418 IX. IIEMATIN ENZYMES, II 



cussed in Section 4. In the liver, catalase is present in a sufficiently high 

 concentration to act in this manner. 



(h) The catalase present in some facultative anaerobes, ccf., E. coli. Proteus 

 vulgaris. Bacillus subtilis, or Staph ijlococcus, appears to afford no protection 

 against the toxic effects of hydrogen peroxide, if the latter is added to the 

 medium or formed in it by such systems as xanthine oxidase, glucose oxidase 

 or autoxidation of ascorbic acid {28 1 ,506, 17 (iO, 17 91).* 



(c) The high concentration of catalase present in erythrocytes fails to 

 protect hemoglobin against oxidation to hem/globin, if hydrogen peroxide is 

 gradually produced in small concentrations by the action of notatin, the 

 glucose oxidase of Penicillium notatum.'f Bingold (270) and others had as- 

 cribed to the erythrocyte catalase the role of protector of hemoglobin against 

 oxidation by hydrogen peroxide. Finally, Keilin points out that the retrans- 

 formation of hydrogen peroxide into oxygen would be a wasteful process. 



Keilin's hypothesis of the peroxidative function of catalase is of great 

 interest and deserves further close study. At present, however, the matter 

 is far from being clear. So far no biological substrate of major importance 

 has been found to undergo this coupled oxidation. While the conditions for 

 the peroxidative action of catalase may be present in the mammalian liver 

 and erythrocytes, where its concentration is exceptionally high, this does not 

 hold for the majority of cells in which catalase is found. Here its concen- 

 tration is so small that catalatic action, not peroxidative action, is more 

 likely to occur. 



The fact that liver catalase always contains inactive bile pigment hematin 

 catalase (cf. Chapter X, Section 8. '-2,) while erythrocyte catalase is free from 

 it, speaks (in our opinion) strongly in favor of a catalatic function of the 

 enzyme in the mammalian liver. Lemberg and Legge {1705) have shown 

 that the action of hjxlrogen peroxide on catalase in the presence of ascorbic 

 acid oxidizes the enzyme to inactive bile pigment hematin catalase under 

 conditions that would be expected in the liver. The fact that alcohol acts 

 as a philocatalase makes it appear doubtful that the peroxidative action of 

 catalase could lead to a similar autodestruction of catalase. { 



Keilin's theory fails to explain the function of catalase in the erythrocyte. 

 The coupled oxidation of alcohol does not afford protection of hemoglobin 

 against oxidation. If one can conclude from his experiments with notatin 

 that catalase does not protect hemoglobin from oxidation by hydrogen 

 peroxide at all, one must assume that hydrogen peroxide never reaches the 

 red cell. If this is true, the catalase in the erythrocyte is functionless. It 

 will be shown in Chapter XI that there is. nevertheless, good evidence for 

 catalase playing a role in the protection of hemoglobin against oxidation — 



* Herbert and Pinsent {121tJta) found Micrococcus ly.sodeii'ticus to contain about 2% 

 catalase, and doubt whether destruction of hydrogen peroxide can provide a teleological 

 reason for such a high concentration of the enzyme. 



t Catalase protects, however, against hydrogen peroxide formed by D-amino acid 

 oxidase or ascorbic acid {1699). 



t Bonnichsen (i/^o) has recently shown that horse liver catalase contains the same 

 protein as horse erythrocyte catalase. 



