Characterization of preprorelaxin by tryptic digestion and inhibition of its conversion to prorelaxin by amino acid analogs.

We studied the in vitro synthesis of relaxin--an ovarian protein hormone related to the insulin subset of growth factors. RNA isolated from corpora lutea of pregnant sows directed the synthesis of a Mr = 23,000 protein in an ascites tumor cell-free system. This protein contained all of the cysteine-bearing tryptic peptides of relaxin as determined by precise co-migration of tryptic fragments of relaxin precursor generated in vitro and those of highly purified relaxin isolated from sow ovary. Based upon these data, it is likely that the primary translation product of porcine relaxin shares structural homology with preproinsulin. The Mr = 23,000 precursor to relaxin is converted to a Mr = 20,000 prohormone in the presence of ascites microsomal membranes. This conversion and the membrane translocation phenomenon which accompanies it can be inhibited in vitro by the use of beta-hydroxyleucine, an amino acid analog. Use of amino acid analogs may represent a technique to allow study of the conversion of relaxin precursors to relaxin in the luteal cell.