FRANK H. JOHNSON 273 



trypsin, however, have shown that the value of AV^ in the hydrolysis 

 of synthetic peptides varies with the substrate, and may be negative 

 or zero (VVerbin and McLaren, 1951a,b). 



The observed effect of pressure on the steady-state level of lumines- 

 cence becomes less as the temperature is raised toward the optimum, 

 and at still higher temperatures the level increases, rather than de- 

 creases, under pressure. The family of curves in Fig. 5A resembles a 

 family of curves obtained by Professor D. E. Brown (cf. Johnson, 

 Eyring and Polissar, 1954) for the tension of auricle muscle as a 

 function of temperature and pressure. 



Figure 5B shows that the observed effect of pressure at a given tem- 

 perature depends upon the specific biological system involved. The 

 three species represented in this figure normally exhibit different tem- 

 perature optima for luminescence, i.e., around 20° in P. phosphoreum, 

 26° in A. fischeri, and 30° C in A. harveyi. In each case, the effect of 

 pressure is in accordance with what one would expect on the basis 

 that pressure diminishes the intensity of luminescence at temperatures 

 below that of the specific optimum and augments the intensity at 

 temperatures above the specific optimum, with little effect at the op- 

 timum. A pressure-temperature relationship of this kind was first rec- 

 ognized by Brown (1934; 1934-35) in studies with muscle. 



Volume Change of Reaction (aV) in Reversible Denaturation 



The opposite effect of pressure at high and low temperatures, re- 

 spectively, as illustrated in Fig. 5A, shows that the limiting reactions 

 are not the same at these different temperatures. Since the increase in 

 steady-state luminescence under pressure becomes greater as Ki of 

 the reversible denaturation becomes greater with rise in temperature, 

 the simplest interpretation is that pressure causes a partial reversal 

 of the denaturation of the enzyme involved. In other words, the 

 equilibrium change from native to reversibly denatured forms of the 

 enzyme is accompanied by a volume increase of reaction. The data 

 indicate that the value of aV in this reaction amounts to about 65 cc 

 per mole at 35° C. 



If we assume as before that there are two reactions primarily limit- 

 ing the overall luminescent reaction, viz., the catalytic reaction of a 

 limiting enzyme and the reversible denaturation equilibrium, tem- 



