Studies in Plant Carbonic Anhydrase. II. Kinetic Studies

Abstract

A water extract of leaves of tulip and lamb''s-quarters was shown to catalyze both the dehydration of carbonic acid and the hydration of CO2 in direct proportion to the wt. of the leaf prepn. present in the system. The catalytic rate of carbonic acid dehydration was demonstrated to be pH dependent. In phosphate buffer the opt. pH for activity was 6.5 whereas in veronal buffer the opt. was pH 7.1. Temp, also affected the rate of dehydration of carbonic acid in the presence of the leaf extract. The re action rate increased up to 40C and then decreased abruptly until at 50[degree] no catalytic activity could be demonstrated. The reaction rate also increased as the substrate concn. was in creased up to 4 x 10-2 [image] under the conditions employed and a further increase in substrate gave no greater reaction rate. The kinetic data, which were typical of enzyme-catalyzed reactions, indicated that an enzyme, plant carbonic anhydrase, existed.