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Light‐dependent degradation of the Q B ‐protein in isolated pea thylakoids
Author(s) -
Ohad I.,
Kyle D.J.,
Hirschberg J.
Publication year - 1985
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1002/j.1460-2075.1985.tb03833.x
Subject(s) - biology , thylakoid , degradation (telecommunications) , chloroplast , biophysics , biochemistry , gene , telecommunications , computer science
The 32 000‐dalton Q B ‐protein of photosystem II (PS II) is rapidly damaged and removed from isolated pea thylakoids during incubation in the light resulting in a loss of photosynthetic electron flow through PS II. This in vitro photoinhibition is similar to that previously reported with intact Chlamydomonas cells. The damage occurs at a faster rate in vitro , however, due to the inability of isolated thylakoids to synthesize replacement Q B ‐protein. The removal of the damaged Q B ‐protein does not require any soluble components of the chloroplast stroma and is unaffected by the protease inhibitors phenyl‐methylsulfonylfluoride or antipain. Unlike the effect of trypsin, no low mol. wt. membrane‐bound or soluble fragments of the labelled Q B ‐protein could be identified either by autoradiography or immunologically using polyclonal antibodies specific for the Q B ‐protein. The lightinduced damage to the Q B ‐protein (indicated by a loss of Q B functional activity), preceded the removal of the protein from the membrane. We conclude that photodamage of the Q B ‐protein generates a conformational change which renders the protein susceptible to attack by a highly efficient, intrinsic membrane protease.