142] Flavin peptides

Abstract

The flavin component of succinate dehydrogenases from aerobic cells is covalently linked to the protein, so that even drastic denaturation fails to release the flavin. When succinate dehydrogenase is subjected to extensive proteolytic digestion, the flavin is released in the form of flavin adenine dinucleotide (FAD) peptides of varying chain lengths, depending upon the conditions of proteolysis. The absorption spectrum shows the normal 3-banded spectrum of free flavins but the 375-mμ band is shifted to 345-350 mμ, the exact position depending on the particular peptide. Flavin peptides and their acid-hydrolyzed products show an anomalous pH-fluorescence emission curve. Flavin peptides exhibit a strongly cationic character at the FAD, flavin mononucleotide (FMN), or riboflavin level, so that they may be readily chromatographed on cation exchangers. The procedures for the isolation of the flavin hexapeptide and of the acid-hydrolyzed bound flavin are illustrated. The determination of flavin peptide content in tissues such as heart, where all covalently bound flavin belongs to succinate dehydrogenase, provides an unambiguous means of determining the true succinate dehydrogenase content and the stoichiometry of succinate dehydrogenase to other members of the respiratory chain.