I). 1). HENDLEY AND B. L. STREHLER 



597 



,32 



Pi'"' INCORPORATION VS. ATP, TPN CONCENTRATION 



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MOLARITY (X 10^) 



Fig. 2. Pi'= incorporation vs. ATP, TPN concentration. Expt. 1: [TPN] varied 

 as shown. Each tube also contained, in Atmoles: K0HPO4, 1.18; ATP, 0.2; MgCL, 

 2.3(i; NaCl, 11.9; tris-HCl buffer pH 8.0, 13.3; 0.1 ml chloroplast suspension. P,»-, 

 1.63 X 10= counts/min. Vol. = 1.13 ml. Expt. 2; [ATP] varied as shown. Each 

 tube also contained TPN, 1.0 /xmoles (•, A) or PMS, 0.05 yumoles (■); salts, buffer, 

 and P,'- as in expt. 1. 116 ^g chlorophyll. Vol. = 1.11 ml. (A- ■): % of ATP 

 labeled, assuming single labeling. In both experiments left-hand ordinate represents 

 total counts/min absorable on charcoal after 20 min incubation at 15°C. 



berates a component capable of being phosphorylated by a succeeding 

 light period under appropriate conditions. In other experiments not 

 tabulated, it was shown that the pre.sence of ATP during the dark 

 incubation was necessary for the stimulation of I'p incorporation in 

 a succeeding light period. 



Fig. 4 shows the effect of dark preincubation on the kinetics of in- 

 corporation of Pi32 in the light. After 20 minutes of dark incubation, 

 5 minutes of illumination results in as much Pj^s incorporation as does 

 20 minutes of illumination without a preceding dark period. 



It would appear from the foregoing data that photophosphoryla- 

 tion of acceptor formed from ATP in the dark explains most of the 



