Abstract
The effect of Mg2+ on the binding of adenylates to isolated chioroplast coupling factor 1 (CF1) was studied using CD spectrometry and ultrafiltration. At adenylate concentrations smaller than 100 μM, one mole of CF1 binds three moles of ATP (or ADP) regardless of the presence of Mg2+. In the presence of Mgt+, the first two ATP's bind to CF1 independently with the same binding constant of 2.5×10-1 μM-1, then the third ATP binds with a much higher affinity of 10 μM-1. In the absence of Mg2+, the first ATP binds to CF, with a binding constant of 2.5×10-1 μM-1, then the other two ATP's bind less easily with the same binding constant of 4.0×10-2 μM-1. The binding mode of ADP to CF1 is quite similar to that of ATP. In the presence of Mg2+, the binding constants of the first two ADP's are both 7.6×10-2 μM-1, that of the third ADP being 4.0 μM-1. In the absence of Mg2+, the binding constant of the first ADP is 7.6×10-2 μM-1, the constants of the other two ADP's both being 4.0×10-2 μm-1. AMP caused a negligible change in CD.
