Lipolytic potency of proopiomelanocorticotropin peptides in vitro.

Four lipolytic active centers were localized in proopiomelanocorticotropin (POMC): in the N-terminal part of POMC ("tryptophane rich peptide"), in the N-terminal part of adrenocorticotropic hormone, in the middle portion of beta-lipotropin and in the C-terminal part of beta-lipotropin. The weak lipolytic activity of the "tryptophane rich peptide" is not mediated by its two partial sequences gamma-MSH and delta-MSH. The minimal amino acid sequence for obtaining lipolysis from the N-terminal part of ACTH was ACTH 4-10. Lengthening of this amino acid sequence on the N- or C- terminus resulted in a strong increase of lipolytic potency. The minimal effective sequence from the middle portion of beta-lipotropin was located in the amino acid residues 47-53 which are identical to ACTH 4-10. Additional amino acids on the N- and C-terminus (beta-lipotropin p 41-58 and beta-lipotropin h 35-56) lead also to increased lipolytic activity. The forth center of POMC resides in the C-terminal part of beta-lipotropin (residues 78-91) because sequences from the N-terminal part of beta-lipotropin 61-91 were ineffective. The order of potency of POMC peptides especially in respect to the minimal effective concentration was ACTH 1-13 (alpha-MSH) greater than beta-lipotropin p greater than ACTH greater than ACTH 1-10 greater than beta-lipotropin p 61-91.