EFFECTS OF TEMPEEATURE: MULTIENZYME SYSTEMS 771 



ways that are convergent, as well as other types of multienzyme systems 

 which behave in a similarly complex manner, and this frequently makes 

 it impossible to assign the results from temperature studies to any one 

 reaction step. 



It is obvious that when E^ is selectively inhibited, the depression of 

 the formation of C will depend on the relative contributions of reaction 1 

 and reaction 3 to the production of B, and that if temperature changes 

 this relative contribution, the over-all inhibition will be altered (Eq. 7-24). 

 Inhibition of one of the feeding reactions will also modify the response of 

 the system to temperature change, since this response depends on the rela- 

 tive contributions of reaction 1 and reaction 3. 



(C) Divergent chains. Here the result will depend on which product is 

 determined. A change of the temperature may shift the ratio of v^jv^, 

 i.e., the fraction of B that goes to each product may be changed. It is 



El ^2 C 

 A ^ B (^ (15-42) 



even possible that an increase in the temperature will decrease the rate at 

 which one of the products is formed, due to the other reaction having a 

 relatively high temperature coefficient. If one is primarily interested in 

 reaction 2, its rate at the control temperature is given by v.2 = i\ — v^ 

 and at the altered temperature by g.^v^ = g]V■^^ — g^v^, assuming a steady 

 state. Thus the factor by which reaction 2 is changed by the temperature 

 variation is given by: 



g^ = (15-43) 



i\ - V3 



It is true that these relationships are very simple, and perhaps obvious to 

 some, but they have generally been ignored by those studying the effects of 

 temperature on metabolism. 



If an inhibitor acts selectively on E3, the fractional stimulation of Vg 

 will be i^vjv^. At another temperature the stimulation of Vg will be given 

 by hg-iV^jg^v.^. Thus the degree to which reaction 2 is stimulated by the 

 inhibitor will depend on ^3/^2- the ratio of the temperature effects on these 

 two reaction rates, as well as on any alteration of the inhibition of reaction 

 3 by the temperature change. The steady state concentration of B depends 

 on 7i, F2, F3, K^. Ko, and K^ (Eq. 7-27) in the uninhibited system and. 

 in addition, on K^ in the inhibited system, so that the inhibition of any 

 step will alter (B) to a degree dependent on the temperature in a complex 

 fashion, since all of these constants may vary with the temperature. 



