588 NEW AND UNIDENTIFIED GROWTH FACTORS 



by the addition of strepogenin-rich proteins. It is possible that lower taste 

 acceptability may have been chiefly responsible for the poorer performance 

 on amino acid mixtures. ^^' ^^ The need for special peptides such as strepo- 

 genin thus seems to be best established for microbial species. Even ^\^th 

 these, the proportion of peptides that is utilized per se is probably very 

 small; in L. casei, strepogenin activity has been claimed for glutamine^^ 

 (although this is not in agreement with the findings of others^^"^^). In 

 spite of the technical difficulties involved, a major demand in this area of 

 investigation continues for purified fractions, so that the nutritional and 

 biochemical roles of these compounds may be further realized, 



IV. Lyxoflavin 



In 1947, Pellares et al.^^ isolated a pentose from human heart, which they 

 identified as lyxose. Later,^''" these workers reported the isolation of lyxo- 

 flavin from the same source, although this was challenged by subsequent 

 work.^**^ 



This close relative of riboflavin (and of the corresponding moiety of 

 vitamin B12) was viewed by Emerson and Folkers^^^- ^^^ as a possible new 

 member of the B complex, although they recognized that the experimental 

 evidence for the reported existence of lyxoflavin was not as rigorous as might 

 be desired. They therefore devised a ration based on soybean meal as the 

 major constituent, to which had been added 0.5 % desiccated thyroid, and 

 observed the rate of growth of rats on this diet. The growth-depressing 

 effect of large doses of thyroid was overcome by extracts of liver and by 

 fish meal, or alternatively by synthetic lyxoflavin. The lyxoflavin efi'ect 

 was shown not to be due to conversion to riboflavin. The ability of lyxoflavin 

 to completely replace the effect of liver or fish meal gave support for its 

 classification as a vitamin for the rat, and its general importance was fur- 

 ther suggested by the findings that it also stimulated s\vine and chick 

 growth. ^"^^ ^°^ It seemed possible from this work that lyxoflavin might be 



3* L. P. Snipper, Ph.D. Thesis, Oregon State College, 1951. 



95 H. T. Peeler, L. J. Daniel, L. C. Norris, and G. F. Heuser, J. Biol. Chem. 177, 905 

 (1949). 



96 L. D. Wright and H. R. Skeggs, J. Bacteriol. 48, 117 (1944). 

 " E. Kodicek and S. P. Mistry, Biochem. J. 51, 108 (1951). 



98 E. Kodicek and S. P. Mistry, Biochim. et Biophys. Acta (In Press). 



99 E. S. Pellares, F. V. Orozco, and J. R. Carvallo, Arch. inst. cardial. Mex. 17, 

 575 (1947). 



1"" E. S. Pellares and H. M. Garza, Arch. Biochem. 22, 63 (1949). 

 1"! T. S. Gardner, E. Wenis, and J. Lee, Arch. Biochem. and Biophys. 34, 98 (1951). 

 102 G. A. Emerson and K. Folkcrs,*/. Am. Chem.. Soc. 73, 2398 (1951). 

 i«3 G. A. Emerson and K. Folkers, ./. /Im. Chem. Soc. 73, 5383 (1951). 

 10" R. C. Wahlstrom and 15. C. Johnson, ./. Animal Sci. 10, 1065 (1951). 

 lo^ H. W. Bruins, M. L. Sundc, W. W. Cravens, and E. E. Snell, Proc. Soc. Exptl. 

 Biol. Med. 78, 535 (1951). 



i 



