Membrane protein damage and repair: removal and replacement of inactivated 32-kilodalton polypeptides in chloroplast membranes.

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Abstract
Incubation of Chlamydomonas reinhardii cells at light levels several times more intense than those at which the cells were grown results in a loss of photosystem II function (termed photinhibition). The loss of activity corresponded to the diasppearance from the chloroplast membranes of a lysine-deficient, herbicide-binding protein of 32,000 daltons which is thought to be the apoprotein of the secondary quinone electron acceptor of photosystem II (the Qb protein). In vivo recovery from the damage only occurred following de novo synthesis (replacement) of the chloroplast-encoded QB protein. The turnover of this protein is a normal consequence of its enzymatic function in vivo and is a physiological process that is necessary to maintain the photosynthetic integrity of the thylakoid membrane. Photoinhibition occurs when the rate of inactivation and subsequent removal exceeds the rate of resynthesis of the QB protein.