TABLE 3.

pK_a values of histidines before and after complex formation

	In subunit		In complex
Residue	Measured	Calculated*	Calculated*
bnH18	7.7†	6.7	6.8
		6.5	6.7
		6.7	6.8
bnH102	5.6‡–6.1§	5.7	3.3
		4.8	−1.0
		5.9	5.9
bsH17	<6¶	5.5	5.7
		1.5	2.2
		6.1	6.4

^*For each histidine, results calculated by three protocols are listed in the order 1), “vdW + ɛ_p = 4,” 2), “SE + ɛ_p = 4,” and 3), “SE + ɛ_p = 20.”

^†Obtained by Loewenthal et al. (1991, 1993) using fluorescence titration.

^‡Obtained by Mossakowska et al. (1989) and Bastyns et al. (1996) from measuring the pH profile of k_cat/K_M for the hydrolysis of GpC.

^§Obtained by Sali et al. (1988) from proton NMR titration in D₂O after correcting for the H/D isotope effect by subtracting 0.2 pKa unit (Loewenthal et al., 1991).

^¶Khurana et al. (1995).