pH-Profile of the Kinetic Parameters of Ribonuclease T1

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Abstract
1. Kinetic parameters, Km and Vmax, of RNase T1 [EC 2.7.7.26] were obtained using G-cyclic-p as substrate at various pH's. From the pKm-, log Vmax-pH profile, two pKa's of free enzyme (pKe) and pKa of enzyme-substrate complex (pKes) were estimated (pKe 5.7 and about 7.5; pKes 3.7, 6.7 and about 7.4). 2. From the pKt-pH. profile of RNase T1 using G-2′-p as competitive inhibitor, the pKe values of 5.7 and about 7.5 were also obtained. 3. Based on the values obtained above, the possibility of the presence of histidine residues in the active site of the enzyme was discussed. 4. From the pKt- and pKm-pH profile, the preferable binding form of G-2′-p with the enzyme was presumed to be monoanionic species.

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