CHAPTER II. 



THE PRODUCTION OF SULPHURETTED HYDROGEN 

 AND ITS ASSIMILATION BY THE SULPHUR BACTERIA. 



Natural Sources of Sulphuretted Hydrogen. 



I. Decomposition of Albuminous Substances. — Animal and 

 plant remains furnish the most important material from which 

 sulphuretted hydrogen is formed. These are attacked by 

 saprophytic microorganisms, and in the resulting decompo- 

 sition sulphuretted hydrogen is liberated. The majority of 

 the forty or fifty natural proteins which occur in plants and 

 animals contain sulphur, and probably about 90 per cent, 

 of the saprophytic organisms in the soil are able to effect 

 the liberation of sulphuretted hydrogen from albuminous 

 material (see p. 26). 



Emil Fischer and his pupils have shown that the protein 

 molecule is built up of amino-acids, so that the liberation of 

 sulphuretted hydrogen will follow from the degradation of 

 amino-acids which contain sulphur. The sole representatives 

 of such acids are cystine, the associated cysteine, and glutathione, 

 which has recently been shown by Nicolet, and Kendall and 

 his co-workers, to be a tripeptide y-glutamyl-cysteinyl-glycine 

 bearing the structure 

 H,N . CH(COOH) . CH, . CH, . CO i NH . CH(CH,SH) . CO ; NH . CH.COOH 



[H^N . CH(COOH)CH, . CH,, . COOH] [H,N . CH(CH,SH)COOH] [H^N . CH^ . COOH] 

 Glutamic acid. Cysteine. Glycine. 



Cystine is COOH . CH(NH2)CHo . S . S . CH^ . CHINH^) . COOH. 

 Cysteine can be converted to cystine by oxidation. 



rCHo— S— H CH2— S— S— CH2 



I II 



2]CH.NH2 +0 >CH.NH2 CH . NH^ + H^O 



I II 



ICOOH COOH COOH 



