PH-INDUCED TRANSITION AND ZN2-BINDING PROPERTIES OF BOVINE PROLACTIN()

A pH-induced conformational transition was found in bovine prolactin w ithin the physiologically significant pH region from 6.5 to 8.5. The t hermal stability of prolactin at pH 6.5 is essentially higher than at pH 8.5. Bovine prolactin binds zinc ions with an apparent association constant of 2 x 10(5) M(-1) at pH 6.5 and 1x10(4) M(-1) at pH 8.5. The pH dependence of both thermal stability and zinc binding surrounding the pK(a) of histidine suggests that these residues plays a key role i n the structural integrity of bovine prolactin. (C) 1997 Federation of European Biochemical Societies.