102 growth: synthesis of bacterial protoplasm 



cells grown in medium A, rich in pyridoxin; cells grown in 

 medium B, containing just sufficient pyridoxin to allow full 

 growth; and cells grown in medium C, which is deficient in 

 pyridoxin to such an extent that the growth is seriously 

 restricted by the pyridoxin deficiency. If we investigate the 

 activity of the two enzymes, tyrosine decarboxylase (p. 168) 

 and transaminase (pp. 93-4), in the three cultures, we find that 

 both enzymes are fully developed in culture A ; in culture B 

 the transaminase system is fully developed, but the 



PYRIDOXIN CONTENT OF MEDIUM 



Fig. 8. Relation of growth of streptococci to 

 pyridoxin content of growth medium. 



decarboxylase has about 5 per cent of the activity of culture A ; 

 in culture C the transaminase activity is considerably less 

 than that of cultures A and B, and no decarboxylase activity 

 is demonstrable. If, however, we take the cells from cultures 

 B and C and re-estimate their activities in the presence of 

 added pyridoxal, we find that both the tyrosine decarboxylase 

 and transaminase activities are restored to normal. This 

 suggests that the organism has synthesised the protein portions 

 of the enzymes in all three cultures, but that the enzymes are 

 inactive in the absence of their prosthetic groups or coenzyme 



