A Kinetic Study on Ribonuclease T₁ using Dinucleoside Phosphates as Substrates

Abstract

1. Kinetic parameters, K_m and V_max, of RNase T_l [EC 2.7.7.26] were obtained usineg dinucleoside phosphate, GpX (GpA, GpC, GpG and GpU), as substrate at pH 7.5 and 5.0. K_m values of four GpX's were similar order of magnitude, but V_max values of them were decreas-ing in the following order; GpC>GpG>GpA>GpU.
2. From the pK_m-pH profile of RNase T_l at pH from 5.0 to 2.5 using GpC as substrate, pK_e value of 3.5 was obtained.
3. From the pK_i-pH profile of RNase T_l using G-2'-p as competitive inhibitor, the pKe value of 3.4 was also obtained.
4. Based on the values obtained above, the possibility of the presence of a carboxyl residue in the active site of the enzyme was discussed.