STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 



145 



properties. Structures of these compounds and their activities are given in 

 formula (IX). 



CH,OH 



O OCH^ 



Methyl jS-D-galactoside 



is hydrolyzed, 



is inducer. 



CH,OH 



SCH^ 



Methyl jS-D-thiogalactoside 



is not hydrolyzed, 



is inducer. 



CH.OH 



CH,OH 



O — ^ 



Phenyl -j8-D -galactoside 



is hydrolyzed, 



in a weak inducer. 



q s — ( 



Phenyl -j8-D -thiogalactoside 



is not hydrolyzed, has a strong 



affinity for the enzyme, 



is not an inducer. 



(IX) 



It may be noted that although the phenylthiogalactoside is not an inducer 

 in E. coli, it is an inducer oi B. megatherium (Landman, 1957). In this organ- 

 ism, however, as in E. coli, the types of inducers suggest that inducer action 

 depends on a combination with the enzyme-forming system rather than with 

 the enzyme. 



Using the penicillinase-forming system of B. cereus, Pollock (1950) was 

 able to show that the induction of enzyme production was a catalytic 

 phenomenon. In this system S^^-labeled penicillin was fixed specifically by 

 the bacteria at 0°C. to the extent of about 80 molecules per cell. Such ceUs 

 coidd be w; shed free of exogenous peniciUin and would produce penicillinase 

 at a constant rate in the presence of oxygen, glucose, and amino acids. This 

 is the only instance known in which the presence of free inducer is not 

 necessary for continued enzyme production; in other cases enzyme produc- 

 tion stops when inducer is removed. The penicillinase was purified and its 



