STRUCTURE AND SIGNIFICANCE OF MANDIBULAR ORGAN-INHIBITING HORMONE IN THE CRAB, CANCER-PAGURUS - INVOLVEMENT IN MULTIHORMONAL REGULATION OF GROWTH AND REPRODUCTION

Current evidence indicates that methyl farnesoate is the crustacean eq uivalent of the juvenile hormones of insects. This putative hormone is produced by the mandibular organs and is negatively regulated by a ne uropeptide produced and secreted by the X-organ-sinus gland complex of the eyestalk. To identify this neuropeptide, a bioassay was developed which measures the inhibition of methyl farnesoate synthesis by mandi bular organs exposed to fractionated sinus gland extracts from the cra b, Cancer pagurus. Two neuropeptides, named mandibular organ-inhibitin g hormones (MOIH-1 and -2) repressed methyl farnesoate synthesis. MOIH -1 was fully sequenced by automated Edman degradation of endoproteinas e-derived fragments and further characterized by mass spectrometry. Th is peptide consisted of 78 residues (M(r) 9235.6), with unblocked term ini and three intrachain disulfide bridges. MOIH-2 appeared to be almo st identical to MOIH-1 with the exception of a Gin for Lys substitutio n at position 33. Comparison with previously sequenced crustacean neur opeptides shows that these MOIHs are members of the ever expanding cru stacean hyperglycemic hormone family, with significant sequence simila rity to molt inhibiting hormones (MIHs). It is possible that these two structurally similar peptides (MIH, MOIH) may control mutually exclus ive physiological phenomena (somatic and gonadal growth), suggesting a complex hormonal integration of these processes in crustaceans.