428 



SCIENCE 



[N. S. Vol. XLVII. No. 1218 



and also by teeing compounds such as 

 hippuric acids, which do not contain an 

 amino group. 



In these compounds, it is possible that 

 the equilibrium between the keto-lactam 

 enol-laetim forms might be changed rap- 

 idly if the conditions were changed slightly. 

 A more stable substance was therefore 

 studied from this point of view. Imido- 

 esters, as shown by the formula (a), pos- 

 sess the enol-laetim structure in which the 

 hydrogen atoms may be substituted by or- 

 ganic radicals. The hydrolytic actions on 

 esters of ethyl imidobenzoate (6) at differ- 

 ent hydrogen-ion concentrations and vari- 

 ous conditions were measured. 



R — C ( OE') = NE", CoHs — C ( OC^H.) = NH 



(a) (6) 



Finally, in order to reproduce the condi- 

 tions and properties of naturally occurring 

 lipases as far as possible, a number of dif- 

 ferent proteins were treated with alkali for 

 the purpose of producing an enol-laetim 

 grouping in the peptide linking if this were 

 possible, then neutralized to different hy- 

 drogen-ion concentrations and the hydro- 

 lytic actions tested on a number of differ- 

 ent esters. 



As the data obtained have been presented 

 in detail in the papers referred to, they 

 will not be repeated here. It may be stated 

 that the assumption with regard to the ac- 

 tive grouping has been borne out by the 

 experimental facts with the different series 

 of compounds. Especially interesting are 

 the ester hydrolyzing substances obtained 

 by the action of alkali on a number of pro- 

 teins.^' 



It must be emphasized that no direct 

 conclusive evidence is presented as to the 

 actual chemical configuration of the active 



17 F. 



(1917) 



H. Frankel, J. Biol. Chem., Becember 



lipase grouping. The steps in the reason- 

 ing may be summarized as follows: 



Inaetivation (and therefore also activa- 

 tion) is assumed to be due to a tautomeric 

 rearrangement whose possible nature is in- 

 dicated. Simple substances possessing 

 such structures show the actions and some 

 other properties of naturally occurring 

 lipases present in protein materials. Inac- 

 tive proteins treated in such a way as to 

 produce the supposedly active grouping 

 ghow ester-hydrolyzing properties. 



Whether it is possible to go much beyond 

 this in the present state of the knowledge 

 of the chemical nature of proteins and the 

 changes they undergo with simple treat- 

 ment, is an open question. However, one 

 possible line of development bearing di- 

 rectly upon the present problem may be 

 indicated. 



The equilibrium in solution between the 

 tautomeric forms of acetoacetic ester, and 

 also of other substances, depends to a great 

 extent upon the solvent.^^ This suggests 

 that with the enol-ilactim keto-lactam tau- 

 tomerism in proteins, the colloidal proper- 

 ties of the protein material may well exert 

 an influence on the grouping comparable to 

 the effects of the solvent on the tautomer- 

 ism of acetoacetic ester just mentioned. 

 The decreased stabilities or increased rates 

 of inaetivation of enzyme preparations 

 when separated to a greater or less extent 

 from colloidal and other matter not con- 

 nected with the actions may then parallel 

 the actions of the solvents on the equi- 

 libria between the tautomeric forms of 

 acetoacetic ester. 



In the development of the hypothesis re- 

 garding the active grouping in lipase ac- 

 tions, the experimental work and discus- 

 sion was limited almost entirely to the pep- 



18 K. H. Meyer and F. G. Willson, Ber., 47, 832 

 (1914). 



