Identification of the photosystem I antenna polypeptides in barley

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Abstract
The light‐harvesting antenna of barley photosystem I (LHCI) was isolated from native photosystem I (PSI) complexes and fractionated into three pigment‐protein subcomplexes using two consecutive rounds of green gel electrophoresis. Each complex showed a characteristic polypeptide composition and low‐temperature fluorescence emission spectrum; they were designated as LHCI‐730, LHCI‐680A and LHCI‐680B. Their four apoproteins of 21, 22, 23 and 25 kDa were purified and NH2‐terminal sequences were determined; in the case of the NH2‐terminally blocked 25‐kDa protein, an internal sequence was obtained after cleavage with endoproteinase Lys‐C. This made possible an assignment of the four proteins to the four types (I–IV) of genes coding for chlorophyll a/b proteins of PSI (cab or lha genes). The LHCI‐730 complex was isolated as a heterodimer composed of the 21‐kDa (LHCI type IV) and the 22‐kDa (LHCI type I) polypeptides. Each LHCI‐680 complex had a single apoprotein. LHCI‐680A consisted of the 25‐kDa (LHCI type III) and LHCI‐680B of the 23‐kDa (LHCI type II) polypeptides. LHCI‐680B was associated with the non‐pigmented PSI‐E subunit, indicating that this protein may function in the binding of this antenna to the reaction centre.