title: Protein-protein interactions of the light-harvesting chlorophyll a/b protein. II. Evidence for two stages of cation independent association.
abstract: In a previous paper, we observed a two-stage cation-independent association of the light-harvesting chlorophyll a/b protein from spinach chloroplasts based on concentration-dependent changes in the sedimentation coefficient. The two stages of association occurred between (2-4) and (4-7) mug/ml chlorophyll. In this paper, we provide further evidence for this association. This includes: (1) A decrease in the number of divalent cation binding sites in the second stage of association. (2) A corresponding decrease in the extent of the cation-dependent association. (3) A positive deviation from Beer's law for chlorophyll b for both stages of the cation-independent association and a positive deviation for chlorophyll a for the second stage of association only. (4) A change in the fluorescence emission of both chlorophyll a and b. The change for chlorophyll b was observed for both steps of association whereas that for chlorophyll a was observed for the second step of association only. Therefore, the first stage of association affects only chlorophyll b whereas the second stage alters the environment of both chlorophyll a and b. (5) In addition, divalent cations quenched chlorophyll fluorescence. However, the quenching which required 200-300 muM divalent cation for half-maximal effects was related neither to divalent cation binding nor to the divalent cation-induced association of the protein.
mesh_terms: D000332:Aerobiosis; D000693:Anaerobiosis; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D007700:Kinetics; D008027:Light; D008274:Magnesium; D010940:Plant Proteins / Q000378:metabolism; D010944:Plants; D011485:Protein Binding; D013050:Spectrometry, Fluorescence; D014461:Ultracentrifugation
chemical_list: D010940:Plant Proteins; D002734:Chlorophyll; D008274:Magnesium; D002118:Calcium