n. /;. Mcelroy and h. h. seliger 247 



with a trapping center in a crystal lattice or possibly with a wave- 

 length shilier in an organic liquid scintillator. 



As the pH oi the firelly solution is reduced toward acid it can 

 be observed that the yellow-green light intensity decreases tremend- 

 ously, leaving a didl brick orange glow that can be seen in a darkened 

 room. This variation in bioluminescence emission with pH is shown 

 in Fig. 25 for three different pH values. As can be seen, at neutral 

 (and alkaline) pH there is a single emission band in the yellow- 

 green region. At intermediate pH a red emission band appears at 



500 550 600 650 700 



Fig. 27. Emission spectra of fiiefly bioluminescence at neutral pH with and 

 without phosphate buffer. Tlie effect of phosphate ion is similar to a lowering 

 of the })H by approximately 1 unit. 



616 m^ and at pH values below 5.5 ni/x the yellow-green emission is 

 completely suppressed, and only the red band is evident. The quan- 

 tum yield has also been measured for various pH values (Fig 26) . 

 At acid pH the number of light quanta emitted per luciferin mole- 

 cule oxidized is markedly lower than 1, and indicates a predominantly 

 dark reaction. However, at alkaline pH, although the rate of light 

 emission is reduced to a small fraction of the rate at pU. 7.6, the 

 quantum yield is essentially unity. The change of quantum yield 

 with pH corresponds rather closely in form to the fluorescence yield 

 of luciferin and oxyluciferin at various pH's, as shown in Fig. 21, 

 except for the fact that the pKa has been essentially shifted one whole 

 pH unit to the acid range for the bioluminescence quantum yield. 

 This may represent the interaction of the enzyme with the phenolic 



