... 92 3-1 292, Japan.E-mail: kshiraki@jaist.ac.jpAbbreviations:API,Achromobacter protease I; ASA, accessible surfacearea; Boc, t-butoxycarbonyl; MCA, 4-methylcoumaryl-7-amide;VLK-MCA, Boc-Val-Leu-Lys-MCA.Enzyme: ... surface areas (ASA) of individual residues in the API variants were calculated with the INSIGHT II/DISCOVERsoftware. The radius of the solventprobe was 1.4 A ˚.Measurement of 1H-NMR The pH-dependent1H-NMR ... ASA of the side-chain of His210increased with the decrease in size of the side-chain atresidue 169 (Table 1 and Fig. 3A) . However, the ASAs of Asp113 and His57 remained constant when the side-chain...