/?. /.. STREHLER AND I). I). HENDLEY 



605 



iiulicatctl by a (Dinplcic absence ol luminescence prior to the first 

 illumination. 



(b) Effects of myokinase. That the rapid decay in the dark period 

 following illumination is largely due to the myokinase contained in 

 crude firefly enzyme (15) is shown by the results depicted in Fig. 4. 

 In this experiment excess myokinase was added at the indicated time. 

 Note that the rate of increase of luminescence is much depressed in 

 succeeding periods of illumination. Moreover the decay in the sub- 

 sequent dark period is also depressed or absent. 



(c) Effect of cofactors. Fig. 5 illustrates the effect of TPN on the 

 rate of phosphorylation by chloroplasts. The following factors were 

 also effective: TPNH, folic acid, cytochrome c, ferricyanide, PMS, 

 and FMN (4, 5, 8, 12) . 



(d) Destruction of ATP by light. One of the objectives of these 

 experiments was to determine whether illumination will cause utiliza- 

 tion of ATP under conditions where reductive dephosphorylation 

 (21) might have been expected to occur, as postulated by Kandler 

 in 1950 (13) and by Strehler in 1952 (23). Although under most 

 conditions illiunination caused an increase in ATP level as measured 

 by luminescence, A\e have occasionally noticed a decrease in lumines- 

 cence on exposure to light under as yet undefined conditions. Such 



EFFECT OF LIGHT BEFORE AND AFTER ADDITION OF MYOKINASE 



(A 



m 



a: 

 < 



UJ 



u 



z 



UJ 



o 



3 

 _l 



100 - 



80 - 



60 



40 - 



20 



1 2 3 4 5 6 



TIME (Minutes) 

 Fig. 4. Effect of addition of myokinase on luminescence during and 



after illumination. 

 Conditions as in Fig. 2, except that 0.1 ml myokinase was added at 4.5 min. First 

 illumination with 0.3 O.D.U. filter in actinic beam. L, light on. D, light oft. 



