Table 1.

Rate constants for proton transfer from various sites in human carbonic anhydrase II and site-specific mutants.

Enzyme	donor	distance to Zn a (Å)	kB b (ms−1)	Reference
H64A	4-MI	4.8	Inhibitory	[33]
H64A-T200H	His200	5.2	~300	[34]
H64A-N67H	His67	6.6	200	[35]
wild type	His64	7.5	800	[35]
H64W	4-MI c	8.0	130	[36]
H64A-N62H	His62	8.2	~30	[35]
H64A	4-MI d	12	0	[24]

^aDistance between the zinc and N1 or N3 of the imidazole donor.

^bThe rate constant k_B represents proton transfer to the zinc-bound hydroxide in the dehydration direction of catalysis as described in eq 2 and ref. [24].

^c4-methylimidazole (4-MI) bound at Trp64.

^d4-methylimidazole bound at Trp 5