Characteristics of unbuffered gel-immobilized urease particles. I. Internal pH

Abstract

The overall rate of reaction of a gel‐immobilized urease particle necessarily depends upon the hydrogen ion concentrations within the particle. When the particle is unbuffered, the internal hydrogen ion concentrations are a consequence of the local rates of reaction and the rate of egress of the products of hydrolysis. A simple apparatus has been devised which allows a fairly rapid determination of the hydrogen ion concentration in the center of a particle for any given size, enzyme concentration, substrate concentration, and external pH. The products of urea hydrolysis are self‐buffering in the region of pH 8.83 and for an external pH less than the self‐buffering pH, the pH within the particle is increased because of the reaction. When the external pH is greater than the self‐buffering pH, the converse occurs. The pH at the center of the particle approaches the self‐buffering pH with an increase in particle size and enzyme concentration. The external pH necessarily differs in effect when above or below the self‐buffering pH. An increase in the external substrate concentration has a limited effect, simply rendering the local rates of reaction to be of zero order. The center‐line pH and therefore all internal hydrogen ion concentrations depend upon the parameter and the external pH. Differences between the external and center‐line pH values of the order of units are unexceptional. The implications of the internal pH profiles on the local and overall rates of reaction are explored.