. Author manuscript; available in PMC: 2009 Nov 18.

Published in final edited form as: Biochemistry. 2008 Oct 23;47(46):12028–12036. doi: 10.1021/bi801473w

Table 4.

Maximal values of rate constants for hydration of CO₂, for hydrolysis of p-nitrophenylacetate, and for proton transfer in the dehydration direction catalyzed by HCA II and variants.^a

Variant of HCAII	Orientation of His64	(k_cat^ex/K_eff^CO²)^b hydration	k_cat/K_m esterase	k_B^b dehyd
		μM^-1s^-1	M^-1s^-1	μs^-1
wild type	in/out	120	2800	0.80
N62T	in/out	69	2880	0.39
N62D	out	53	1900	0.043
N62A	in	81	2220	0.39
N62V	in	83	2360	0.35
N62L^c	in	140	2050	0.20^d

The standard errors for these rate constants are 20% or less.

Measured from the exchange of ¹⁸O between CO₂ and water using eqs 5 and 6.

These data from Fisher et al. (18)

This value estimated from poorly resolved pH dependence shown in Fisher et al. (18)