Photolabelling with 8-azido-adenine nucleotides of adenine nucleotide-binding sites in isolated spinach chloroplast ATPase (CF 1)

Abstract

1. 1. Photolabelling of chloroplast ATPase (CF 1) with either 8-azido-ATP or 8-azido-ADP leads to inactivation of the ATPase activity. ATP and ADP protect against the inactivation, whereas AMP does not. 2. 2. Ca 2+ has little if any effect on the degree of inactivation by photolabelling with 8-azido-ADP, but, at the same degree of inactivation, twice as much label is bound in the presence of Ca 2+ as in its absence. 3. 3. The degree of inactivation of ATPase and the amount of bound photolabel are independent of the extent of pre-activation of the CF 1. 4. 4. Upon extrapolation to complete inactivation, 2 mol label, either 8-azido-ATP or 8-azido-ADP, are bound per mol enzyme. In the presence of Ca 2+, 4 mol 8-azido-ADP can be bound. 5. 5. In all cases the label is bound specifically to the α and β subunits in almost equal amounts. The location of the bound label is not affected by addition of Ca 2+, ATP or ADP.