148 RESPIRATION 



Further, this view is supported by the fact that hydrocyanic 

 acid retards the activity of glutathione as it does other oxi- 

 dations supposed to be dependent upon iron. 



The exact function of glutathione in the respiratory mechan- 

 ism is still largely a matter of speculation ; it has been sug- 

 gested that it acts only as a carrier in transferring hydrogen 

 from the substance to be oxidised to the activating iron sur- 

 faces where the hydrogen is to be oxidized, the iron being 

 supposed to be localized upon surfaces and thus to be incapable 

 of moving towards the oxidizable materials, a function which 

 is broadly comparable with that assigned to the respiratory 

 pigments. 



Glutathione is not uncommon in plant tissues although 

 the coloration by which it is recognized usually is far less 

 intense in vegetable than in animal tissue. Its presence in 

 yeast may be demonstrated by grinding the cells in a mortar 

 with a little sand and some saturated solution of ammonium 

 sulphate. On pouring off and adding to the supernatant 

 liquid a few drops of 5 per cent, solution of sodium nitro- 

 prusside and a little strong ammonia, a pink colour is produced. 

 This colour reaction, which also is given by a number of other 

 reducing substances such as aldehydes, acetone, hydrogen 

 sulphide, etc., is only given by the reduced or cysteine form 

 of the dipeptide and not by the cystine or oxidized modification. 



OXIDASES. 



Oxidases * are of wide occurrence in the vegetable kingdom, 

 as should be the case if they are primarily concerned in aerobic 

 respiration, but whether they are present in all living cells 

 is doubtful. According to Atkins f they are absent or inactive 

 in tissues markedly acid in reaction or containing large amounts 

 of reducing substances. Bunzel J also has shown that the 

 activity of these enzymes is inhibited by acids, their greatest 

 activity being at or near the point of neutrality ; the limits 

 of the pH value corresponding to complete inhibition in the 



* See Vol. I., p. 498. 



•f Atkins : " Proc. Roy. Dublin Soc," 1913, 14, 144. 



X Bunzel : " Journ. Biol. Cheni.," 1916, 28, 153. 



