The Journal of Cell Biology, Vol 100, 1139-1147, Copyright © 1985 by The Rockefeller University Press
Crystallization of the light-harvesting chlorophyll a/b complex within thylakoid membranes
MK Lyon and KR Miller
We have found that treatment of the photosynthetic membranes of green
plants, or thylakoids, with the nonionic detergent Triton X-114 at a 10:1
ratio has three effects: (a) photosystem I and coupling factor are
solubilized, so that the membranes retain only photosystem II (PS II) and
its associated light-harvesting apparatus (LHC-II); (b) LHC-II is
crystallized, and so is removed from its normal association with PS II; and
(c) LHC-II crystallization causes a characteristic red shift in the 77
degrees K fluorescence from LHC-II. Treatment of thylakoids with the same
detergent at a 20:1 ratio results in an equivalent loss of photosystem I
and coupling factor, with LHC-II and PS II being retained by the membranes.
However, no LHC-II crystals are formed, nor is there a shift in
fluorescence. Thus, isolation of a membrane protein is not required for its
crystallization, but the conditions of detergent treatment are critical.
Membranes with crystallized LHC-II retain tetrameric particles on their
surface but have no recognizable stromal fracture face. We have proposed a
model to explain these results: LHC- II is normally found within the
stromal half of the membrane bilayer and is reoriented during the
crystallization process. This reorientation causes the specific
fluorescence changes associated with crystallization. Tetrameric particles,
which are not changed in any way by the crystallization process, do not
consist of LHC-II complexes. PS II appears to be the only other major
complex retained by these membranes, which suggests that the tetramers
consist of PS II.
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