Brain Monoamine Oxidase and Replacement of its Coenzyme Flavin in Rats

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Abstract
The influence of 7-ethyl-8-methylflavin and 7-methyl-8-ethylflavin, vitamin-like homologues of riboflavin, on rat brain mitochondrial monoamine oxidase (MAO) was studied using tyramine as substrate. While riboflavin deficiency caused the enzyme activity to fall to 80% of normal, when 7-ethyl-8-methylflavin replaced riboflavin as the precursor of its coenzyme it caused the activity to fall to 60% of normal. When 7-methyl-8-ethylflavin replaced riboflavin as the precursor of its coenzyme, it caused essentially complete loss of the enzyme activity. We showed that while 7-ethyl-8-methylflavin can serve as a coenzyme for MAO, 7-methyl-8-ethylflavin cannot serve as coenzyme for this enzyme.