/•. H. JOHXSOX, /•:. H.-C. S/E. AND Y. HANEDA 215 



luminescence on the phylogenetic tree could conceivably represent 

 diflerences primarily in the efficiency of light emission, due to dif- 

 ferences in internal cellular environments, such as the presence of 

 cjuenching agents, or absence of a factor such as the aldehyde (e.g., 

 in aldehyde-less nuitants (10) ) of the bacterial system, which is 

 somewhat non-specific in the sense that palmitic aldehyde, effective 

 in promoting light emission of this system, is of some general occur- 

 rence in cells. Finally, the failure to obtain "cross-reactions," or even 

 a luciferase-luciferin reaction, in crude extracts of different organisms 

 could restUt in considerable measure from the presence of inhibitors, 

 or to dilution, as mentioned earlier. Success in demonstrating a 

 luciferin-luciferase reaction in bacterial extracts depended in part 

 on the elimination of inhibitors and on concentrating the reactants 

 (39, 43, 44) ; the same is true with respect to extracts of higher 

 fungi (1) . Demonstrating the effects of ATP, ADP, and AMP on the 

 hmiinescence of Renilla extracts also necessitated purification of the 

 extracts (7) . It is impossible to say just how many other systems, 

 of the many tested with crude extracts (14, 27, 30), will reveal a 

 luciferin-luciferase reaction or a function of ATP in light emission, 

 until suitably purified preparations become available. It is reasonable 

 to expect that new types of organic cofactors, in addition to adenosine 

 phosphates and flavin nucleotides, will be ultimately discovered, and 

 the word "luciferin" will take on a definite meaning, such as the 

 substance or complex that actually emits, in the systems that are 

 still biochemically obscure. 



At the moment three general types of kmiinescent systems, illus- 

 trated by those discussed above, can be recognized, namely, {i) the 

 simple enzyme-substrate system, as in the crustacean Cypridina, the 

 protozoan Gonyaulax (31), and possibly the fungi Collybia and 

 Armillaria (1), even though the last of these three types appears to 

 require DPNH; (//) systems that require in addition to a luciferin 

 and luciferase, one or another of the adenosine phosphates, as in 

 the firefly (35) and the sea pansy Renilla (7) ; and {iii) systems that 

 involve an enzyme plus a flavin and an aldehyde, as in linninous 

 bacteria (39, 43, 44) . The easily auto-oxidizable flavin system needs 

 a continual source of hydrogen transfer from a more reduced com- 

 pound, such as DPNH, for sustained luminescence. The role of 

 DPNH in fungal luminescence is perhaps somewhat analogous. 



Despite differences in detail, the fundamental types of luminescent 

 systems among different types of organisms may ultimately turn out 

 to be relatively few. Suggestive evidence in favor of this view re- 



