Hydroxyindole-O-methyltransferase (HIOMT) activity in the pineal of chinook salmon (Oncorhynchus tshawytscha) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6m311r45z

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  • C-methyltransferase (HIOMT) in chinook salmon (Oncorhynchus tshawytscha). Various body tissues, as well as several morphological brain divisions were tested for the presence of HIOMT. Activity was found in the retina, the dorsal portion of the diencephalon, and in the pineal gland of chinook. However, the activity was significantly higher in the pineal gland than in the other tissues. Kinetic properties and the effects of light on enzyme activity were examined for HICMT from the pineal. Optimum reaction conditions were obtained when pineals were homogenized in 0.2 M sodium phosphate buffer, pH 7.6-7.8, incubated at a temperature of between 20° and 30° C, and reaction mixture concentrations of N-acetylserotonin (NAS) and S-adenosylmethionine (SAM) of 5.0 10⁻⁶ and 1.1 X 10⁻⁵ M respectively. Apparent Kr, values were found to be 2.5 X 10⁻⁷ M for NAS and 1.43 X 10⁻⁵ M for SAM. Evidence was found that suggests a positive relationship between fish length and pineal HIOMT activity. This prompted sorting fish into a narrow size range prior to investigating the effects of light on the enzyme. Specific activity of HIOMT was found to exhibit diurnal cycling when fish were maintained in a daily photoperiod of 12 hours of light and 12 hours of darkness. Specific activity continued to cycle in continuous darkness but did not cycle in continuous light or when light was given to the fish during the expected dark-time. It was found that the cycle in specific activity was probably an artifact in this system, since pineal protein content was shown to cycle- diurnally 180° out of phase with the cycle in specific activity while HIOMT activity per pineal did not show any apparent cycling. Preliminary findings indicate that, although no diurnal cycling exists, HIOMT may undergo seasonal variation.
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