602 



I 



Jagendorf and Hind 



Figure 1. Time courses relevant to light induced 

 ATP-ase. 



• • Dark hydrolysis of ATP formed by two 



minutes' illumination of chloroplasts with labeled 

 phosphate (70 mumoles), MgCl2 (l mM) and AD? 



(7,5 mumoles). ^ A Light activation of ATP-ase. 



Chloroplasts illuminated for duration shown with cold 

 phosphate, magnesium and ADP (^,0 mumoles); then 

 immediately incubated with labeled ATP (3.5 mumoles) for 



two minutes in darkness. O O Phosphorylation 



of ADP accompanying light activation. Chloroplasts 

 illuminated for times shown with labeled phosphate, 

 magnesium and ADP (7.5 mumoles); then injected into TCA. 

 Chlorophyll 250 ug. Pyocyanine 50 uM. Volume 1 ml. 

 pH 8.0 and 5°C. 



The ATP breakdown that we see differs from that 

 observed by Avron (5) in that Ca ions added in either 

 the light or the dark stage inhibit the present 

 activity. It differs from the ATPase observed first by 

 Petrack and Lipmann (4,6) in that high concentrations 

 of -SH compounds are not added to accomplish the light 

 activation. It may differ from both of them in greater 

 sensitivity to inhibition by adenylates. Our feeling is 

 that the low ADP concentrations used in these experiments 

 (ca. 5 uM) seems closer to physiological than in the 

 more usual ATPase or photophosphorylation experiments. 



Non-phosphorylated intermediate. The very first 

 experiments using chloroplasts illuminated in a syringe 

 produced the startling discovery that the complete 

 phosphorylation reaction, from added ADP, phosphate and 

 magnesium, could occur in the dark. (This result showed 

 up in a control, included as a gesture in the direction 

 of symmetry and completeness, rather than by forethought). 

 Clearly in the light an intermediate was being formed, 

 having very great lability during the subsequent dark 

 period. Its dark decay proceeded with a half-life of 

 0.5 seconds at pH 8 and room temperature, or about 

 2 seconds at 3°C (2). We have designated this 

 intermediate as X , and define it by the ability to make 

 ATP52 in the darkt from added P^^ ^nd ADP. Very similar 

 results were reported independently by Shen and Shen 

 (8). 



