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MULTIPLE BINDING SITES OF HUMAN BRAIN MONOAMINE OXIDASE AS INDICATED BY SUBSTRATE COMPETITION
Author(s) -
White Helen L.,
Wu Joyce Chen
Publication year - 1975
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1975.tb07688.x
Subject(s) - tryptamine , serotonin , phenethylamine , tyramine , monoamine oxidase , biogenic amine , chemistry , monoamine oxidase a , norepinephrine , monoamine neurotransmitter , monoamine oxidase b , dopamine , substrate (aquarium) , biochemistry , enzyme , stereochemistry , biology , endocrinology , receptor , ecology
— Six endogenous substrates of monoamine oxidase (EC 1.4.3.4) (serotonin, l ‐norepinephrine, dopamine, tyramine, tryptamine and β ‐phenethylamine) were used separately and in pairs with human brain mitochondrial extracts. Apparent K 1 values were obtained from experiments in which only 1 of 2 substrates was isotopically labelled, and these values were compared with experimental K m values. β ‐Phenethylamine appears to be metabolized at enzyme active sites independent from those which bind serotonin. The substrate l ‐norepinephrine competes with serotonin for an enzyme site, but also may be catalysed at an additional site which is independent of serotonin binding. Experiments in which [ 14 C]tryptamine was combined with [ 3 E]serotonin indicated that tryptamine is a much more potent inhibitor of serotonin oxidation than was predicted from K m values. It is suggested that the competition among substrates of MA0 which is observed in uitro may have relevance to in uiuo mechanisms for control of biogenic amine concentrations.