38 BACTERIAL ENZYMES 



succinic acid, presumably by reason of the similarity of the 

 structures — especially the spatial relations of the two polar 

 groups in the — COOH groups — of substrate and inhibitor. 

 It is characteristic of this type of inhibition that the degree 

 of inhibition depends upon the relative proportions of sub- 

 strate and inhibitor present. It will be seen later that the 

 bacteriostatic action of the sulphonamide drugs has been 

 explained in terms of their competitive inhibition of the 

 essential metabolism of structurally similar ^^-amino-benzoic 

 acid. 



CH2.COOH COOH 



I CH,( 



CH2.COOH ^COOH 



Succinic acid Malonic acid 



H2N /~\ COOH H2N ^"^SOoNHg 



^-Amino-benzoic acid Sulphanilamide 



TYPES OF ENZYMES IN BACTERIA 

 Enzymes are classified according to the reactions which 

 they catalyse. It will have been obvious from the above that 

 an enzyme catalysing a dehydrogenation is called a 

 " dehydrogenase," one catalysing a decarboxylation a 

 " decarboxylase," etc., the name of the substrate usually 

 being specified as well. Bacteria possess a great variety of 

 enzymes and these will be discussed briefly under the general 

 headings set out in Chap. I as indicating the basic reactions 

 carried out by bacteria (pp. 5-6). 



1, 2. Reduction and Oxidation 



Most biological oxidations are of the nature AHg -f B 

 = A + BH2, where the substance AHg is oxidised to A and 

 the substance B reduced to BHg. The oxidation of AHg is 

 catalysed by a dehydrogenase specific for that substrate. 

 Many dehydrogenases have been obtained in a cell-free state 

 from yeasts and animal tissues, but until recently the problem 



