GROWTH FACTORS 107 



Shigella dysenterice requires (M /xg./ml. of nicotin- 

 amide for growth but higher concentrations have an 

 inhibiting effect. This is probably analagous to the 

 inhibition of enzyme action by an excess of one or more 

 of the products . 



Nicotinamide forms part of the molecule of Harden 

 and Young's cozymase or Co -enzyme I, a di23hosphopy- 

 ridine nucleotide, and of Co -enzyme II, a triphospho- 

 pyridine nucleotide, which are concerned in carbohydi^ate 

 metabolism (see Chapter XII). It seems obvious that 

 nicotinamide is required by some organisms for the 

 synthesis of these co-enzymes. Bacteria like Esch. coli, 

 Eberthella typhosa, and Vibrio comma can synthesise the 

 whole CO -enzyme, whilst Staphylococcus and the dysentery 

 bacilli, for example, cannot synthesise the pyridine 

 moiety. H. influenzce cannot s^aithesise any part of the 

 CO -enzyme which must be supplied intact and cannot be 

 replaced even by adenylic acid (adenine-|-d-ribose-|- phos- 

 phate, see p. 332). Nicotinamide can be replaced by 

 Co-enzjones I or II. 



In America the name niacin has been given to 

 nicotinamide in order to avoid the unfortunate association 

 in the public mind with nicotine. This is important as 

 nicotinamide is of interest in human metabolism, a 

 deficiency of it giving rise to pellagra. 



„ , ^, . .^ ^i5J3\o_(jHOH.CO.XH.CH2.CH<,.rOOH. 



Pantothenic acid. — ^^3/ 



CH2OH 



Williams isolated pantothenic acid from a number of 

 sources such as yeast, rice bran, milk, liver and egg 

 white by extraction with 80 i)er cent, methanol. It was 

 shown to be identical with the chick anti-dermatitis 

 factor of liver and to be an important constituent of 

 bios. It is of very widespread occurrence in bacteria, 

 moulds and many plant and animal tissues, a fact which 



