254 LIGHT AND LIFE 



trum of bacterial light (Achromobacter fischeri) is 495 m;;t. This is 

 considerably removed from the yellow-green fluorescence (530 m/x) 

 of riboflavin or FMN. (2) Kinetic data indicate that two reduced 

 FMN molecules may be required. (3) The data demonstrate that 

 total light emission is dependent on the amount of aldehyde added. 

 The utilization of aldehyde occurs rapidly only under conditions 

 which favor light emission. (4) Thermodynamically at least 58 kilo- 

 calories per mole are required to obtain an excited state which will 

 give the peak emission. Since light quanta at the wavelength of 

 420 niyu, are also observed, the energy requirement must be as high 

 as 68 kcal/mole. (5) Hydrogen peroxide added to the complete 

 enzyme system does not stimulate, nor does catalase inhibit. 



From such considerations McElroy and Green (13) suggested the 

 possibility that a peroxidation of an aldehyde molecule was the source 

 of the excitation energy. They suggested that one reduced FMN 

 moleciUe combined with the aldehyde and that the second FMNH2 

 molecule combined with oxygen to form a peroxide similar to that 

 suggested by Drew for aminophthalic hydrazide. The presumption 

 was that the organic peroxide acted as an oxidant for the aldehyde- 

 FMNHo compound to give a highly excited molecule which woidd 

 emit light. Although this proposal is in keeping with the observed 

 facts, there is no direct chemical evidence to support it. It is pos- 

 sible, as Strehler (25) argues, that the utilization of aldehyde repre- 

 sents dark reactions and that such dark reactions occur only under 

 those conditions which support luminescence. Unfortunately, until 

 one can obtain a system which gives a quantum yield of one, as in 

 the case of the firefly, this hypothesis is difficult if not impossible to 

 eliminate. 



ADDENDUM: The Structure of Firefly Luciferin 



Frank McCapra and Ernil H. White 



The following is a brief indication of the probable constitution of 

 luciferin, as deduced from preliminary investigations. 



Luciferin, C13H10.J2O3N2S2, obtainable from the dried light organ 

 of the firefly, is an optically active crystalline solid, highly fluorescent 

 in solution. Earlier evidence has suggested the presence of a car- 

 boxylic acid grouping and a phenolic hydroxyl group. Tests for 

 basic nitrogen, thioketone, or sulfhydryl groups were all negative. 



