Two distinct types of ɛ‐binding site exist in chloroplast coupling factor (CF1)

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Abstract
Isolated chloroplast coupling factor (CF1), when depleted of its ɛ‐subunit, has a high ATPase activity which can be inhibited by binding ɛ to a single high‐affinity (K d = 1.4 × 10−10 M) site. In CF1 reduced by dithiothreitol (DTT), however, ɛ at this binding site is no longer inhibitory. Instead, 3 equivalent, lower affinity (K d = 6 × 10−8 M), inhibitory binding sites for ɛ are observed, whether or not the high‐affinity site contains a bound ɛ‐subunit. Binding of ɛ to the high‐affinity site protects CF1 against trypsin activation, while binding to the low‐affinity site does not, showing that occupation of each class of site has a different effect on CF1 structure. The effects of DTT can be interpreted in terms of a reduction in intersubunit cooperativity in CF1.