Synthesis of the flavocoenzyme of monoamine oxidase.

Previous studies of Igaue, Gomes and Yasunobu [l] and Erwin and Hellerman [2] suggested that the liver and kidney monoamine-oxidase (MAO) coenzyme, an FAD derivative, is covalently linked to the protein. Upon hydrolysis it is degraded in consecutive steps to the mononucleotide and the riboflavin-oligopeptide (“MAO-flavin”) level. ESR and absorption spectra of MAO-flavin [3] indicated that the peptide chain is coupled to the flavin nucleus at position 8a as in the case of flavin in succinate dehydrogenase (“SD flavin”) [4-71. In contrast to SD-flavin (cf. the scheme 1) the fluorescence of MAO-flavin as compared to that of riboflavin is quenched over the whole pH range. Recently the peptide sequence of MAO-flavin was determined and the amino acid linked to the h-carbon was shown to be cysteine in thioether linkage [6]. This structure