XU INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



out, on the basis of the theory of absolute reaction rates and ordinary 

 equilibrium theory, which though admittedly oversimplified accounted 

 for the data on luminescence with considerable success. The hypothesis 

 included some new concepts, e.g. that the thermal denaturation of proteins 

 is subject both to retardation in rate and to reversal by hydrostatic pres- 

 sure (accounted for in terms of large, molecular volume increases of acti- 

 vation and of reaction, respectively) ; that the thermal denaturation equi- 

 librium is involved in the physiological effects of certain narcotics, whose 

 action consists, in part, in promoting the reversible and irreversible de- 

 naturation of a key enzyme system; that enzyme reactions may be ac- 

 companied by large ^•olume changes of activation; and that the optimum 

 temperature of a biological reaction occurs at a point where the effect of 

 heat in accelerating enzyme activity is balanced by the effect of heat in 

 promoting reversible enzyme denaturation. In terms of this hypothesis, 

 several phenomena became understandable, e.g. the inhibitory action of 

 pressure at low temperatures (relative to the specific optimum) where 

 the denaturation equilibrium is normally not significant; the favorable 

 action of pressure at high temperatures, where a large proportion of limit- 

 ing enzyme exists in a catalytically inactive state that is reversible by 

 pressure ; the reversal of narcotic action by pressure ; the reversible changes 

 in the observed rate of the over-all process at normal pressure, i.e. the 

 temperature-activity curve, over a broad range of temperatures from well 

 below to considerably above the optimum temperature; and the changes 

 in the net effects of pressure at a series of constant temperatures below, 

 at and above the optimum. 



Although the hypothesis arrived at through studies of bacterial lumi- 

 nescence was initially based on purely kinetic evidence pertaining to a 

 process in intact, living cells, investigations of other systems and through 

 other approaches have provided further evidence consistent with the origi- 

 nal views. For example, the thermal denaturation of pure proteins in 

 solution has been shown, both in this country and abroad, to be retarded 

 by increased hydrostatic pressure. Perhaps the most remarkable example 

 has to do with the relation between hydrostatic pressure and narcosis: 

 tadpoles immersed in narcotizing concentrations of alcohol or urethane 

 have been observed to recover their activity under increased pressure 

 (Johnson et al., 1950-51), and single nerve cells rendered inexcitable by 

 these same drugs recover their excitability under increased pressure (Ta- 

 saki and Spyropoulos, this volume). 



Other aspects of the research on luminescence, however, are more im- 

 portant than whether or not the original hypothesis has been justified in 

 its various details by subsequent investigations. First of all, it brought 



