Chemical and biological characterization of salmon melanocyte-stimulating hormones

Ten peptides related to melanocyto-stimulating hormone (MSH) have been identified in an acid acetone extract of the chum salmon pituitary. All these peptides are related to the alpha-MSH and beta-MSH families, but no peptide related to gamma-MSH has been found. This result is in accordance with the finding that the gamma-MSH segment is deleted from the N-terminal peptide of salmon pro-opiocortin (NPP I). Based on the structures of newly isolated peptides, the maturation process of MSH is discussed. The major components of salmon MSH were tested for biological activities. In the lipolytic assay with rabbit fat cells, alpha-MSH I and alpha-MSH II were equipotent, but beta-MSH I and NPP I exhibited very low or no activity. On the other hand, the des-acetyl-alpha-MSH I was found to be four times as potent as alpha-MSH I in this assay. The steroidogenic activities of alpha-MSH I and N-des-acetyl-alpha-MSH I were approximately 0.05% of the potency of ovine ACTH. All other peptides exhibited less than 0.01% potency. Salmon alpha-MSHs were found to be somewhat more potent melanophore-stimulating agents than the beta-MSHs.