title: Hydroxyindole-O-methyltransferase activity in the silkworm (Bombyx mori).
abstract: Hydroxyindole-O-methyltransferase (HIOMT; EC 2.1.1.4) catalyzes the final step in the melatonin (N-acetyl-5-methoxytryptamine) biosynthetic pathway. HIOMT-like activity was detected in the head of fifth last-instar larvae of the silkworm (Bombyx mori), and the optimum pH for this activity was 7.9. The apparent Michaelis constants (K(m)) for S-adenosyl-L-methionine and N-acetylserotonin were 87.6 microM and 96.6 microM, respectively. When the silkworms were entrained to a 12 h light/12 h dark lighting schedule, the HIOMT-like activity showed a significant diurnal variation with high levels during the dark period. The diurnal variation in the activity persisted in constant darkness, but was suppressed by constant light. These findings demonstrate that HIOMT-like activity in the silkworm head occurs as a circadian rhythm and that the rhythm entrains to environmental light/dark cycles. The melatonin rhythm in the silkworm head may therefore be regulated not only by serotonin N-acetyltransferase (EC 2.3.1.87), but also by HIOMT.
authors.affiliation: Department of Chemistry, St. Marianna University School of Medicine, Kawasaki, Japan.
authors.forename: M T
authors.initials: MT
authors.lastname: Itoh
authors.forename: T
authors.initials: T
authors.lastname: Nomura
authors.forename: Y
authors.initials: Y
authors.lastname: Sumi
mesh_terms: D000121:Acetylserotonin O-Methyltransferase / Q000378:metabolism*; D000818:Animals; D012831:Bombyx / Q000378:metabolism*; D001921:Brain / Q000201:enzymology*; D002940:Circadian Rhythm / Q000502:physiology; D003624:Darkness; D007700:Kinetics; D007814:Larva; D008027:Light; D008550:Melatonin / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D011863:Radioimmunoassay; D012436:S-Adenosylmethionine / Q000378:metabolism; D012701:Serotonin / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D009419:Nerve Tissue Proteins; D012701:Serotonin; D012436:S-Adenosylmethionine; D000121:Acetylserotonin O-Methyltransferase; D008550:Melatonin; C006389:N-acetylserotonin