ROLE OF REDUCTASE IN TISSUE RESPIRATION 65 



haemoglobin to the completely reduced condition, and since it 

 carries oxygen from it in this way it is, in one sense, an 

 " oxygenase." It is quite possible that the " organic peroxide 

 plus ferment " of certain writers is none other than our hsemo- 

 globinase, which is certainly of colloidal nature. There seems 

 no need of retaining the term oxygenase when haemoglobinase 

 is a more specific term for a ferment which can do all that 

 oxygenase is supposed to do and considerably more. 



We have seen that reductase is very insoluble ; the true 

 meaning of this may be that what we call reductase is in ultimate 

 cellular analysis the totality of certain side-chains of the living 

 protoplasmic molecule (biogen) which possess affinities for 

 oxygen. These, in the nature of things, cannot be disrupted 

 from the biogen without compromising its functional integrity. 

 This sort of thing in ultimate analysis an cndo-enzyme proves 

 itself to be; and Vernon has indeed remarked on the insolu- 

 bility of certain oxidases. 



It is true that on this view the distinction between "vital 

 protoplasmic activities " and enzymes is obliterated, but it is 

 quite possible that that distinction has been made too absolute. 

 When an exo-enzyme or enzymic secretion, such as ptyalin or 

 pepsin, can perform its function equally well in the cavity of a 

 viscus or in vitro, we may be justified in maintaining the distinc- 

 tion between vitality and enzymic action. The secretion-enzyme 

 was, however, part of the protoplasmic molecule before its separa- 

 tion. It is not the act of disrupting the side-chain that constitutes 

 an enzyme ; doubtless disrupted side-chains are our separable 

 ferments, and, because disrupted, are more or less soluble. But 

 non-separated side-chains can still be called ferments (endo- 

 enzymes), which because undisrupted are " insoluble." The 

 former — the secretion-enzymes — are destined to leave the parent 

 protoplasm ; the latter are not intended to be separated from the 

 biogens and are, therefore, called endo-enzymes. It is not 

 whether they act outside or inside the protoplasm that constitutes 

 them ferments, it is their functional powers that confer the title 

 on them. Since animal heat is genetically an intracellular affair, 

 the ferments haemoglobinase and the oxidases, which are con- 

 cerned in its evolution, are therefore also intracellular. The 

 former is non-specific, the latter highly specific ; the former is 

 for obtaining oxygen wherever available, the latter are specialised 

 each for the oxidation of only one kind of substance. 

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