SOLVATION EFFECTS UPON THE THERMODYNAMIC SUBSTRATE ACTIVITY - CORRELATION WITH THE KINETICS OF ENZYME CATALYZED-REACTIONS .1. EFFECTS OF ADDED REAGENTS SUCH AS METHANOL UPON ALPHA-CHYMOTRYPSIN

Solvents, detergents, etc., have often been added to the medium to study the kinetics of enzyme action and for binding studies. They have been employed for diverse reasons such as solubilization of substrates or to stabilize an enzyme that was originally membrane bound. Thermodynamic considerations dictate that any added substance, such as methanol, which is present in significant quantity must affect the thermodynamic activities of the enzyme, enzyme-substrate complex, substrate and any other intermediates although cancellation effects may occur in this regard. The influence upon substrate activities is the only one that is easily experimentally accessible. These effects are shown, from the data of Bernard and Laidler, to be large in the case of the alpha-chymotrypsin catalyzed hydrolysis of methylhydrocinnamate. The variation of the Michaelis-Menten constant is quantitatively explainable in terms of the alteration of the thermodynamic activity of the substrate by methanol.