Light-harvesting chlorophyll a/b-binding protein stably inserts into etioplast membranes supplemented with Zn-pheophytin a/b.
Light-harvesting chlorophyll a/b-binding protein, LHCP, or its precursor, pLHCP, cannot be stably inserted into barley etioplast membranes in vitro. However, when these etioplast membranes are supplemented with the chlorophyll analogs Zn-pheophytin a/b, synthesized in situ from Zn-pheophorbide a/b and digeranyl pyrophosphate, pLHCP is inserted into a protease-resistant state. This proves that chlorophyll is the only component lacking in etioplast membranes that is necessary for stable LHCP insertion. Synthesis of Zn-pheophytin b alone promotes insertion of LHCP in vitro into a protease-resistant state, whereas synthesis of Zn-pheophytin a alone does not. Insertion of pLHCP into etioplast membranes can also be stimulated by adding chlorophyll a and chlorophyll b to the membranes, albeit at a significantly lower efficiency as compared with Zn-pheophytin a/b synthesized in situ. When pLHCP is inserted into chlorophyll- or Zn-pheophytin-supplemented etioplast membranes and then assayed with protease, only the protease digestion product indicative of the monomeric major light-harvesting chlorophyll a/b complex (LHCII) is found but not the one indicating trimeric complexes. In this respect, chlorophyll- or Zn-pheophytin-supplemented etioplast membranes resemble thylakoid membranes at an early greening stage: pLHCP inserted into plastid membranes from greening barley is assembled into trimeric LHCII only after more than 1 h of greening.
Kuttkat
A
A
Botanisches Institut, Universität München, Menzinger Strasse 67, D-80638 München, Germany.
Edhofer
I
I
Eichacker
L A
LA
Paulsen
H
H
D002734:Chlorophyll / Q000096:biosynthesis; D000077194:Chlorophyll A; D045342:Light-Harvesting Protein Complexes; D010674:Pheophytins / Q000502:physiology*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D010944:Plants / Q000378:metabolism*; D015032:Zinc / Q000502:physiology*
D045342:Light-Harvesting Protein Complexes; D010674:Pheophytins; D045322:Photosynthetic Reaction Center Complex Proteins; D002734:Chlorophyll; C037184:chlorophyll b; C061694:pheophytin a; D015032:Zinc; D000077194:Chlorophyll A