248 



SCIENCE 



[N. S. Vol. XXVII. No. 



ments hold for the ordinary changes of 

 tissue metabolism in animals and plants, 

 but in that more or less hidden world 

 of microorganisms so potent for good and 

 evil, tangible enzymes are likewise re- 

 sponsible for many, if not all, of the chem- 

 ical reactions by which the life and 

 activity of the organisms are mani- 

 fested. New enzymes and new forms of 

 chemical change are constantly being dis- 

 covered and as a result new light is be- 

 ing thrown upon many phases of tissue 

 metabolism and the processes connected 

 therewith. 



Note, for example, the group of unique 

 enzymes concerned in the transformations 

 of nueleoproteins ; enzymes which are 

 widely distributed among different species 

 of animals, in different organs and tissues, 

 and which are truly unique in the character 

 of the chemical changes they are capable of 

 producing. Thus, we have nuclease, which 

 splits off or liberates the purines from the 

 nucleic acid complex ; adenase and giianase, 

 deamidizing enzymes which are able, by 

 hydrolysis with liberation of ammonia, to 

 form the oxypurines hypoxanthine and 

 xanthine from the aminopurines adenine 

 and guanine; xantho-oxidase, which by 

 oxidation transforms the oxypurines to 

 uric acid; and lastly, a uricolytic enzyme 

 which is able to accomplish the destruction 

 of uric acid with formation of allantoin as 

 one of the intermediary products. Ob- 

 serve how these successive steps in the 

 formation of uric acid from a nucleoprotein 

 are accomplished by specific enzymes, each 

 one of a distinct type and limited in its 

 action to the one transformation. Further, 

 it has been found by several observers that 

 these characteristic enzymes are not com- 

 mon to all active tissues; different organ- 

 isms shoAV unlike equipment in this respect, 

 thus indicating, as a recent writer has ex- 

 pressed it, that there are "noteworthy 

 variations in the purine metabolism of dif- 



ferent species."' Consider also arginase 

 which has the power of effecting the 

 hydrolysis of arginine, with production of 

 urea and ornithine; an enzyme present in 

 the liver, kidneys, thymus, intestinal 

 mucous membrane and other tissues, as 

 well as in yeast. Her-e is an enzyme, ac- 

 cording to Dakin,° which is adapted for 

 the exclusive hydrolysis apparently of 

 dextro-arginine or of other substances con- 

 taining the dextro-arginine grouping, and, 

 as in the case of glucosides and sugars, the 

 relation of the enzyme to the substrate is so 

 intimately and finely adjusted that many 

 other substances structurally similar to 

 arginine are incapable of hydrolysis by 

 arginase. Note likewise the newly dis- 

 covered enzymes creatinase and creatin- 

 inase,^" the former of which is apparently 

 able to transform creatin into creatitiin, 

 while the latter is said to decompose 

 creatinin, presumably into methyl glyeocoU 

 and urea. 



Truly, we have in the action of these 

 peculiar enzymes a striking] illustration of 

 how in intermediary tissue metabolism 

 successive chemical transformations may be 

 accomplished in orderly fashion, while at 

 the same time there is suggested the prob- 

 able existence of many other specialized 

 enzymes capable of inciting chemical reac- 

 tions of equal interest. Is there not pos- 

 sible gain to be had in a broader, more com- 

 prehensive study of the intracellular 

 enzymes of animal tissues? Doubtless in 

 each species of animal there are peculiari- 

 ties of metabolism which are truly specific ; 

 probably also there are specific enzymes, 

 the presence and action of which are the 

 determining factors in the special line of 



' Mendel and Mitchell, American Journal of 

 Physiology, Vol. XX., p. 100, 1907. 



° Journal of Biological Chemistry, Vol. III., p. 

 435, 1907. 



" Zeifschrift fiir physiologischen Chemie, Band 

 LII., p. 1, 1907. 



