Identification of a novel light-harvesting complex II protein (LHC IIc')

The caroteno-chlorophyll-protein, LHC IIc, is a relatively minor component of the PS II antenna. Isolated LHC IIc contains a major protein of 28 kDa along with a 26 kDa subunit in lower abundance. Previously, it was not known if the 26 kDa protein was closely related to the 28 kDa LHC IIc protein or if it was a comigrating LHC IIb contaminating subunit. A sequence of 20 amino acid residues was obtained by direct protein micro-sequencing of an internal cyanogen bromide-derived peptide fragment of the 26 kDa protein isolated from barley. The sequence shows, and antibody reactions confirm, that the 26 kDa protein is similar but distinct from both the 28 kDa LHC IIc and LHC IIb protein sequences, indicating that there remains at least one more cab gene to be identified in higher plants. Furthermore, it is difficult to interpret the data in any way other than that there is a novel LHC II pigment-protein (LHC IIc') that co-migrates with LHC IIc.