136 BACTERIOLOGICAL CHEMISTRY 



enzymes. The effect of mercuric chloride as an anti- 

 septic has been regarded for a considerable time as 

 being due to the combination of the mercury with the 

 -SH groups of proteins. Its inhibition of some enzymes 

 such as papain or invertase is held to be due to a similar 

 reaction. 



In 1923 Voegtlin suggested that the phenyl -arsenoxides 

 were lethal to trypanosomes and spirochsetes because 

 they reacted with the sulphydryl groups of glutathone : — 



SG 

 SHG / 



R.AsO + > R.As + HaO, 



SHG \ 



SG 



and so interfered with the respiratory mechanism of the 

 organisms. The addition, in sufficient amount, of com- 

 pounds containing SH groups was capable of reversing 

 the inhibition of enzymes or respiration by the arsenoxides 

 or mercury by themselves combining with the inhibitors. 

 Accordingly when it was discovered that sulphanila- 

 mide was effective against micro-organisms in vitro only 

 when small inocula were used or when the medium did 

 not contain peptone, the suggestion was soon forth- 

 coming that some substance or substances contained in 

 peptone or large inocula were inhibiting the action of 

 the drug. Confirmation of this view was afforded by 

 Stamp in 1939 who showed that addition of killed 

 streptococci to a medium containing sulphanilamide 

 permitted even small inocula of living organisms to 

 survive and flourish. He succeeded in extracting the 

 inhibitor from streptococci with dilute ammonia solution 

 and obtained it as an alcohol soluble substance stable to 

 acid and heat ; it contained an amino group. He 

 regarded it as possibly a complex amino acid required 

 for growth or as an essential part of an enzyme system. 

 Similar results liave been reported for Brucella abortus 

 and other bacteria. 



