Brain monoamine oxidase and replacement of its coenzyme flavin in rats.

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 norma, when 7-ethyl-8-methylflavin 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.