26 BACTEEIAL ENZYMES 



This specificity of enzyme action is important in that it 

 means that an organism such as a bacterial cell must possess 

 enzymes for each process it carries out at a rate greater than 

 that which will occur in the absence of living cells. Consequently 

 an organism which carries out numerous different chemical 

 reactions must contain numerous enzymes in its constitution. 

 If an organism possesses succinic dehydrogenase it will 

 dehydrogenate succinic acid to fumaric acid (or, alternatively, 

 since the reaction is a reversible one, will hydrogenate fumaric 

 to succinic acid in the presence of a hydrogen-donator). If it 

 possesses an enzyme called " fumarase " it will hydrate 

 fumaric acid to L-malic acid; if it possesses L-malic dehydro- 

 genase, malic acid will be dehydrogenated to oxalacetic acid; 

 if it possesses transaminase then oxalacetic acid can be con- 

 verted to aspartic acid, etc. 



CH2.COOH Succinic CH.COOH Fumarase CH2.COOH 



CH2 . COOH dehydrog. CH . COOH CHOH . COOH 



Succinic acid Fumaric acid Malic acid 



Malic CHg.COOH Transaminase CH2.COOH 

 > I > I 



dehydrog. CO. COOH CHNHg.COOH 



Oxalacetic acid Aspartic acid 



So we get a chain of reactions in which each step is catalysed 

 by a specific enzyme. If any one of these enzymes is missing 

 then the chain stops at the substance forming the substrate of 

 the missing enzyme. The distribution of enzymes among 

 bacteria is very varied and, taking this chain of reactions as 

 example, bacteria exist in which four, three, two, one, or none 

 of these enzymes are present and consequently the end product 

 of succinic acid metabolism in various organisms may be 

 succinic acid, fumaric acid, L-malic acid, oxalacetic acid, or 

 L-aspartic acid. Here then lies the key to the variety of 

 chemical reaction displayed by bacteria ; every substance that 

 is metabolised passes through a chain of small alterations, 

 each one involving a simple chemical change and each catalysed 



