Kinetic Studies of Human Carbonic Anhvdrases B and C*
نویسندگان
چکیده
Carbonic anhydrase preparations from human erythrocytes contain at least three distinct molecular forms of the enzyme (l-4), two of which-denoted here as carbonic anhydrases B and C-have been studied in detail. They differ widely in specific activity, and also in their isoelectric points (1, 4), their amino acid composition (4-6), and their chromatographic behavior (3,4). Earlier studies on the kinetics of human carbonic anhydrase (7-9) were made on preparations that presumably were mixtures of these isoenzymes. DeVoe and Kistiakowsky (9) found that the kinetics of their preparation did not fit the Michaelis-Menten equation. It seemed of interest, therefore, to study the kinetic behavior of the two major forms of the enzyme, now available in quite pure form, and to compare these results with those obtained on earlier preparations of the human and the bovine enzymes. The studies reported here are particularly concerned with the effect of pH on the kinetic parameters of carbonic anhydrases B and C. We have already given a preliminary report of these findings (10). Carbonic anhydrase (EC 4.2.1.1) catalyzes the reaction which we may write adequately for present purposes as
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The carbon dioxide hydration activity of carbonic anhydrase. I. Stop-flow kinetic studies on the native human isoenzymes B and C.
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