NUTRITION OF MICRO-ORGANISMS 



more rapid reactions of fi mol. order are almost certainly those in 

 which large numbers of enzymes are involved, and the slower reactions, 

 of mfjL mol. order, those in which only one or a few molecules take part. 

 It is suggested that reactions of the first type are concerned with 

 protein formation, and reactions of the second type with the produc- 

 tion of coenzymes or prosthetic groups. Mcllwain estimates that 

 genes constitute o-i to i % of the protein molecules in a bacterium, 

 which is consistent with the suggested balance between /x mol. and 

 m/x mol. reactions. The significance of the difference between these 

 two types of reaction is that the more rapid reactions are the more 

 likely to be closely related to the unit of inheritance. The precise 

 relation between genes and enzymes provides a fascinating field for 

 future research and one that may lead to an understanding of the 

 fundamental mechanism of heredity. 



Protozoa 



Nicotinic acid or nicotinamide is essential for the growth of Tetra- 

 hymena geleii, and could not be replaced by tryptophan.^* 



References to Section 15 



1. A. S. Schultz, L. Atkin and C. N. Frey, /. Amer. Chem. Soc, 1938, 



60, 1514. 



2. P. R. Burkholder, Amer. J. Bot., 1943, 30, 206 ; P. R. Burkholder 



and D. Meyer, Bull. Torrey Bot. Club, 1943, 70, 372. 



3. A. S. Schultz and L. Atkin, Arch. Biochem., 1947, 14, 369. 



4. M. Rogosa, /. Bact., 1943, 46, 435. 



5. J. M. van Lanen, Arch. Biochem., 1947, 12, loi. 



6. D. Bonner and G. W. Beadle, ibid., 1946, 11, 319. 



6fl. H. K. MitcheU and J. Lein, /. Biol. Chem., 1948, 175, 481 ; J. F. 

 Nye, H. K. Mitchell, E. Leifer and W. H. Langham, ibid., 1949, 

 179, 783. 



7. P. Fildes, Brit. J. Exp. Path., 1938, 29, 239. 



8. M. J. Pelczar and J. R. Porter, Proc. Soc. Exp. Biol. Med., 1940, 



43, 151. 



9. A. Dorfman, S. A. Koser, M. Horwitt, S. Berkman and F. Saunders, 



ibid., 434. 



10. H. F. Fraser, N. H. Topping and W. H. Sebrell, U.S. Publ. Health 



Rep., 1938, 53, 1836. 



11. H. Isbell, J. G. Wooley, R. E. Butler and W. H. Sebrell, /. Biol. 



Chem., 1941, 139, 499. 



12. A. J. Weil and J. Black, Proc. Soc. Exp. Biol. Med., 1944, 55, 24. 



13. S. A. Koser and M. H. Wright, /. Bact., 1943, 46, 239. 



14. L. A. Underkofer, A. C. Bantz and W. H. Peterson, ibid., 1943, 45, 



183. 



15. B. C. J. G. Knight, Bacterial Nutrition ; M.R.C. London, 1936 



16. E. F. MoUer, Angew. Chem., 1940, 58, 204. 



285 



