Two distinct types of ε-binding site exist in chloroplast coupling factor (CF1)

Isolated chloroplast coupling factor (CF sub(1)), when depleted of its epsilon -subunit, has a high ATPase activity which can be inhibited by binding epsilon to a single high-affinity (K sub(d) = 1.4 x 10 super(-10) M) site. In CF sub(1) reduced by dithiothreitol (DTT), however, epsilon at this binding site is no longer inhibitory. Instead, 3 equivalent, lower affinity (K sub(d) = 6 x 10 super(-8) M), inhibitory binding sites for epsilon are observed, whether or not the high-affinity site contains a bound epsilon -subunit. Binding of epsilon to the high-affinity site protects CF sub(1) 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 CF sub(1) structure. The effects of DTT can be interpreted in terms of a reduction in intersubunit cooperativity in CF sub(1).