Reaction of ovine prolactin with 2-(2-nitrophenylsulfenyl)-3-methyl-3'-bromoindolemine.

The two tryptophan bonds at positions 91 and 150 in ovine prolactin have been cleaved by the use of 2-(2-nitrophenylsulfenyl)-3-methyl-3'-bromoindolemine. The reaction yielded three products: a small fragment containing residues 92-150, a large fragment consisting of residues 1-91 and 151-199 joined by a disulfide bond, and a derivative containing uncleaved but oxidized prolactin. The yield of the two fragments was 38% and 26%, respectively, indicating a cleavage of approximately 55% for each tryptophan residue. The products were characterized by exclusion chromotography, amino acid analysis, isoelectric focusing on polyacrylamide, circular dichroism spectra, two-dimensional chromatography/electrophoresis on tryptic digests, and ultraviolet absorption spectra. The oxidized but uncleaved product had immunological activity, whereas the two fragments had none. None of these derivatives was active as assayed by the pigeon crop-sac test.