ENZYMES. OXIDASES. 11 



the greatest importance. The catalysts, like the enzymes, are not found 

 in the final products of the reaction, they are not used up in the process, 

 and the quantity of the active substance proportionate to the quantity 

 of substance transformed is infinitesimally small in enzyme action as well 

 as in catalysis. Without having positive proof, nevertheless we now 

 consider that enzyme action is not to be considered as the starting of a 

 reaction which would not of itself take place, but rather as an accelera- 

 tion of a slowly proceeding, often not noticeable, chemical change. 

 According to this conception enzyme action comes in line with catalysL, 

 as understood to-day (see Chapter II). 



An enzyme is an organic substance formed in an animal or plant 

 cell, which is destroyed by heating its aqueous solution and which acts 

 like the catalytes, but only upon certain bodies. Some restriction must 

 be put to this, as the cells do not always produce a complete enzyme, 

 but more often only the mother-substance thereof. These mother-sub- 

 stances of the enzymes are called proenzymes or zymogens. The zymogens 

 are under certain conditions converted into enzymes, and in certain cases 

 this is brought about by the special action of bodies called kinases, 

 which have been little studied (see Chapter II, VI and IX). 



According to their action most of the enzymes which have been 

 studied may be divided into two chief groups, namely, those having a 

 hydrolytic action and those having an oxidizing action. 



After this short discussion of the enzymes we can now return to the 

 oxidations and the so-called oxidation ferments. 



It has also been positively proven by the researches of JAQUET, 

 SALKOWSXI, SPITZER, ROHMANX, ABELOUS and BIARNES, BERTRAND, 



BOURQUELOT, DE REY-PAILHADE, MEDWEDEW, PoHL, JACOBY, CHODAT 



and BACH 1 and others that in the blood and different tissues of the ani- 

 mal body, as also in plant-cells, substances occur which have the prop- 

 erty of causing certain oxidations. For this reason these bodies have 

 been called oxidases, and they have been divided into two different 

 groups. The ferments of the first group, called primary or direct oxidases, 

 or simply oxidases, transfer the oxygen of the air directly to other 

 bodies. Those of the second group, the indirect oxidases or peroxidases, 

 are active only in the presence of a peroxide, as they set oxygen free 



1 Jaquet, Arch. f. exp. Path. u. Pharm., 29; Salkowski, Centralbl. f. d. med. Wis- 

 sensch., 1892 and 1894, and Virchow's Arch., 147; Spitzer, Pfliiger's Archiv, 60 and 

 67; Spitzer and Rohmann, Ber. d. deutsch. chem. Gesellsch., 28; Abelous et Biarnes, 

 Arch, de physiol. (5), 7, 8, and 9, and Compt. rend. soc. biol., 46; Bertrand, Arch, de 

 physiol. (5), 8, 9, and Compt. rend., 122, 123, 124; Bourquelot, Compt. rend. soc. 

 biol., 48, and Compt. rend., 123; Medwedew, Pfliiger's Arch., 81; Jacoby, Ergebnisse 

 der Physiologic, Jahrg. I, Abt. 1, which contains the literature of the subject; Chodat 

 and Bach, 1. c. 



