The chief objective of this renewal application is the study of the structure-activity relationship of prolactin, LH, FSH and related hormones from various species. We plan to obtain sufficient quantities of the two fibrinolysin fragments, (PRL-(1-53)) and (PRL-(54-199)) of ovine prolactin, and to find optimal conditions to recombne these two fragments for full lactogenic activity. We are also planning to investigate the kinetics of recombination of these two fragments by circular dichroism, as well as the thermal stability of oPRL and its two fibrinolysin fragments. The proposed research also involved modifications of oLH, hLH, and their subunits by specific reagents in order to increase our knowledge of essential groups responsible for biological activity of the native hormones and the recombination of the two subunits. We plan to determine the amino acid sequences of the two subunits of bullfrog and ostrich LH.