THE VITAMIN Ba GROUP VIII. BIOLOGICAL ASSAY OF PYRIDOXAL, PYRIDOXAMINE, AND PYRIDOXINE*

Though various chemical and microbiological methods have been developed for the estimation of vitamin Bs in whole (2-4) or in part (5), animal assays are still necessary for testing the accuracy of these new methods as they apply to animal nutrition. It is also important that the relative potency of pyridoxine, pyridoxamine, and pyridoxal for animals be known. Two different purified rations have been used most frequently for the rat assay. The one devised by Dimick and Schre Aer (6), besides containing the usual purified constituents of a basal ration, also contains beef liver extract, while the one employed by Conger and Elvehjem (7) contains a fullers’ earth filtrate of a butanol extract of 1: 20 liver powder. In either case, the crude extracts contribute a definite but variable amount of vitamin B6 to the basal ration and hence their use constitutes a distinct disadvantage. Further, neither of these two rations allows maximum growth in rats when supplemented with large amounts of vitamin Bs. Clarke and Lechycka (8) have described a biological assay for vitamin Bs in which rats were kept on the deficient diet for a period of 4 weeks or more before feeding supplements containing the vitamin. Since the newer members of the vitamin B complex like biotin, inositol, and synthetic folic acid are now available, the present investigation was initiated with the object of devising a vitamin Bs-free ration which would permit the minimum possible growth of rats on the deficient diet and the maximum growth when optimum amounts of vitamin Be were added.