Table 3.

Kinetic parameters characterizing the cleavage of poly(I) as a function of pH for RNase Sa and the 3K and 5K variants a

	pH	kcat(s−1)	KM (mM)	kcat/KM (mM s)−
Wild type	4.02	2.2	0.25	8.8
	4.47	14.2	0.24	59
	5.05	59	0.21	281
	5.60	131	0.18	728
	6.05	175	0.16	1094
	6.50	178	0.15	1187
	7.06	146	0.19	768
	7.50	95	0.26	365
	8.01	42.1	0.29	145
	8.50	5.6	0.34	16
3K	4.00	1.5	0.75	3.3
	4.50	7.5	0.57	13
	5.00	24	0.33	73
	5.50	70	0.26	269
	6.00	98	0.18	544
	6.50	112	0.14	800
	7.06	88	0.14	629
	7.48	51	0.19	268
	8.00	26	0.20	130
	8.48	8	0.24	33
5K	4.47	0.3	1.10	0.3
	5.04	1.2	0.64	1.9
	5.60	4.7	0.47	10
	6.05	7.7	0.23	34
	6.50	11.1	0.13	85
	7.06	10.5	0.10	105
	7.50	6.7	0.10	67
	8.10	3.5	0.11	32
	8.50	1.3	0.14	9.3

^a Measured at 25°C in the presence of 0.05 M Tris, 0.1 M potassium chloride and 0.05 M sodium acetate as described in Materials and Methods.