130 CHEMISTRY OF CYPRIDINA LUCIFERIN 



references to the literature will be found in the book of Harvey 

 (1952). Recently the effect of hydrostatic pressure has been studied 

 quantitatively by Bronk, Harvey, and Johnson (1952); the relation 

 of oxygen concentration to Hght intensity by Hastings (1952). 



Since Anderson's studies, a number of workers have published cer- 

 tain statements concerning the chemistry of luciferin, not all of which 

 have been confirmed by later investigations. The earlier experiments 

 have been reviewed by Harvey (1940) and later findings by Chase 

 (1948), whose work has been especially concerned with the absorp- 

 tion spectrum, to be considered in a later section. It is not yet possible 

 to specify the exact chemical structure of Cypridina luciferin. Early 

 statements have little meaning since they were based not only on 

 very impure material but also on reasoning from one luminous animal 

 to another. It now seems certain that the luciferin of Cypridina is 

 quite different from that of the firefly and from that of luminous bac- 

 teria; a considerable number of luminescent systems have probably 

 arisen independently in evolution ( Harvey, 1953 ) . 



Historically it is interesting to note that at various times Dubois 

 regarded Pholas luciferin as a proteose, a nucleoprotein, or an albu- 

 min with acid properties. Cypridina luciferin has been called a 

 peptone (Harvey, 1919), a phospholipid (Kanda, 1930), a polyhydroxy- 

 benzene derivative (Anderson, 1936; Korr, 1936), a hydroquinone- 

 like compound with a ketohydroxy side chain (Chakravorty and Bal- 

 lentine, 1941), a flavoprotein and pyridine nucleotide (Johnson and 

 Eyring, 1944), and a chromopolypeptide (Mason, 1952b). 



The hydroquinone type of structure was championed by the Dutch 

 group of investigators (Kluyver, van der Kerk, and van der Burg, 

 1942; van der Kerk, 1942), particularly for bacterial luciferin, in the 

 form of l,4-dihydroxynaphthyl-2-hydroxymethylketone. It seems quite 

 certain that this compound cannot be Cypridiiw luciferin, since no 

 light appears when it is mixed with luciferase (Johnson, Rexford, 

 and Harvey, 1949; Spruit, 1949), although related naphthohydroqui- 

 nones have not been ruled out. 



On the other hand, a number of investigators have suggested that 

 flavins are important in bacterial luminescence. It has recently been 

 found that luminescence results when reduced riboflavin or reduced 

 riboflavin phosphate is added to cell-free extracts of luminous bac- 



