III. PEPTIDES 585 



essential metabolites and meanwhile expand our knowledge in a relatively 

 undeveloped area of comparative biochemistry. 



III. Peptides 



The question of nutritional equivalence of amino acids and intact pro- 

 teins has been raised often since the classical review of the subject by Rose.^" 

 He and his colleagues had shown that, although rats could grow on a puri- 

 fied diet containing known amino acids, much better performance could 

 be elicited with complete proteins. During the decade that followed, im- 

 provements in supplemental rations and in the availability of many of the 

 common amino acids made possible continuing improvements in purified 

 diets. The greater growth that resulted materially reduced the margin of 

 superiority of intact proteins over amino acid mixtures. 



Strepogenin.^^-^^ Against this background, considerable interest was cre- 

 ated by the discovery by Woolley and Sprince" • ^^ of a peptide-like fraction 

 of natural materials that was necessary for growth of a strain of hemolytic 

 streptococci. The material, which was called strepogenin, was also shown 

 to be needed for early growth of L. casei and to promote groAvth in mice.®^ 

 However, its structure has remained unknown, and to the writer's know- 

 ledge no pure samples of strepogenin have been prepared. It is probably a 

 mixture, perhaps of structurally closely related peptides. The best infor- 

 mation has been derived indirectly from degradation studies of insulin,^"- ^' 

 which was thought to have a strepogenin-like pattern in a portion of its 

 structure, together with inhibition studies on lycomarasmin, the tomato- 

 wilting agent of Fiisarium lycopersici SACC. 



Lj^comarasmin acti\nty in tomatoes could be duplicated by tripeptides 

 containing serine, glycine, and aspartic acid.^^ These peptides were also 

 antagonistic to strepogenin for L. casei. Serylglycylglutamic acid was then 

 synthesized and found to possess strepogenin activity, about one-fortieth 

 that of strepogenin concentrates. It was concluded that the latter peptide 

 may be a fragment or a relative of strepogenin. 



6» W. C. Rose, Physiol. Revs. 18, 109 (1938). 

 6> Nutrition Revs. 4, 273 (1946). 

 82 Nutrition Revs. 5. 218 (1947). 

 63 Nutrition Revs. 6, 223, 277 (1948). 

 " D. W. Woolley, Ann. Rev. Biochem. 16, 376 (1947). 

 " E. L. R. Stokstad and T. H. Jukes, Ann. Rev. Biochem. 17, 474 (1949). 

 66 E. E. Snell and L. D. Wright, Ann. Rev. Biochem. 19, 305 (1950). 

 " D. W. Woolley, ./. Exptl. Med. 73, 487 (1941). 

 58 H. Sprince and D. W. Woolley, ./. Exptl. Med. 80, 213 (1944). 

 9 D. W. Woolley, ./. Biol. Chem. 162, .383 (1946). 

 "> D. W. Woolley, ./. Biol. Chem. 171, 443 (1947). 

 " D. W. Woolley, ./. Biol. Chem. 179, 593 (1949). 

 " D. W. Woolley, J. Biol. Chem. 166, 783 (1946). 



