Abstract
1. When irradiated 8-azido-ATP becomes covalently bound (as the nitreno compound) to beef-heart mitochondrial ATPase (F 1) as the triphosphate, either in the absence or presence of Mg 2+, label covalently bound is not hydrolysed. 2. In the presence of Mg 2+ the nitreno-ATP is bound to both the α and β subunits, mainly (63%) to the α subunits. 3. After successive photolabelling of F 1 with 8-azido-ATP (no Mg 2+) and 8-azido-ADP (with Mg 2+) 4 mol label is bound to F 1, 2 mol to the α and 2 mol to the β subunits. 4. When the order of photolabelling is reversed, much less 8-nitreno-ATP is bound to F 1 previously labelled with 8-nitreno-ADP. It is concluded that binding to the α-subunits hinders binding to the β subunits. 5. F 1 that has been photolabelled with up to 4 mol label still contains 2 mol firmly bound adenine nucleotides per mol F 1. 6. It is concluded that at least 6 sites for adenine nucleotides are present in isolated F 1.
Published Version
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