Identity of a second type of allatostatin from cockroach brains: an octadecapeptide amide with a tyrosine-rich address sequence.

An octadecapeptide that inhibits juvenile hormone synthesis has been isolated by HPLC from brain-retrocerebral complexes of the cockroach Diploptera punctata. The primary structure of this allatostatin has been elucidated by tandem mass spectrometry: Ala-Tyr-Ser-Tyr-Val-Ser-Glu-Tyr-Lys-Arg-Leu-Pro-Val-Tyr-Asn-Phe-Gly-Leu- NH2 (ASB2). The amidated three-residue C terminus of this type B allatostatin is identical to that of four known type A allatostatins, and the preceding three residues show close structural homology. ASB2 has over twice the activity of the type A tridecapeptide Ala-Pro-Ser-Gly-Ala-Gln-Arg-Leu-Tyr-Gly-Phe-Gly-Leu-NH2 (ASA1) in inhibiting juvenile hormone biosynthesis in corpora allata from females in early vitellogenesis (day 2), and its efficacy persists during pregnancy, but it is equally effective as ASA1 on glands from day-10 females (IC50 = 0.31 nM). The octadecapeptide is characterized by a potential dibasic cleavage site, Lys9-Arg10, the integrity of which is needed for high potency. The ASB2-(11-18)-octapeptide amide gives a full response at high concentrations at day 10 (IC50 = 48 nM), but the C-truncated (1-9)-, (1-11)-, and (1-17)-amide fragments of ASB2 are inactive. Thus, the endocrine message is located at the C terminus. N alpha-acetylation of the N-truncated (9-18), (10-18), and (11-18) fragments of ASB2 increases activity relative to the nonacetylated peptides. The site of action of type A and type B allatostatins is located before mevalonate kinase in the biosynthetic pathway for juvenile hormone.