The optimum pH was 8.4. Dialysis increased the enzyme activity. When cell-free extracts of pH 7.0 were incubated at 30°C the specific activity increased sharply to 260–270% within 5 min of incubation. At pH 8.4 a little but significant increase in the specific activity was also observed after 5 min of incubation. The heat stability of the enzyme at 50°C and 70°C has been studied. The purine nucleotides have no effect on the glutamate dehydrogenase from cell-free extracts. Only 5 mM ATP caused a light inhibition of the enzyme activity in dialyzed extracts. 1 mM Zn2+ markedly reduced the glutamate dehydrogenase activity. 50% inhibition was reached in the presence of 10mM Zn2+, both in undialyzed and dialyzed extracts. Ca2+, Mg2+ and Mn2+ at the same concentrations have no effect on the enzyme activity. The glutamate dehydrogenase of cell-free extracts was inactivated by 0.2 mM pyridoxal-5′-phosphate at pH 8.4.