BENTLEY GLASS 849 



Tlie thiixl general type of hiiiiinesceiit system, that ol the himiiious 

 bacteria. iitiH/es a llaviii nioiioniu leotkle as substrate, that is, as 

 "hiciferin"; and it retjiiires, in ackUtion t() moleciihir oxygen, also 

 a long-chain aliphatic aldehyde, which presmnably becomes boinid to 

 the enzyme together with t\\'o molecides ol reduced flavin phospiiate. 

 The function of the aldehyde is not clear, but perhaps through per- 

 oxidation (as McElroy and Green have suggested) it jnovides some 

 of the excitation energy needed in the luminescent reaction. When 

 all essential components of the system are in limiting concentration, 

 the total amoiuit of light emitted is proportional to the amoiuit of 

 aldehyde added, with an efficiency of one quantum per 20 molecules 

 of aldehyde. Aldehydes with an even number of carbon atoms in- 

 crease in efficiency wath increasing chain lengths, but those with an 

 odd number reach a maximiuii effectiveness with nine carbons (Rogers 

 and McElroy) . As in the Cypridina system, a non-luminescent oxi- 

 dation of the flavin can occur in a competing reaction. 



McElroy and Green, who purified the bacterial luciferase and 

 found it to have a molecular weight of about 85,000, showed that two 

 molecules of reduced flavin (FMNHo) are required in the reaction. 

 As a possible mechanism, it is suggested that one FMNHo molecule 

 reacts with oxygen to form a peroxide, while the other FMNHo mole- 

 cule unites with the aldehyde which then, by reaction with the organic 

 peroxide, becomes oxidized to a highly excited state that emits light. 

 But it is also possible that the aldehyde is involved only in dark 

 reactions coupled with the luminous reaction and is not a direct 

 participant in the latter (Strehler) . At present there seems no way 

 of deciding between these possibilities. 



Johnson and his coworkers do not regard either the differences in 

 the fluorescent and chemiluminescent spectra of the varieties of hici- 

 ferin found in different organisms, or the disjunct phylogenetic oc- 

 currence of bioluminescence, or the failure to obtain cross-reactions 

 between different "luciferins" and "luciferases", or the specific re- 

 quirements for different cofactors as sufficient ground for supposing 

 the several bioluminescent systems to be entirely different in chemical 

 nature. Although three main types of bioluminescent systems are dis- 

 tinguishable, they may in the long run turn out to be more similar 

 than different. These workers are strengthened in this view by their 

 recent finding of a luminescent cross-reaction between the luciferin 

 and luciferase of a fish, Apogon, and the crustacean Cypridina. The 

 absorption sjiectra of the respective luciferins are quite similar, but 

 not identical; and there is a reasonable j^resumption that the j)ro- 



