A. Sreenivasan

Metabolic interrelationships of dietary riboflavin and vitamin B 12 in the rat

In micro-organisms, substance I exhibited some small degree of riboflavin activity for Lactobacillus casei and also had some vitamin B,, potency for Euglena granlis, as well as for some other organisms requiring vitamin B,, (Woolley, 1950, 1951). Addition of substance I to cultures of Bacillus megatherium stimulated vitamin B,, synthesis (Woolley, 1950). The precursor activity of substance I has been further suggested by the observation that an analogue, I ,2-dichloro-4,5-diaminobenzene, competitively inhibited synthesis by B. megatherium of riboflavin and vitamin B,, from substance I (Woolley, 1950). Addition of cobalt, which would normally stimulate synthesis of vitamin B,, by B. megatherium, with this analogue was found to aggravate the inhibition of the synthesis (Woolley, 1950). Addition of substance I, or of the substances that closely resemble it, 5,6-dimethylbenziminazole and o-phenylenediamine, is known to stimulate synthesis of vitamin B,, by Streptomyces olivaceous (Ganguly & Roy, 1956) and by Streptomyces griseus (Dulaney & Williams, 1953). Riboflavin and 5,6dimethylbenziminazole have been shown to cause a small but significant increase in synthesis of vitamin B,, by Escherichia coli (cf. Ford & Hutner, 1955). Added support for the view that biosynthesis of riboflavin and vitamin B,, may involve a common precursor is provided by observations that in media supplemented with cobalt there is an increased synthesis of riboflavin by Ashbya gossypii (Hickey, I 954), and that flavinogenesis by various micro-organisms synthesizing riboflavin was stimulated by additions of certain purines and amino acids (Ford & Hutner, 1955). Since single-carbon fragments may take part in the biosynthesis of riboflavin much in

Effects of Suboptimal and Optimal Intakes of B Vitamins on Protein Utilization by the Growing Rat from Diets Containing Single and Mixed Proteins

B vitamins administered at optimal levels counteract the deterioration in nitrogen re tention and growth rate arising from split feeding of the protein and carbohydrate moieties of the diet. The efficacy of higher dietary levels of B vitamins may be ex pected to differ with the over-all dietary protein quality and has now been ascer tained, employing singleand mixed-protien diets derived from casein, egg albumin and wheat gluten and with variations in levels of thiamine, riboflavin, niacin, pantothenic acid, pyridoxine, folk acid and vita min Bl2.