Different phosphate binding modes of Streptomyces griseus aminopeptidase between crystal and solution states and the status of zinc-bound water

Phosphate shows a non-competitive inhibition toward a Streptomyces aminopep tidase (sAP) between pH 5.85 (K-i = 0.48 mM) and 9.0 (110 mM), with a pK(a) of 7.1 likely due to ionization of H2PO4-. This non-competitive inhibition pattern indicates that phosphate binding to sAP in solution is different f rom that in the crystal structure, where phosphate is bound to the active s ite Zn(II) ions. Fluoride uncompetitively inhibits sAP from pH 5.5 (K-i = 3 .72 mM) to 9.0 (43.6 mM), with a pK(a) of similar to 6.2 likely due to a co ordinated water, The different inhibition natures and pK(a) values indicate that the two inhibitors bind at different locations. (C) 1999 Federation o f European Biochemical Societies.