SOME RECENT WORK ON PLANT OXIDASES 113 



It is with some of the more recent results of the study of 

 the oxidases that this paper proposes to deal. The subject as 

 it was known up to 1910 has been exhaustively treated of by 

 Kastle, 1 also by Clark, 2 and Czapek, 3 and to these publications 

 the author is much indebted. 4 



The Nature of Plant Oxidases 



On the whole the substances which effect oxidations in plants 

 have the properties of enzymes, though their behaviour is in 

 some ways peculiar. The usual routine adopted in deciding 

 whether a given reaction is enzymic or an ordinary chemical 

 change is to boil the solution. If the reaction is no longer 

 brought about it is concluded that it is enzymic, its cessation 

 being due to the destruction of a thermolabile oxidising agent. 

 But enzymes have two other very important characteristics, 

 firstly, that a small quantity of the enzyme brings about a 

 relatively enormous transformation of the substrate, and secondly, 

 that the rate of this change is proportional to the amount of 

 enzyme present (provided the substrate is in large excess), 

 though the total amount transformed is independent of it if a 

 sufficient time be allowed to elapse. It may be added that 

 enzymes are colloidal, and the reactions they bring about or 

 catalyse are in many cases proved to be reversible, the point of 

 equilibrium being usually very near that of complete change in 

 one direction. Furthermore their action is as a rule specific, 

 one enzyme only acting on one substrate, or on one class of 

 substrates, and may in many cases be inhibited entirely, or 

 reduced in velocity by very minute quantities of paralysors. 



Now the oxidising substances of plants are destroyed by 

 heat, though in some cases they may be formed afresh within 



1 J. H. Kastle, Bull. No. 59, Hyg. Lab. U.S. Pub. Health and Mar.-Hosp. 

 Serv. Wash. 19 10. 



2 E. D. Clark, Dissertation, Columbia Univ. 1910 (Eschenbach Co., Easton, 

 Pa.). 



3 Czapek, Ergebnisse d. Physiol. 1910, 9, 587-613. 



4 I have followed the custom of the American authors, and of Fowler {Bacterio- 

 logical and E7izyme Chemistry, Arnold, London, 191 1), Moore, and Whitley, in 

 writing " oxidase " rather than " oxydase," to denote the enzyme that splits up a 

 (per)oxide. The spelling " oxydase " has been taken directly from the French, in 

 which both " oxygen " and " oxydant " retain the letter " y." It seems an un- 

 desirable anomaly to spell " peroxide " with " i " and " peroxydase " with " y " as 

 is done at present. " Oxygenase," the enzyme which splits up molecular oxygen, 

 if such an enzyme exists, is of course correctly spelt with "y." 



8 



