B. L. STREHLER AND 1). 1). HENDLEY (H)7 



a (iiuling is consisteiii with ihc hypothesis set forth. One such experi- 

 ment is ilhistratctl in Fis^. (i. 1 he recent finding by Petrack (24) ol 

 a liglit-clependent ATPase activity in chlorophists in the presence ol 

 high levels ot suHhydryl compounds is consistent with the above re- 

 sults and intcrjnetation. 



Discussion 



The above findings clearly demonstrate the applicability of the fire- 

 fly luminescence assay to the instantaneous and continuous measure- 

 ment of photosynthetic phosphorylation. Disadvantages of the method 

 for certain applications include the facts that ADP will produce a 

 high backgroiuid luminescence due to myokinase action, that the 

 rapid decay in the dark in the absence of adequate myokinase dis- 

 torts the kinetics of the reaction, and that the decay of luminescence, 

 either because of the flash phenomenon described earlier (17, 18) 

 or the slow deterioration of the enzyme by denaturation or product 

 inhibition (20) , may contribute in some unknown manner to the 

 kinetics. It was possible rapidly to confirm many of the original ob- 

 servations of Arnon et al. and of Jagendorf and his collaborators 

 on the interaction of cofactors and Hill oxidants with the phosphory- 

 lating system. In addition, the early kinetics of the reaction, the 

 absence of appreciable lag under the conditions used, and the ap- 

 parent efficiency of AMP as an acceptor molecule were demonstrated. 

 The absence of induction periods may be due to the myokinase ac- 

 tivity of the firefly enzyme, although the complete absence of lumines- 

 cence prior to illumination and the rapid response cast some doubt on 

 this explanation. In other experiments (11) we have shown that small 

 amounts of ATP facilitate the incorporation of Pj^^-label into added 

 AMP in the light. Nevertheless, it seems possible that AMP itself 

 is an efficient direct acceptor under the present conditions. 



The stimulation of phosphorylation by folic acid may have little 

 direct bearing on the normal mechanism, although the presence of 

 this factor in photosynthetic tissues is suggestive of a more direct 

 function. The mode of its action in vivo, if any, must await further 

 study. 



The negative finding with thioctic acid and thioctamide does not 

 support the proposal of Calvin (27) that closely related cyclic dithiols 

 participate in the early photochemical process. 



Whether or not the decrease in ATP content during illumination, 

 as reported here, supports the theory set forth in 1952 on the basis 

 of intact cell studies (21) must await a further study of conditions 



