Antenna protein composition of PS I and PS II in thylakoid sub-domains

• Spinach thylakoids were separated into grana core, grana margin, and two different stromal lamella fractions in the absence of detergents. The levels of all light-harvesting chlorophyll a/b-binding (LHC) proteins were determined in all fractions, and were normalised to the amount of Photosystem I (PS I) and Photosystem II (PS II) centres. PS I beta in the stroma lamellae was found to have a full complement of Lhca polypeptides and, probably, one attached LHC II trimer. PS I alpha binds additional LHC II trimers, but PS I centres located in the inner parts of the grana stack lack Lhca1 and are depleted in Lhca4. PS II beta, found in grana margins and stroma lamellae, seems to associate one monomer each of Lhcb4, Lhcb5 and Lhcb6 (CP29, CP76 and CP24, respectively) and one LHC II trimer consisting of two Lhcb1 and one Lhcb3 subunit. PS II alpha has additional LHC II trimers (consisting of Lhcb1 and Lhcb2) attached. We also find evidence for the existence of both PS I and PS II centres in the extreme stroma (probably centres being synthesised or repaired), that lack all LHC proteins. (C) 1997 Published by Elsevier Science B.V.

Nyckelord

light-harvesting chlorophyll a/b-binding protein I

light-harvesting chlorophyll a/b-binding protein II

grana

grana margin

stroma exposed thylakoid

heterogeneity

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