188 COLLOIDS IN BIOLOGY AND MEDICINE 



He says "The degree to which acetyl cellulose swells, runs parallel 

 with its speed of saponification by aqueous alkalis, so that with 

 greatly swollen acetyl celluloses the saponification by 1/2 n KOH is 

 completed quantitatively in a few hours, at room temperature." 



We have not yet answered the question : What property is to be 

 ascribed to the specific action of enzymes? We may regard this 

 query as being answered by G. BREDIG and FAJANS* as far as the 

 principle involved is concerned. They demonstrated that right 

 and left campho- and bromo-campho-carbonic acid (which resemble 

 one another like a picture and its reflection in a mirror) may be 

 split into camphor and carbonic acid by bases acting as catalyzers. 

 The speed with which these two opposites are broken down differs 

 considerably if optically active bases (quinine, quinidine, nicotine 

 and cinchonine) are employed, and may amount to 50 per cent. 

 This is analogous to the specific action of enzymes upon chemically 

 known substances with catalyzers which have definite chemical 

 characteristics. It has been shown for most enzyme actions, with 

 certain exceptions among the sugars, that of two optically active 

 isomers both are attacked by a given enzyme, but one is always 

 affected more quickly. We thus have a complete analogy for natural 

 enzymes, but beyond this point the "lock and key" idea fails, since 

 under no circumstances could "an asymmetric key fit the mirror 

 image of its proper lock." 



But the analogy extends further. G. BREDIG and FISKE effected 

 asymmetric synthesis by a catalyzer of known composition. According 

 to L. ROSE-NTHALER, the enzyme action of emulsin accelerates the 

 following reaction: 



C 6 H 5 - CHO + HCN = C 6 H 5 CH(OH) CN. 



Benzaldehyde -j- hydrocyanic, nitromandelic acid, 



acid 



G. BREDIG and FISKE replaced emulsin with quinine, but if they 

 employed chinidin as a catalyzer they obtained laevo rotary nitro- 

 mandelic acid in addition to the inactive product. 



We may summarize our present understanding of enzyme action 

 thus: As a result of their colloidal properties, under favorable ex- 

 ternal circumstances, enzyme and substrate are greatly concentrated 

 at their interfaces, so that the course of the reaction is very much 

 accelerated; the reaction between enzyme and substrate is purely 

 chemical, conditioned by their mutual chemical constitution or con- 

 figuration. [Ultramicroscopic observations suggest that possibly 

 physical action is also involved. J. ALEXANDER, Jour. Am. Chem. 

 Soc., 1910, vol. 32, p. 680. Tr.] 



Enzymes, perhaps, exhibit the property of aging to a greater ex- 

 tent than all other colloids. Some, e.g., trypsin, if dried, lose their 



