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Pineal Gland Hydroxyindole‐O‐Methyl Transferase (HIOMT) From Rainbow Trout (Salmo gairdneri) Subject to Temperature‐Dependent Substrate Inhibition by N‐Acetylserotonin
Author(s) -
Morton Dougal J.,
Forbes Heather J.
Publication year - 1989
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/j.1600-079x.1989.tb00439.x
Subject(s) - melatonin , incubation , trout , substrate (aquarium) , salmo , medicine , endocrinology , biology , rainbow trout , enzyme assay , michaelis–menten kinetics , enzyme , chemistry , biochemistry , fish <actinopterygii> , ecology , fishery
The effect of different incubation temperatures on the activity of trout hydroxy‐indole‐O‐methyltransferase (HIOMT) was determined in order to study the potential effects of changes in environmental temperature on production of melatonin. In the study, N‐acetylserotonin (NAS) was found to inhibit trout pineal HIOMT, inhibitory concentration decreasing with a decrease in incubation temperature. An increase in incubation temperature was accompanied by an increase in maximal velocity (V m ) and a decrease in affinity of the substrate NAS for the enzyme, while the affinity of the inhibitor NAS remained more or less constant with increase in temperature up to 30°C. It was interesting to note that at subinhibitory concentrations of NAS, possibly concentrations within the normal physiological range, there was a balance between increased velocity and decreased affinity for substrate, with increase in temperature resulting in a constant rate of melatonin production. On the basis of these results it is suggested that substrate inhibition might be involved in modulation of melatonin production and that trout pineal HIOMT can maintain a constant rate of melatonin production over a wide range of temperatures by a combination of compensatory changes in enzyme kinetic parameters.