ANTIBIOTICS 16!) 



powder, soluble in water but not in organic solvents. 

 It is decomposed by 70 per cent, aqueous methanol at 

 30°C. or by aqueous solutions of trichloracetic acid to 

 give a protein and a prosthetic group, neither of which 

 is active alone. Its activity is lost below pH 2 and above 

 j^H 8 or by heating at 60°C. It is not destroyed by 

 pepsin at pR 3-8, trypsin at ^^H 5- 7, takadiastase or emul- 

 sin. It is almost completely inactived by activated papain 

 at pH 3-8. Blocking of the amino groups by formalde- 

 hyde, nitrous acid, or phenyl-isocyanate does not cause 

 loss of activity. It has the properties of a " yellow 

 enzyme," that is a flavoprotein enzyme (see j). 42). 

 In the presence of glucose and oxygen it has a very 

 powerful bactericidal effect on all bacteria which are 

 sensitive to hydrogen peroxide, e.g.. Staph, aureus, 

 Str. pyogenes, Dipl. pyieumonice, E. typhosa, Sal. paratyphi, 

 Sal. schottmillleri, Sal. typhi-murium, V. comma, B. 

 anthracis and Proteus vulgaris. The effect is reversed 

 by the presence of catalase. Xotatin is a glucose 

 aerodehydrogenase which, under aerobic conditions, 

 oxidises glucose to gluconic acid with production of 

 hydrogen peroxide which is the directly lethal agent. 

 Glucose can be replaced by galactose or xylose but not 

 by other sugars. 



The xanthine -oxidase in milk is also a flavoprotein 

 enzyme which catalyses the oxidation of xanthine or 

 hypoxanthine to uric acid and hydrogen peroxide. In 

 the presence of its substrate (present in ordinary meat- 

 broth media but not in peptone water or hydrolysates of 

 purified proteins) the gro^^-tli of organisms sensitive to 

 hydrogen peroxide is inhibited. The effect is eliminated 

 by the presence of catalase, which destroys the hydrogen 

 peroxide formed, or by the absence of the appropriate 

 substrate. The gro\^i;h of E. coli, Bad. lactis aerogenes, 

 Shigella flexneri or C. diphtherice, which are insensitive 

 to hydrogen peroxide, is not affected by either of these 

 enzymes. 



