STICKLAND KEACTION 165 



cells lose their serine dehydrase activity under conditions 

 similar to those described for loss of aspartase activity and can 

 also be restored by the addition of biotin. This type of 

 deamination is only made possible by the unique structure of 

 the serine molecule. An analogous reaction occurs with 

 cysteine, when the first step is a removal of HgS by " cysteine 

 desulphurase," after which the course of the breakdown is 

 presumably the same as that postulated for serine : 



I 11 - I I 



CHNH2 - H2S > C— NH2 ^=^ C=NH + HoO ^=3^ C=0 + NH3 



COOH COOH COOH COOH 



The cysteine enzyme has also been obtained in a cell-free 

 condition from Esch. coli; it is inactivated by dialysis and 

 the activity restored by the addition of zinc, magnesium, or 

 manganese. 



Deamination by the strict anaerobes 



Some of the Clostridia employ specific methods for the 

 deamination of some amino-acids. CI. sporogenes was first 

 studied by Stickland, who found that washed suspensions of 

 this organism are unable to deaminate any amino-acid if this 

 is added by itself to the suspension. Using reducible dyes 

 as H-donators and acceptors, he found that some amino- 

 acids are deaminated in the presence of a H-acceptor and some 

 in the presence of a H-donator dye; in other words some 

 amino-acids act as H-donators and some as H-acceptors. If 

 two amino-acids, one from each group, are added together to 

 the suspension of organisms, then deamination of both occurs 

 according to the general equation: 



R X R X 



! I L I 



CHNH2 H- H2O -f CHNH2 — > CO + 2NH3 -f CH2 



I II I 



COOH COOH COOH COOH 



In this reaction the molecule R . CHNH2 . COOH undergoes 



