132 CHEMISTRY OF CYPRIDINA LUCIFERIN 



quinonoid structure are ruled out, but the amino group appears to 

 be present, and it is possible that the oxidation-reduction change in 

 luciferin involves the NH group. 



Anderson (1936) and Korr (1936) by an indirect method have 

 placed the redox potential of luciferin at about +0.26 at pH 7. The 

 rapid oxidation by f erricyanide has been made use of by Chase ( 1949 ) 

 in estimating that the combining weight of luciferin is between 250 

 and 570, while a similar calculation from combination with cyanide 

 indicated 800 to 2400 (Giese and Chase, 1940). Such calculations are 

 subject to revision, depending on the amount of impurity present. 



Recent methods of purification and approach to the structure of 

 Cypridina luciferin such as infrared spectroscopy, chromatography, 

 and acid hydrolysis have been initiated by Mason ( 1952b) and Mason 

 and Davis (1952). Together with a fourth approach, paper electro- 

 phoresis, they will be discussed subsequently. Infrared spectroscopy, 

 carried out with thin films of dried doubly cycled luciferin, has re- 

 vealed strong absorption bands at 3250, 2825, 1680, 1625, and 1510 

 cm"~^, collectively indicating the amide bond as it occurs in peptides 

 or in cyclic ureides. Acid hydrolysis of paper chromatographed lu- 

 ciferin has yielded a yellow pigment and some eight amino acids, a 

 result which led Mason (1952b) to the designation of Cypridina 

 luciferin as a chromopolypeptide of a cyclic nature. A polypeptide 

 structure of luciferin would place it in the group with a number of 

 naturally occurring biological compounds, particularly the antibiotics 

 gramicidin and polymixin, but with the addition of a color group. 

 The solubilities of Cypridina luciferin are surprisingly similar to the 

 cyclopeptide gramicidin, with the one exception that luciferin is more 

 soluble in water. 



The primary objective of the current work has been to isolate pure 

 Cypridina luciferin and establish a criterion of purity, while the ulti- 

 mate goal is the isolation of luciferin in sufficient quantity to permit 

 the elucidation of the structure by physical and chemical means. Three 

 main lines of investigation have been pursued in an attempt to iso- 

 late pure luciferin: (1) paper chromatography, (2) separation on 

 ion-exchange resins and other adsorbents, and (3) filter paper elec- 

 trophoresis. Spectral absorption measurements and fluorescence ob- 

 servations have been made on the highly purified luciferin, as well 



