A steady-state kinetic study of the ribonuclease A catalyzed hydrolysis of uridine-2′:3′(cyclic)-5′-diphosphate |
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Authors: | Job Ren-Tze Li Frederick G Walz |
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Institution: | Department of Biological Sciences, State University of New York at Albany, Albany, New York 12222 USA |
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Abstract: | Initial velocity measurements were made on the ribonuclease A catalyzed hydrolysis of P-5′-Urd-2′:3′-P in the pH range 4.0–8.0 at 25 °C in 0.1 m Tris-acetate/0.1 m KCl. The pH dependence of the Michaelis constant, Km, the turnover number ks, and for P-5′-Urd-2′:3′-P were similar to those reported for Urd-2′:3′-P (5). When P-5′-Urd-2,3-P and Urd-2′:3′-P were compared under similar conditions the average difference in ks and Km indicated that these parameters were 5-fold and 23-fold lower, respectively, for P-5′-Urd-2′:3′-P. The slight difference in the pH dependence of for these two substrates can be interpreted in terms of a specific interaction of the enzyme at the 5′ position of P-5′-Urd-2′:3′-P, which permits a less exclusive dependence on the ionized state of the free enzyme in binding this substrate. The nature of the interaction of the substrate 5′-phosphomonoester group with the enzyme is discussed in terms of possible interactions with Lys-41 and His-119. |
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