Detection of a 10 kDa breakdown product containing the C-terminus of the D1-protein in photoinhibited wheat leaves suggests an acceptor side mechanism.

Photoinhibition of intact leaves of wheat generates a 10 kDa breakdown product which is clearly observed both at 4 degrees C and 25 degrees C. Selective immunoblotting has shown that the 10 kDa fragment contains the C-terminus of the D1-protein and, under the conditions employed, supports an acceptor side mechanism for photoinhibition in vivo. Although a corresponding 23 kDa N-terminal D1-fragment was not detected our results are consistent with the argument that the primary cleavage site is in the loop joining putative transmembrane segments IV and V.