284 INTRACELLULAR LUMINESCENCE 



identifying biochemically certain components of the luminescent sys- 

 tem, as well as of purifying the enzymes involved. Rapid progress has 

 already been made toward the latter objectives ( Cormier and Strehler, 

 1953; McElroy et al, 1953, 1954; Strehler et al, 1954; Strehler and 

 Cormier, 1953). 



For the remainder of the present discussion, it is appropriate to 

 dwell on results that have been obtained in a joint study ( Strehler and 

 Johnson, 1954) of pressure-temperature-inhibitor relationships of bac- 

 terial luminescence in cell-free extracts. 



Kinetics of Bacterial Luminescence in vitro 



The observations described in the following paragraphs were made 

 with extracts of A. fischeri cells, prepared by treating first with cold 

 acetone, and then taking up the dried powder in distilled water, fol- 

 lowed by high-speed centrifugation to remove all particulate matter. 

 The supernatant provided a stock enzyme solution which was diluted 

 with phosphate buffer at neutral pH as needed. The addition of fla- 

 vine mononucleotide (FMN), didhydrodiphosphopyridine nucleotide 

 (DPNH2), and decaldehyde in final concentrations of approximately 

 0.3 microgram, 1 mg, and 7 micrograms per milliliter, respectively, 

 gave a "saturated system" that emitted a bright luminescence over 

 extended periods of time at room temperature. 



Figure 12 illustrates the changes in intensity of the saturated system 

 after the sudden application and sudden release, respectively, of hy- 

 drostatic pressure at temperatures below, above, and near that of the 

 optimum (about 26° C) of the system used. One curve (16°, Cells), 

 obtained with a suspension of cells of the same species, is included 

 for comparison to the data obtained with the extracts. 



Among the several points of interest shown by these data are the 

 following: (1) the changes in luminescence intensity after applica- 

 tion of pressure are reversible upon release of pressure, (2) a fairly 

 sudden but transitory increase in intensity ( "spike" ) occurs on sudden 

 application of pressure, and a fairly sudden but transitory decrease 

 ("dip") occurs on sudden release of pressure, (3) the spikes and 

 dips are followed by relatively slow changes to a new steady-state 

 level under increased or at nomial pressure, respectively, (4) the new 

 steady-state level is lower, nearly the same, or higher than the initial 



