22 NITROGEN METABOLISM 



CH=CH.CH:CHCOOH (CH2)2COOH 



II I 1 



N NH — >CH(NH2) +HCOOH+NH3 



\ / I 



CH COOH 



(11) 

 Urocanic acid and glutamic acid are also intermediates in 

 the oxidation of histidine by Ps. fluorescens, and isotopes 

 have been used to show that the amino-nitrogen of glutamic 

 acid and the carbon of HCOOH are derived from the N and 

 C in positions i and 2 of the imidazole ring [59]. The fer- 

 mentations of C/. tetani [48Z>]and CI. cochlearum [3] resemble 

 those of CI. tetanomorphum. The former ferments a number 

 of amino-acids, only one of which, histidine, is among those 

 essential for growth; aspartic acid and serine give rise to 

 alcohols as well as to fatty acids. It is well known that yeasts 

 fermenting carbohydrates in the presence of amino-acids 

 produce a number of the higher aliphatic alcohols (fusel oil), 

 and Ehrlich showed that the latter contain one less carbon 

 atom than the amino-acids from which they were derived, 

 the overall reaction being: 



Such a process may be the means whereby the nitrogen of 

 the amino-acid is made available in the form of NH3 , but 

 the details of the mechanism are unknown. Most of the 

 alcohols are formed after the amino-acids have disappeared 

 from the medium, indicating that there are intermedi- 

 ate stages between deamination and production of the 

 alcohol [13]. 



Anaerobic ac- deaminases 



A characteristic feature of the anaerobic a- deaminases is 

 that the reaction product is unsaturated and therefore such 

 enzymes are sometimes described as desaturases. One 

 typical example has already been mentioned, namely, the 

 enzyme forming urocanic acid from histidine, and there is 

 evidence that it also occurs in certain strains of Esch. colt, 

 Salmonella paratyphi and Shigella paradysenteriae [50]. A 

 similar type of reaction is catalysed by aspartase, an enzyme 



