42 ENZYMES AND ENZYM1C ACTIVITIES OF FUNGI 



different enzymes. Some behave catalytically in rendering oxygen 

 active; others seem to function as carriers of oxvgen, of hydro- 

 gen, or of phosphates. 



Specificity of enzymes. Much of the classification of enzymes 

 is based upon the assumption that each enzyme can act upon a 

 single definite chemical compound. In order clearly to compre- 

 hend this interpretation, the lock and key analogy has been 

 widely employed to illustrate enzyme specificity. The substrate 

 is analogous to the lock, and the enzyme to the key. A certain key 

 is required to turn each lock, and hence a certain enzyme to de- 

 compose each substrate. This analogy is very serviceable but 

 conveys the implication that certain enzymes may be master 

 enzymes, since they act as master keys. Zymase, for example, 

 can decompose the four stereoisomers J-glucose, J-mannose, 

 J-levulose, and J-^alactose. Similarly maltase will hydrolyze the 

 a-methvlo-lucosides, and emulsin, the #-methvlo;lucosides, but re- 

 ciprocally these two enzymes are without hydrolytic ability. 



Attention may well be called to the fact that different enzymes 

 may produce different end-products from the same substrate. If 

 the trisaccharide raffinose, for example, is decomposed by inver- 

 tase, melibiose and fructose are formed; if by emulsin, sucrose 

 and galactose. The fact that emulsin may be a complex of sev- 

 eral enzymes may account for this result. Similarly there is evi- 

 dence that amylase, zymase, and tryptophanase are not single 

 enzymes but enzyme complexes or systems. 



Influence of reaction, temperature, and time. In the light 

 of our knowledge of the chemical nature of enzymes and of the 

 modifying effects of pH, temperature, and time on chemical syn- 

 thesis and analysis in general, it should be unnecessary to elaborate 

 on this subject as applied to enzymic reactions. These three en- 

 vironmental factors are minutely correlated, and none operates 

 independently of the others. Each enzyme reacts best under a 

 definite environmental set-up. With time and temperature con- 

 stant pepsin shows its optimum activity 7 in a solution of approxi- 

 mately pH 2.5, whereas trypsin manifests its greatest activity at 

 approximately pH 8.0. With pH and time constant, amylase 

 shows greatest activity not at body temperature but at 60° C. It 

 would be anticipated that enzyme activity would double within 

 a limited range for a 10° rise in temperature, as is postulated in 

 van t Hoffs law. 



