292 STUDIES ON BIOLUMINESCENCE. IX 



peroxidases, nor will the peroxidases oxidize luciferin with light pro 

 duction. Dubois' researches show that Pholas luciferase differs in 

 some properties from Cypridina luciferase, and my own work^^ indi- 

 cates that firefly luciferase is more like that of Pholas. A compara- 

 tive study of other species of luminous animals is needed in order to 

 delimit more accurately the class of lucif erases as a whole. 



Luciferin presents many characteristics in common with the pro- 

 teins, but two, which, to say the least, throw doubt on its protein 

 nature: (1) its peculiar solubility (in alcohols, esters, and glacial acetic 

 acid), (2) and its resistance to digestion by proteases, even by trypsin 

 which has almost universal digestive action. These two peculiarities 

 have been discussed above. We can only say that if a protein, lucif- 

 erin must belong to a new group differing from known natural proteins 

 in these respects. In general characteristics this new group would 

 fall somewhere on the border-line between the proteoses and peptones. 

 It would not be surprising to find in nature proteoses or peptones sol- 

 uble in absolute alcohol. We know also that some NH-CO linkages 

 of proteins are broken down with great difficulty by trypsin as it is 

 difficult to obtain a tryptic digest of protein which does not give the 

 biuret reaction, and the work of Fischer and Abderhalden has shown 

 that certain artificial polypeptides are not digested by pure activated 

 pancreatic juice. We have, then, three possibilities. Luciferin is 

 (1) either a natural proteose not attacked by trj^psin, or (2) if attacked 

 by trypsin, its decomposition products (presumably amino-acids) 

 still contain the group oxidizable with light production, or (3) it is 

 not a protein at all. I believe that luciferin has too many protein 

 characteristics to conform to the last possibility. I have been unable 

 to oxidize with light production various mixtures of amino-acids (from • 

 beef and casein) by means of luciferase and consequently am led to 

 believe that luciferin is a new natural proteose, soluble in absolute 

 alcohol and not digested by trypsin. 



Dubois believes Pholas luciferin to be a natural albumin with acid 

 properties. Cypridina luciferin could not possibly be regarded as an 

 albumin, but it is very likely that the luciferins of different species of 

 luminous animals differ in certain characteristics. As in the case of 



15 Harvey, Am. J. Physiol, 1917, xlii, 342. 



