The kinetics of binding human prolactin, but not growth hormone, to the prolactin receptor vary over a physiologic pH range.

A member of the family of hematopoietic cytokines, human prolactin (hPRL) serves a dual role both as an endocrine hormone and as an autocrine/paracrine cytokine or growth factor. During investigation of the solution structural properties of hPRL, we have noted a surprising pH dependence of its structural stability over a range from approximately pH 6.0 to pH 8.