Amino terminal residue heterogeneity of bovine and ovine growth hormones as revealed by polyacrylamide gel electrophoresis.

Prolonged electrophoresis (4 to 16 h) of bovine and ovine growth hormones on analytical polyacrylamide gels in Tris-EDTA-borate buffers of pH 7.6 to 8.1 resulted in the separation of alanyl, phenylalanyl, and methionyl terminal polypeptide chains of these hormones similar to that obtained by isoelectric focusing in Ampholine pH gradients. Their relative anodic mobilities were methionyl greater than phenylalanyl greater than alanyl. The mobilities of the respective monomers were inversely related to their isoionic points as determined by isoelectric focusing in Ampholine pH gradients. The resolution of the different monomers is attributed to differences in the dissociation constants of the amino groups of the alanyl, phenylalanyl and methionyl terminal residues. Rat growth hormone, which consists of monomers with only a phenylalanyl amino terminus, did not display heterogeneity on gel electrophoresis. The applicability of employing polyacrylamide gel electrophoresis for the assessing of amino terminal residue heterogeneity is noted.