Effect of pH on rate of interfacial inactivation of serine proteases in aqueous-organic systems

We studied the inactivation of trypsin and alpha-and beta-chymotrypsin by p assage of droplets of tridecane though their aqueous solutions. The mechani sm involves contact with the interface, because the toss of activity is pro portional to the total area exposed. The rates of inactivation vary up to f ivefold over the pH range 3 to 10. However, there is no clear maximum at th e isoelectric point (pl) of each enzyme, where the amount of protein adsorb ed is usually found to be highest. This is probably because, at the pl, the re is also a minimum in structural alteration on adsorption. There may be a weak correlation with pH effects on foamability of the enzyme solutions, a parameter reported to reflect the "hardness" of different proteins, which controls their interfacial unfolding. The pH dependence of both inactivatio n and hardness cautions against attempts to correlate inactivation of diffe rent enzymes with a single value of a parameter such as adiabatic compressi bility. There is no correlation between the effects of pH on interfacial in activation and those reported in the literature on irreversible inactivatio n in concentrated urea or at high temperature. (C) 2000 John Wiley & Sons, Inc.