28 BACTERIAL ENZYMES 



combinations of the enzymes of the organism and their inter- 

 play with the external environment. 



THE STUDY OF ENZYMES IN BACTERIA 



When organisms are growing in a medium, their chemical 

 activities involve the building of cellular material and the 

 breakdown of substances in the medium ; thus we may have 

 one sort of protein being hydrolysed outside the growing cell 

 and another sort being synthesised within the cell. The 

 number of enzymes concerned may be very great and their 

 integrated activities too complex to disentangle. The first 

 step in the simplification of the system is to eliminate synthetic 

 reactions by preventing growth ; this is performed by removing 

 the cells from the growth medium, washing them free from 

 traces of medium, and then suspending the washed cells in 

 distilled water or a suitable salt solution. Investigations of 

 the activity of bacterial enzymes are usually carried out in the 

 first place with such " washed suspensions." Bacteria are 

 seldom susceptible to osmotic rupture when suspended in 

 water, and washing the cells in water often has no deleterious 

 effect upon their chemical activities, but if the properties of 

 the cell-wall are involved in these activities, then it is preferable 

 to wash the cells in a salt solution of composition similar to 

 that of the medium in which they were grown. Since many 

 organisms retain their enzymic activities unimpaired in such 

 " washed suspensions " they can be used for the investigation 

 of metabolic changes, and the system further simplified by 

 incubating the suspension with a single substrate in the 

 presence of a known buffer solution. It does not follow that 

 washed suspensions can be used to study all the enzyme 

 systems of an organism, as it is sometimes found that some 

 activities " decay " rapidly after, or during, the preparation of 

 the suspension. It is seldom that suspensions can be kept in 

 an active state for more than twenty-four hours, although some 

 enzymes, e.g. formic dehydrogenase, will remain active for 

 weeks even in autolysing suspensions. 



