106 BACTERIOLOGICAL CHEMISTRY 



CH3 



/-Leucine.— ^CH.CHa.cH.NH^.cooH, This 



(•H3 



amino -acid is required by yeast for growth in synthetic 

 media and is a constituent of bios. It is classed as one 

 of the essential amino -acids for the growth of most 



bacteria. 



CH 



CH C.CONHo 



Nicotinamide. — 1^ II . Knight found that 



CH CH 



%/ 



]sr 

 nicotinamide was one of the constituents of meat or 

 yeast extract required for the aerobic growth of Staph, 

 aureus on gelatin hydrolysate with the addition of 

 tryptophane, cystine and glucose. It was active at a 

 dilution of 0-05 /xg./ml. of medium. Nicotinic acid, 



CH 



CH CCOOH "^^^ found to be someM^hat less active than the 

 I II ' amide. That the activity is not due to an im- 



^ p^ purity is shown by the fact pyridine-3-nitrile, 



N 

 CH 



CH C.CN, i^ inactive until it is hydrolysed to the acid. 



I II Nicotinamide is also required by Shiga's 



^•^/'^ dysentery bacillus and by Hceinophilus 



pertussis. The ratio of the activity of the amide to that 

 of the acid is not constant but differs for various organ- 

 isms. Thus for C. diphtherice the acid is ten times as 

 active as the amide, for Proteus vulgaris the two are 

 equally active, for Staph, aureus tlic amide is five times 

 as active as the acid, for Shigella dysenterice the ratio is 

 ten to one, whilst some Pasteur ella strains cannot use the 

 acid at all. 



