CHAPTER IX 



HE MATIN ENZYMES, II 



1. INTRODUCTION 



1.1. Historical 



This chapter will be concerned mainly with the enzymes catalase 

 and peroxidase. In contrast to the cytochrome system these do not 

 react with molecular oxygen, but with hydrogen peroxide, although 

 with certain substrates, peroxidases may behave as oxidases. 



A decomposition of hydrogen peroxide by plant and animal tissue, 

 as well as by certain finely divided metals, was discovered by Thenard 

 in 1811. For many years catalase was confused with peroxidase until 

 the decomposition of hydrogen peroxide into oxygen and water was 

 known to be due to a specific enzyme, which was called catalase by 

 Loew (1772). The similarity of the names catalase and catalyst is 

 not accidental. Bredig's model experiments {3S3) on the catalatic 

 action of colloidal platinum have been of fundamental importance 

 for the development of the theory of catalysis and have stimulated 

 work on the enzymes and the use of inhibitors for enzyme studies in 

 general. The similarity between the mode of action of the enzyme 

 and that of the colloidal metal is, however, probably not as close as 

 was then assumed. 



Peroxidative action of biological material was first observed in 

 1863 by Schonbein (2^54). The name peroxidase was first applied 

 in 1898 by Linossier {1750), but a clear distinction between oxidases 

 and peroxidases was not made until later {Ii.39,521), and in the case 

 of the peroxidase of leucocytes only recently {26). 



In addition to catalases and peroxidases, this chapter will deal with 



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