290 INTRACELLULAR LUMINESCENCE 



of all nonliiminescent reactions, respectively, of FMNH2. The k's stand 

 for specific rate constants of the reactions as indicated. 



With DPNH2 present in excess in the experiments described, its 

 concentration remains essentially constant over short periods of time. 

 When the pressure is changed, the rate constants change immedi- 

 ately, in accordance with the amount of pressure and the respective 

 values of the volume change of activation constants. On the basis of 

 the evidence at hand, fci is characterized by a large volume increase 

 of activation, whereby it becomes smaller, and the steady-state inten- 

 sity therefore lower, under increased pressure. Similarly, ^2 is charac- 

 terized by a small volume decrease of activation, whereby it becomes 

 slightly larger under pressure than at normal pressure, thus giving 

 rise to transitory spikes and dips. (At elevated temperatures the much 

 greater magnitude of the spikes and dips is presumably due to the 

 relation of denaturation equilibria of one or more enzymes to pres- 

 sure.) The rate of change between steady states, with change in 

 pressure, is given by the exponential factor in the following equation, 

 derived in line with the theory of consecutive first order reactions dis- 

 cussed elsewhere (Johnson, Eyring, and Polissar, 1954; Strehler and 

 Johnson, 1954): 



/ = um = M.{rBo] - ^>-<'-"' + jffi; 



In this equation, I represents the intensity of luminescence, b is a. 

 proportionahty constant. Bo is the initial concentration of B at the 

 time when pressure is applied or released, and the k's refer to the 

 reactions as diagrammed above. It will be noted that reactant con- 

 centration does not enter into the exponential factor; the rate of 

 change between steady states is exp. - {ko + h)t equals the slopes 

 of the lines in Fig. 14. Since kn is sensitive to pressure, whereas 

 (^2 + ^3) is not appreciably sei^sitive to pressure, it follows either 

 (1) that ^3 is very much larger than k. or that (2) compensatory 

 changes in fco and ^3 occur under pressure. Of these alternatives, the 

 former appears far more probable. Among other reasons, unless h 

 were much larger than ko, the quantum efficiency would be extraordi- 

 narily high. The nonluminescent, auto-oxidation of reduced FMN 

 probably accounts, in large part, for ^3. 



