CHAPTER VIII 



HEMATIN ENZYMES, I. 

 THE CYTOCHROME SYSTEM 



INTRODUCTION 



It is beyond the scope of this book to discuss the whole field^ of 

 biological oxidation, or even all known biological reactions in which 

 hematin catalysts have been shown to take part. For this the reader 

 is referred to special textbooks and reviews (14.79,3079,2225,3160) and 

 also to the chapters on biological oxidation and reduction in various 

 volumes of the Annual Review of Biochemistry. In this and in the 

 succeeding chapter we are mainly concerned with the respiratory 

 catal^^sts as characteristic hematin compounds and as peculiar hemo- 

 proteins. We shall try to correlate the little we know about their 

 structure with their biological function, and the chemical reactions 

 on which this function is based with similar reactions of other hematin 

 compounds. In a decade or so it may be necessary to give to each of 

 the hematin enzymes as much space as to the hemoglobin ; later again 

 it may become possible to treat all hemoproteins together from one 

 particular physicochemical aspect. At present the scantiness of the 

 available data does not necessitate the first treatment and excludes 

 the second. 



Only the iron compounds of porphyrins have been shown to possess 

 strong catalytic powers as oxidases, peroxidases, or catalases. Copper 

 porphyrins, for instance, are not stronger oxidative catalysts than 

 ionic copper (24-22). 



We shall discuss in this chapter the cytochrome system, and in 

 Chapter IX the other hematin enzymes, particularly catalase and the 

 peroxidases. 



Role of the Specific Protein. The important role which hematin 



337 



