The effect of substrate concentration, pH and other factors upon the activity of carbonic anhydrase

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Abstract
The Michaelis constant was found to be independent of pH its value at 0[degree] = 0.009 [image] CO2 [plus or minus] 0.001. In the pH range in which CO2 uptake and output could both be measured, carbonic anhydrase catalyzed each equally. The effect of pH was studied over the range pH 5.6-10.0 using cacodylate, phosphate, veronal, and dimethylglyoxaline buffers. The inhibitory effect of these buffers was negligible below 0.05 [image]. The pH curve showed a minimum between 6.0 and 7.0, and was still rising at pH 10. The shape was probably not that of the ionization curve of a univalent weak acid, as previously reported. The anions of many neutral salts were found to be inhibitory at pH 7.4 when present in cones, of 0.02-0.1 [image], the series running SO4 < Cl- Br-, NO2-, I-. The enzyme was strongly inhibited in the bicar-bonate-carbonate soln. used in the Philpot method of estimation, and an alternative all-liquid method using veronal buffer was therefore proposed.