JBC, Vol. 252, Issue 5, 1814-1818, Mar, 1977
Requirement of the delta subunit of chloroplast coupling factor 1 for photophosphorylation
H. M. Younis, G. D. Winget and E. Racker
1. Chloroplast coupling factor (CF1) can be prepared by a rapid and simple
procedure after release of the protein from the membrane by brief exposure
to chloroform. It is suitable for large scale preparation of the coupling
factor. 2. The protein contains five subunits (alpha, beta, gamma, delta,
and epsilon in order of decreasing molecular weight) and serves as a
coupling factor for photophosphorylation. However, when this preparation of
CF1 was passed through a DEAE-Sephadex A-50 column, a protein with four
subunits, missing the delta subunit, was obtained. The four-subunit protein
did not serve as a coupling factor. 3. Photophosphorylation was restored to
CF4-depleted chloroplast by addition of the four-subunit protein together
with a partially purified preparation of the delta subunit. The latter
subunit, when added alone, not only did not stimulate photophosphorylation
but consistently diminished the residual activity. 4. The delta subunit is
required for the binding of CF1 and may represent the stalk seen in
electron micrographs as a link between the protein and the membrane.