Amino acid sequence of the minor isomorph of the crustacean hyperglycemic hormone (CHH-II) of the Mexican crayfish Procambarus bouvieri (Ortmann): presence of a D-amino acid.

The primary structure of the neurohormone crustacean hyperglycemic hormone (CHH-II) was determined by means of enzymatic digestions, manual Edman degradation, and mass spectrometry. CHH-II is a 72 residue peptide (molecular mass 8388 Da), with six cysteines forming three disulfide bridges that connect residues 7-43, 23-39, and 26-52. The peptide has blocked N- and C-termini, and lacks tryptophan, histidine, and methionine. The CHH-I and CHH-II of Procambarus bouvieri have identical sequences and elicit levels of hyperglycemia that are not distinguishable. The difference between the two isomorphs consists in a posttranslational modification of a L-Phe in CHH-I to a D-Phe in CHH-II at the third position from the N-terminus.