Catalytic Activity of Sub-units of Glutamic Dehydrogenase

Abstract

L-GLUTAMIC dehydrogenase (GDH) has been shown to dissociate into sub-units under a variety of experimental conditions, such as dilution¹, high or low pH^2,3, and presence of DPNH⁴, urea⁵, diethylstilbœstrol⁶, or bicarbonate ions⁷. The relationship between the state of aggregation of the enzyme and its catalytic activity has been the subject of some controversy. Several investigators have attempted to relate the state of aggregation of the enzyme, as studied at high protein concentrations, to catalytic activity measured at protein concentrations several orders lower in magnitude^6,8,9. Recent light scatter studies in this laboratory have shown that if the degree of splitting of the enzyme is plotted against pH and enzyme concentration, a quite irregular mathematical surface results². Consideration of such surfaces plotted from experimental results obtained in the presence of various substrates, coenzymes, and other compounds suggested to us that it is, in general, quite invalid to relate catalytic activity measured under one set of conditions to degree of aggregation of the protein measured under different conditions. We therefore sought to measure both catalytic activity and the degree of aggregation of the protein in identical solutions so that these two properties might be related to each other in a valid manner.