The Effect of Temperature on the Catalytic Activity of Bovine Carbonic Anhydrase
The two high activity forms of carbonic anhydrase which have been extensively studied, electrophoretic component C of the enzyme from human red cells and electrophoretic component B from bovine red cells, both show remarkably high catalytic activity. Under optimal conditions and at 25 C each molecule of enzyme catalyses the hydration of about 10 molecules of CO2 per second. This observation which is well established, (Kernohan, 1965; Khalifah, 1971) conflicts with a prediction by Eigen and Hammes (1963) that enzymes having acid-base catalytic mechanisms should have an upper limit of about 105 per second to their catalytic rate. This prediction comes directly from the measurement of the rate constants for the combination of protons with various bases in aqueous solution. These rate constants are found to have an upper limit of about 1011M-1sec-1 which corresponds to the collision frequency of the two reactants. For an acid with pK 6 it can be calculated that the rate constant for its dissociation of a proton cannot exceed 105 per second. For acids with higher pK values or whose conjugate bases have lower rate constants for proton addition, the rate constants for proton dissociation will be correspondingly lower. If such a group is successively protonated and then deprotonated during the catalytic action of an enzyme then the rate of the deprotonation reaction will limit the overall catalytic rate which can be achieved.
KeywordsCarbonic Anhydrase Dehydration Reaction Human Carbonic Anhydrase Reaction Trace Bovine Carbonic Anhydrase
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- Dixon, M. and Webb, E.G. (1964). Enzymes. 2nd Ed. London, Longmans.Google Scholar
- Edsall, J.T. and Wyman, J. (1958). Biophysical Chemistry, Vol. 1. New York, Academic Press.Google Scholar
- Eigen, M. and Be Maeyer, L. (1958). Self-dissociation and protonic charge transport in water and ice. Proc.Roy. Soc.(London) 627: 505.Google Scholar
- Eigen, M. and Hammes, G.G. (1963). Elementary steps in enzyme reactions. Adv.Enz. 25: 1.Google Scholar
- Kiese, M. (1941). Kinetic der Kohlensaureanhydrase. Biochem.Z. 307: 400.Google Scholar
- Liljas, A., Kannan, K.K., Bergsten, P.C., Waara, I., Fridborg, K. Strandberg, B., Carlbom, U., Jarup, L., Lovgren, S., and Petef, M. (1972). Crystal structure of human carbonic anhydrase C. Nature New Biology 235: 131.Google Scholar
- Maren, T.H. (1963). Carbonic anhydrase kinetics and inhibition at 37°: an approach to reaction rates in vivo. J.Pharmacol.Exptl.Therap. 139: 129.Google Scholar
- Meldrum, N.Ü. and Roughton, F.J.W. (1933) Carbonic anhydrase. Its preparation and properties. J.Physiol.(London) 80: 113.Google Scholar
- Roughton, F.J.W. and Booth, V.H. (1946). Effect of substrate concentration, pH and other factors upon the activity of carbonic anhydrase. Biochem.J. 40: 319.Google Scholar