Studies on the synthesis of riboflavin by a mutant yeast, Saccharomyces cerevisiae.

Though the synthesis of riboflavin in large amounts by microorganisms has been encountered, very little is known about the mechani involved in the biosynthesis of this vitamin. A critical examination of the various environmental conditions for different organisms producing this vitamin showed that the optimum conditions for the production of riboflavin varied widely from organism to organism (Schopfer, 1944; Burkholder, 1943; Mayer and Rodbart, 1946). The present investigation with a mutant top yeast strain BY 2 (Saccharomyces revfuiie), obtained from a bottom brewery yeast strain BY 1 (Subramaniam and Ranganathan, 1946), seemed useful to obtain, by comparison, a better knowledge of the mechanism of biosynthesis of riboflavin. Further, this organism differed from those employed in other laboratories in that it had acquired the property of excreting considerable amounts of riboflavin, whereas the parent strain was incapable of excreting any appreciable quantity of this vitamin. Purines, pyrimidines, and amino acids were tested for their effects on the biosynthesis of riboflavin since, with the determination of its nutritional requirements (Premabai, 1947) and certain environmental conditions influencing the elaboration of this vitmin (Mitra, 1950, 1952), it became possible to test these compounds for their activity. Purines and pyrimidines were selected because of their natural occurrence and their marked similarity in chemical structure to riboflavin. A simia attempt has been made recently to interpret the role of these compounds in the biosynthesis of riboflavin by Eremothecium ashbyii (MacLaren, 1952). Since the source of nitrogen is also an important condition for the growth as well as excretion of riboflavin by the microorganism (Burkholder, 1943), experiments were designed, to test the effectiveness of supplemented sources of organic nitrogen, such as asparagine and various amino acids, in addition to the supplied inorganic ammonia. EXPERIMENTAL METHODS