ENZYMES 



59 



(products) are present in solution in greater than equilibrium concentra- 

 tions, the reactants combine with the enzyme, unite, and diffuse away. 

 Figure 11 gives a diagram which is helpful in visualizing these processes. 



ADAPTIVE ENZYMES 



Some fungi produce certain enzymes only in response to particular 

 environmental conditions. Such enzymes are called adaptive enzymes. 

 \\^ether they are produced under all cultural conditions, but in such small 

 amounts as to be undetectable, or whether they are produced de novo is 

 questionable. How^ever, this phenomenon is of great importance. Two 

 types of behavior may be noted when a fungus is placed upon unsuitable 

 medium for the first time. Either the fungus may die, owing to lack of 

 ability to synthesize the enzymes to cope with the new environment; or 



240 



160 



co^ 



80 



Strain CI 



-d^ 



^-0- 



o -Aerobic adaptation 

 • -Anaerobic adaptation 



■4-1-* I * ■ 



_1_ 



./ 



8 



16 



32 



40 



24 

 Hours 

 Fig. 12. Rate of adaptation of a strain of Saccharomyces carlsbergensis to galactose 

 under aerobic and anaerobic conditions. (Courtesy of Spiegelman, Jour. Cellular 

 Comp. Physiol. 25: 128, 1945. Published by permission of Wistar Institute of 

 Anatomy and Biology.) 



after a time it may synthesize the necessary enzymes, and the fungus is 

 then able to grow and function under the new surroundings. Wlrether or 

 not the fungus is able to synthesize "new" enzymes depends upon its 

 genetic constitution. The biochemical and physiological responses of an 

 organism may change when it is placed on a different kind of medium. 

 These changes ordinarily are called forth by deficiencies in the medium. 

 The substrate upon which the inoculum grew- may be very important in 

 governing the various responses of the organism. 



Spiegelman (1945) has shown that the adaptation of yeasts to galactose 

 is affected by aerobic and anaerobic conditions. Adaptation is more 

 rapid in air than in nitrogen, and some strains of yeast are unable to adapt 

 to galactose in the absence of oxygen. Figure 12 shows that only some 

 30 min. is required for Saccharomyces carlshergensis to begin to utilize 

 galactose under aerobic conditions, while about 20 hr. are required under 

 anaerobic conditions. 



The effect of composition of the medium on the readaptation of panto- 



