220 LIGHT AND LIFE 



luminescence systems. Mechanisms are proposed for the light-produc- 

 ing reactions, but must be strongly qualified as being only tentative 

 because of our lack of detailed knowledge of the exact mechanism of 

 the more general case of chemiluminescence. 



Firefly Luminescence 



The factors required for light production in extracts from fireflies 

 have now been prepared in a highly purified crystalline state (2, 7) . 

 The crystallization of firefly luciferase and luciferin has allowed for 

 the first time an extensive quantitative study of the interaction of 

 these substances during the process of light emission. Luciferase, 

 purified by repeated crystallization, is homogeneous as judged by 

 electrophoresis and ultracentrifugation, both run at various pH values. 

 This method of purification, which eliminates the contaminating 

 enzyme pyrophosphatase, is an important factor in the interpretation 

 of the kinetics of the reaction. The isoelectric point of luciferase is 

 between pH 6.2 and 6.3, and the sedimentation constant at 25° C 

 is 5.6, a value consistent with a molecular weight of about 100,000 

 (7) . The properties of purified luciferin will be described later. 

 However, the evidence available suggests that it has the empirical 

 formula Ci3H]2N2S203 and, as the following addendum describes, it is 

 probably a benzthiazole derivative (2) . Additional evidence indi- 

 cates that a carboxyl group of luciferin reacts with adenosine tri- 

 phosphate (ATP) to form luciferyl adenylate and inorganic pyro- 

 phosphate (14, 12) . Magnesium ion is required for this activa- 

 tion step. As indicated in Fig. 1, the luciferase-catalyzed reaction 



E + LH2-AMP 



it 



E + LHg-l-ATP ^ * E-LHgAMP+ PP 



O2 



LIGHT 



E + L 4- ATP ^ ' F-l-AMP-f PP 



n 



E+ L-AMP 

 Fig. 1. Siinimaiy of the reactions concerned with liglit emission in firefly extracts. 

 LHo, hicifcrin; A TP, adenosine triphosphate; IM*. pyrophospliate; K. hiciferase; L, 

 oxyhiciferin; LH.-AMl' and L -AMP, liuileryl and oxyhiciferyl adenylic acid, re- 

 spectively. 



