610 



LIGHT AND LIFE 



TABLE 1 

 Oxygen Exchange Measured with O"* 



Cofactor 



none 



2 X 10-» M FMN 



2 X 10-5 M FMN 



(plus 8X10-^ M DCMU) 

 1.2 X 10-5 M Ks 

 1.2 X 10-5 MY.:, 



(plus 4 X 10-' M DCMU) 



Aimoles Pi esterified /iatoms oxygen 



Consumed Produced 



All values are per mg chlorophyll per hour. DCMU, dichlorophenyl dimethyl urea. 

 Data of Nakamoto, Krogmann, and Mayne (3). 



oxygen is evolved and reconsumed when FMN or menadione are 

 cof actors. A tridy anaerobic cycling involving neither production nor 

 reconsumption of molecular oxygen can apparently occur also, and 

 is most pronounced with pyocyanine and phenazine methosulfate, less 

 so with K3, and hardly at all with FMN. The evidence for this state- 

 ment is complex. One line of evidence is derived from the inhibitory 

 effects of oxygen observed luider certain circumstances. This aspect 

 of the problem has been discussed by Jagendorf, and we add only 

 the statement that we are in general agreement with his conclusions. 

 Another line of evidence derives from the effect of catalase and ethanol 

 on the photoj)hosphorylation reactions. These reagents serve as a 

 trap for HoO^ (1,2). If FMN or K^ are employed at concentrations 

 which give optimal photophosphorylation rates in an atmosphere of 

 Ho, added catalase and ethanol strongly inhibit the phosphorylation. 

 Some representative data are shown in Table 2. The cofactor con- 

 centrations here employed were sufficient to give optimal "anaerobic" 



TABLE 2 

 Inhibition of "Anaerobic" Phosphorylation by Catalase-Ethanol 



Cofactor 

 2X10-^ M FMN 



1.2 X 10-^ M K3 



Catalase-ethanol 



+ 



Added from side arm 



-APi 



.Assay system contains 100 /xmoles of Tris buffer of/;H 7.8, 10 /umoles MgCM.., ") Mmoies 

 ADl', .') ^iniolcs I',, 0.1 ing chioropliyll, in final vohnnc of 'Z.'> nil. N'csscis flushed with 

 Ha (Pd inset) and prciiluininated for 10 niiniiics prior 10 addition of contents of 

 side-arm. Iik iihalion linic. 1") mimiles; red light; temp ziz l.")°('.. 



