34 



BACTERIAL ENZYMES 



In the latter case it probably reacts with the — NHg group 

 of an amino-acid and is converted to pyridoxamine phosphate, 

 leaving the keto-acid corresponding to the amino-acid. 

 Pyridoxamine phosphate can then react with a suitable 

 keto-acid converting it to the corresponding amino-acid 

 while being itself restored to the pyridoxal form. 



Haematin 



HOOC.CH2.CH2 



HOOC.CH2.CH2 



CH=CH2 



CH=CH. 



This forms the prosthetic group of haemoglobin and of enzymes 

 such as catalase, peroxidase, and cytochrome oxidase. Side 

 chains may differ in different enzymes, etc. 



Metals 



Some enzymes contain a metal in their structure, while 

 others are activated by the presence of metal coenzymes. 

 Thus phosphatase is activated by magnesium ions, while in 

 other cases metals such as copper (polyphenol oxidase) or 

 zinc (carbonic anhydrase) appear to be an essential part of 

 the enzyme structure. 



PROSTHETIC GROUPS OF INCOMPLETELY 

 DETERMINED STRUCTURE 



Coenzyme A 



Lipmann, in the course of studies on the acetylation of 

 sulphanilamide by pigeon liver, discovered that the acetylase 

 involved possessed a prosthetic group which could not be 



