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Brain Monoamine Oxidase and Replacement of its Coenzyme Flavin in Rats^1,2,3,

Department of Biochemistry, University of Maryland School of Dentistry, Baltimore, MD 21201

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.

KEY WORDS: • monoamine oxidase • flavin coenzyme • brain mitochondria

¹ Supported in part by Grant No. CA-18691 from the National Cancer Institute.

² This report constitutes part of the thesis submitted by D. A. Dix for the M.S. degree, University of Maryland, 1979.

³ Presented at the 146th National Meeting of AAAS, 3–8 January 1980, San Francisco, CA, abst. 229, p. 128.

⁴ To whom reprint requests should be sent.

Manuscript received 8 December 1980.