157] The enzymatic synthesis of riboflavin

Abstract

Publisher Summary This chapter discusses the enzymatic synthesis of riboflavin. Two-carbon fragments are utilized for the synthesis of the o-xylene portion of riboflavin, and the location of radioactivity from 14C-labeled glucose is traced, especially in the ribityl group. Two substances structurally related to flavins: 6,7-dimethyl-8-ribityllumazine and 6-methyl-7-hydroxy-8-ribityllumazine are isolated from a number of riboflavin-producing organisms and prepared by chemical synthesis. Degradative methods for the localization of isotopes from precursors in various portions of the lumazine and flavin molecule are described. The riboflavin synthetase reaction involves removal of the 4-carbon portion containing carbons 6 and 7 and the adjacent methyl groups from one molecule of 6, 7-dimethyl-8- ribityllumazine and its transfer to a second molecule of the lumazine. The various synthesis method and properties of 6, 7-Dimethyl-8-ribityllumazine are discussed. Riboflavin synthetase activity is measured by a spectrophotometric assay. The methods of column chromatography are used principally for the separation, identification, and quantitative determination of reactants and products of the riboflavin synthetase reaction. Riboflavin synthetase of high specific activity is obtained from Ashbya gossypii and yeast; partially purified enzyme is prepared from E. coli and spinach.