Steady-state kinetics of glutamate dehydrogenase from Pisum sativum L. mitochondria

Abstract

Glutamate dehydrogenase [ l-glutamate:NAD + oxidoreductase (deaminating) EC 1.4.1.2]has been purified 487-fold from pea stem mitochondria. The enzyme has a specific activity in the presence of 1 m m CaCl 2 of 54 Enzyme Commission (EC) units. Calcium, manganese, and zinc ions activate the reductive amination reaction. The [Ca 2+] 0.5 for activation by calcium is 9 μ m. The extent of activation by calcium changed during purification and storage. The oxidative deamination was slightly inhibited by calcium. The pH optimum for the reductive amination reaction was 8.0 and for the oxidative deamination was 9.2. At pH 8.0 and in the presence of 1 mm CaCl 2 with the ionic strength held constant the enzyme showed normal kinetics for the reductive amination reaction. Under identical conditions except for the absence of CaCl 2 the oxidative deamination reaction showed normal kinetics for glutamate. There was substrate activation at high NAD + concentrations and these concentrations were avoided in the kinetic analysis. A steady-state kinetic analysis showed that a simple mechanism could not be in effect and a partially random mechanism is proposed.