EFFECTS OF TEMPERATURE: CELLULAR SYSTEMS 789 



It is also not known with which components of the total system inhibitors 

 such as sulfanilamide and urethane react. It is true that urethane and sul- 

 fanilamide have been found to inhibit reversibly the Cypridiyid luciferin- 

 luciferase reaction iu vitro (Johnson and Chase. 19J:2), but it would seem 

 that this enzyme is generally less sensitive than the i» vivo systems and it 

 is quite possible that other reactions are depressed in the living cell. It 

 is well known that both urethane and sulfanilamide inhibit pathways other 

 than those of luminescence. In interpreting temperature studies it is im- 

 portant to know whether one system only or several pathways are affected. 

 It is unfortunate that temperature studies have not been done on the in- 

 hibition of the purified enzyme system. It would also perhaps be interesting 

 if Johnson and his group had used some of the better known inhibitors 

 whose actions are more specific and characterized. Urethane particularly 

 is quite nonspecific at the high concentrations used in the luminescence 

 studies. Of course, denaturing agents are never specific. 



The intensity of luminescence in certain species probably depends, for 

 one thing, on the concentration of ATP (Harvey, 1960), which may be mod- 

 ified by inhibition exerted either on the systems forming ATP or utilizing 

 ATP. Temperature optima may occur for the ATP concentration because 

 of different temperature coefficients for the forming and utilizing reactions. 

 The presence of an inhibitor may change these optima because of differential 

 effects on these reactions, and consequently the T„^,, for the metabolic or 

 functional reactions dependent on ATP may be shifted. In other words, it 

 is possible in a complex metabolic system to explain a shift in the T,,^^, 

 by assuming differential effects of the inhibitor on the reactions of the multi- 

 enzyme system, rather than by the altered action of the inhibitor on a single 

 enzyme component of the system. In the case of bacterial luminescence it 

 is very difficult to say if the temperature dependence of inhibition is re- 

 lated to a single enzyme or to more complex changes in a multienzyme sys- 

 tem. Since the concentration of the intermediate B in the simple irreversible 

 monolinear chain: 



is given by: 



Ki E., 



A -» B -^ C 



(B) = KM[V .JV^__ 



which is modified from Eq. 7-3. and since temperature changes or inhi- 

 bitors can alter K^, K.,. Fj, or Fg in different ways, it is quite possilbe 

 for (B) to show shifts in the T„^^, during the inhibition, or to show effects 

 of temperature on the inhibition. The same principles would apply to other 

 more complex multienzyme systems, as has been discussed earlier in this 

 chapter. For example, it may be easily shown from the above equation that 



