562 THE BIOLOGY OF MARINE ANIMALS 



in many other forms. This information is summarized in Table 13.2. It is 

 surmised that the reactant substances luciferin and luciferase may be 

 involved in the luminescence of those forms that have given negative 

 results, but have not been revealed by the techniques hitherto employed. 



Photogenic materials show a high degree of specificity, and lumines- 

 cence can be produced only by mixing luciferin and luciferase from the 

 same species or, at most, from closely related forms. Harvey found that 

 light resulted from mixing luciferin and luciferase extracts from two 

 different genera of ostracods, Cypridina and Pyrocypris, but not from 

 combining extracts of Cypridina and the decapod Systellaspis, both Crusta- 

 cea, but belonging to different sub-classes. Neither is light produced by 

 mixing preparations of luciferin and luciferase from members of different 

 phyla. 



Most chemical work has been done on Cypridina extracts, and these 

 have been obtained relatively pure. Luciferin is a non-protein substance of 

 relatively low molecular weight, which is dialysable and is not destroyed 

 by trypsin. It is soluble in water, alcohols and acetone, but not in certain 

 fat solvents (benzene, ether, light petroleum). It can be salted out with 

 ammonium sulphate and is readily adsorbed on fine particles. Recent 

 methods of purification involve extraction with methanol and butanol 

 under hydrogen and two cycles of benzoylation ; paper chromatography 

 and electrophoresis have also been employed. Purified luciferin contains 

 amino-acids and shows some properties of polypeptides (54). 



Luciferase is a non-dialysable substance having some protein character- 

 istics. It is heat-labile and is destroyed by trypsin. It is insoluble in al- 

 cohols and fatty solvents, and dissolves in water, dilute salt, acid and basic 

 solutions. It is salted out with saturated ammonium sulphate and is readily 

 adsorbed on fine particles. Its reactions are those of an albumen; it has 

 the characteristics of an enzyme, and specifically it catalyses the oxidation 

 of luciferin, with energy release in the form of light. 



It now appears that the luciferins from different groups of animals are 

 chemically quite different from each other. Crude luciferin extracts from 

 one group of animals fail to luminesce when added to luciferase extracts 

 from other sources. They differ also in their responses to oxidizing agents 

 and catalysts; dependence on 2 , A.T.P. and accessory factors; and in 

 fluorescence. Independently of such variables, luciferin is defined as an 

 oxidizable substance capable of absorbing enough excess energy from some 

 chemical reaction to emit light in the visible region (13, 28, 29, 37, 

 39). 



The actual amounts of photogenic substances necessary to produce 

 luminescence are sometimes very small. With dried Cypridina preparations 

 one part of luciferin extract will just show light when mixed with luciferase 

 in 4x 10 8 parts of sea water, whereas the threshold for luciferase extract 

 is one part in 8 x 10 7 parts sea water. In Pholas, on the other hand, rela- 

 tively concentrated solutions of luciferin and luciferase are necessary to 

 give visible light on mixture. 



