32 



SULPHUR BACTERIA 



sulphur bacteria absorb not the HgS, but the hydrosulphide. 

 He is supported in this assumption by the fact that the change 

 from HgS to S is from a lower to a higher level of energy. 

 Interesting figures bearing on this matter have been published 

 by Lewis and Randall : — 



HS~ = S~~ + H+ — 20,470 calories. 

 H2S(aq) - HS- + H+ - 9470 

 H + S(rh) = H2S(aq) + 6490 

 S(rh) + 2O2 = S04~ + 176,500 

 Baas-Becking has utilized these or similar figures to indicate 

 the free energy levels of these compounds in the form of a 

 scale (see Fig. 2). 



It would thus appear that the sulphur 

 199,950^5 bacteria must expend rather than derive energy 



from the conversion of HgS to S. For this 

 reason it is concluded that the necessary energy 

 is obtained by the dehydrogenation of the HS~ 

 according to the following equation : — ■ 

 HS- = H+ + S— . 

 The HS~ is obtained presumably not from 

 HgS but in other ways, as for example by the 

 reduction of oxy-sulphur compounds through 

 the agency of other bacteria. 



Following the scheme of oxidation suggested 

 by Wieland and by Hopkins as taking place in 

 yeast in the absence of oxygen, Baas-Becking 

 suggests that the following represents the 

 reaction by which sulphur develops in the cells 

 of the sulphur bacteria : — 



CH, - S - H 



179,480- -HS" 

 176,500- -S 



170,010- -HzS 



0- 



FlG 



so;- 

 2. 



(i)^ 



CH., - S - S - CH, + 2HS- = 2CH . NH„ + 2SA + 2E 



I " I " I " 



CH . NH2 CH . NH2 C = O 



I I I 



c=o c=o 



R R 



Glutathione 

 (contains cystine and 

 glucosamin) . _ 



E stands for electron 



R 



Compound 



containing 

 cysteine. 



* Refer to p. 20 for the most recent constitution assigned to glutathione. 



