56 



INTERMEDIARY METABOLISM AND GROWTH 



rium (Rose, 1949), namely isoleucine, leucine, lysine, methionine, phenylalanine 

 threonine, tryptophane, and valine. Histidine is also required for nitrogen equilib- 

 rium in the adult dog. Although arginine is not needed for nitrogen equilibrium 

 in man, spermatogenesis is reduced in diets lacking in arginine. Sperm cells are 

 rich in arginine. 



The biosynthetic potentiality of the entire animal should be distinguished from that of 

 the individual tissues. The nutritional requirements of two strains of mammalian cells 

 have been studied by tissue culture techniques (Eagle et al., 1956a). Mouse fibroblast cells 

 (Strain L) and human uterine carcinoma cells (HeLa) require 13 L-amino acids for 

 growth. These are arginine, cysteine, histidine, tyrosine, glutamine and the eight amino 

 acids required by the adult for nitrogen equilibrium. In the presence of ammonium ions, 

 glutamic acid can replace glutamine in HeLa but not in mouse fibroblast cells. However, 

 10-20 times as much glutamic acid as glutamine is required. Probably, few mammalian 

 tissues other than liver eflfect a net synthesis of arginine, cysteine, and tyrosine. 



The biosynthetic activities of normal and malignant mouse tissues have been studied 

 with I'^C-labelled substrates. With labelled glucose or acetate (Kit and Graham, 1956b; 

 Busch et al., 1956) radioactivity is incorporated into free alanine, glycine, serine, glutainate, 

 aspartate and proline. The glutamine of diaphragm, liver and brain; and the y-amino 

 butyric acid of brain tissue were also labelled (Kit and Graham, 1956a). In liver tissue, 

 the conversion of labelled acetate to arginine also takes place (Greenberg and Winnick, 

 1949). These results complement those obtained in nutritional studies. 



4. The synthesis of the carbon skeletons of a??iino acids 



(fl) Histidine 



The terminal steps in the biosynthesis of histidine are shown in Fig. 19. The 

 following evidence may be cited in support of this scheme : 



CH — NH 

 II \ 



C84 



•H,0 



C N 



CHOH 



I 

 CHOH 



CHjOPOjHj 



D - Erythro - 

 imidazole glycerol 

 phosphate 



CH— NH 

 II \ 



C N 



I 

 CH2 



c=o 



CH,OPO,H, 



CH — NH 

 II \ 



CH 



C141 



Imidozole 



acetol phosphate 



C-N^ 

 I 

 CH2 



HC— NH, 



I 



CHjOPOjHj 



Histidinol 

 phosphate 



T1710 



CH— NH 

 C — N^ 



6CH2 



7CHNH2 



eCHzOH 

 Histidinol 



DPN'' 



CH — NH 

 II \ 



C- 

 I 

 CH, 



,^ 



CH 



CH — NH 

 II \ 



DPN' 



CHNH2 



COOH 



Histidine 



C — N 



I 

 CH2 



CHNH 

 I 

 CHO 



^ 



CH 



Fig. 19. Histidine biosynthesis. 



/) Imidazoleglycerol phosphate, imidazoleacetol phosphate, and histidinal phosphate 

 accumulate in the culture medium of Neiirospora mutants. Likewise, histidinol has been 



