Mat 3, 1918] 



SCIENCE 



425 



IV. Adsorption is one of the controlling 

 factors in the kinetics of invertase action, 

 and the velocity of inversion curve has the 

 same general shape as adsorption curves, 

 as suggested by Henri. 



This brief review will show the uncer- 

 tainty of the conclusions from the results 

 obtained in the study of the kinetics of one 

 of the most carefully measured of enzyme 

 actions. The factors controlling the veloc- 

 ity of this reaction are just beginning to be 

 cleared up, the simple earlier views being 

 incomplete. 



An unsuccessful attempt to formulate 

 the kinetics of enzyme action in a compara- 

 tively simple way may be mentioned. The 

 hydrolj'sis of urea to foi-m ammonia and 

 carbon dioxide was used by D. D. van 

 Slyke^^ to develop a general theory of the 

 kinetics of such enzjTne actions based upon 

 the assumption of an intermediate com- 

 pound between enzyme and substrate. Un- 

 fortunately, in the development of the 

 equations a further assumption was intro- 

 duced which limits their validity and appli- 

 cabilitj- to definite conditions which are 

 realized only in special cases.^* 



The study of the kinetics of enzyme ac- 

 tion has not, therefore, led to any results 

 with regard to the chemical nature of 

 enzymes, even in the simplest cases of chem- 

 ical changes. Practically all enzymes are 

 colloids, and when the substrate also is a 

 colloid, as in the action of a protease on a 

 protein, it is obvious that the conditions are 

 complicated to such an extent that a quan- 

 titative study of the kinetics of such a re- 

 action appears to be almost hopeless, al- 

 though valuable qualitative resiolts may be 

 obtained. 



The study of the chemical nature of 

 enzj-mes is complicated in most cases by 



13 D. D. Van Slyke and G. E. CuUen, /. Biol. 

 Chem., 19,146 (1914). 



i*J. Biol. Chem., 28, 389 (1917) . 



reason of the complexity of the substances 

 whose changes they accelerate. This diffi- 

 culty can be obviated for a few of the 

 enzymes. For example, the lipases and 

 esterases accelerate the hydrolysis of fats 

 and esters. "While the mechanism of the 

 hydrolysis of an ester to form acid and al- 

 cohol in the absence of lipase is not known 

 definitely, still the compositions and prop- 

 erties of the initial and final products 

 undergoing the enzymatic change are 

 known. This eliminates, partly at any 

 rate, one of the unknown factors of the 

 enzyme problem, and is the main reason 

 for studying lipase in connection with the 

 question of the chemical nature of the ac- 

 tive catalyst, the enzyme. 



Practically all enzj-mes are colloids or 

 are intimately associated with substances 

 having colloidal properties. Furthermore, 

 in a large number of cases, it seems that the 

 enz3-me is associated with protein matter, 

 either as an essential part of the protein 

 molecule, or aceompanj'ing it in such a way 

 that separation has not yet been effected. 

 Among the enzymes which chemically show 

 the characteristics of proteins may be men- 

 tioned the amylase obtained by Sherman," 

 proteases and lipases. On the other hand, 

 the invertase described by Nelson" is a 

 carbohydrate phosphoric acid complex con- 

 taining about one per cent, of nitrogen in 

 the form of protein. 



These facts make it evident that for the 

 case of lipase, to use a specific example, the 

 isolation of the enzjone in a pure state is 

 a phase or part of the problem of the isola- 

 tion of a pure protein, since in the separa- 

 tion of the active lipase from inactive ma- 

 terial present with it, the resulting bodies 

 approach more and more nearly in proper- 



15 Sherman and coworkers, J. Am. Chem. Soc., 

 1912-1917. 



i« Nelson and Born, /. Am. Chem. Soc, 36, 393 

 (1914). 



