56 BACTERIAL ENZYMES 



'' energy-ricli," is the source of this utiUsable energy (see 

 Chap. VII). Considerable evidence is now accumulating that 

 the energy obtained from oxidation processes also arises from 

 the formation and breaking of energy-rich phosphate bonds; 

 thus the oxidation of pyruvic acid by pyruvic oxidase of 

 Lactobacillus delbreuckii is accomplished only in the presence of 

 phosphate and involves the formation of acetyl phosphate as 

 the first stage in the reaction : 



CH3 . CO . COOH + H3PO4 + = 



CH3.COOPO3H2 + CO2 + H2O. 



Phosphorylation may occur in many reactions other than 

 those involved in fermentation and oxidation. Examples of 

 phosphorylated intermediates are still being discovered in 

 many metabolic changes as the biochemistry of living tissues 

 is further probed. 



General 



The metabolism of a cell consists of many chemical changes 

 catalysed by various enzyme systems. The biochemist has 

 concerned himself with the isolation of these enzyme systems 

 in an endeavour to identify the steps by which the changes 

 occur and to interpret the mechanism of these changes in 

 terms of the chemistry of the enzyme molecules. The 

 systems outlined in this chapter summarise the types of 

 enzymes that have been discovered in the course of these 

 studies, but it must be realised that the metabolism of the 

 intact cell is far more complicated than any of the separate 

 reactions which can be studied in vitro, as we have not only 

 the interplay of the various enzymes on each other and on 

 the reactions catalysed by each other, but also the effect of 

 environmental conditions on the formation of the enzymes 

 themselves. We shall proceed to the discussion of this aspect 

 of bacterial metabolism in the next chapter. 



