Properties of light-harvesting chlorophyll a/b-protein, and photosystem I chlorophyll a-protein, purified from digitonin extracts of spinach chloroplasts by isoelectrofocusing

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A procedure for purifying both light-harvesting chlorophyll a/b-protein and photo-system I chlorophyll a-protein from digitonin extracts of spinach chloroplasts is described. This procedure uses isoelectrofocusing on Ampholine at the last step and permits isolating all of the chlorophyll-proteins from the same extract in a better yield and a highly pure state. The purified light-harvesting chlorophyll a/b-protein which has an isoelectric point (pI) of 4.35 (±0.1) and a single polypeptide of 24 kilodaltons (kD), shows slightly higher chlorophyll a/b ratio of 1.35 than the values reported for the preparations obtained by anionic detergents. This chlorophyll-protein exhibits a markedly high and sharp fluorescence band at 681 nm at 77゜K which is not found on the chloroplast emission spectrum. Photosystem I chlorophyll a-protein focuses on Ampholine into two bands with pI values of 4.75 (±0.1) and 4.80 (±0.1). These two fractions show the same absorption spectra (maximum at 678 nm at room temperature) and emission spectra (maximum at 734 nm at 77゜K) and have the same constituent polypeptides: one large band at 55-64 kD and six minor bands (21.5, 20, 19, 18, 16 and 15 kD). The polypeptide composition and the P-700 to chlorophyll a ratio (1 to ca. 80) of this preparation are very similar to those of the photosystem I reaction center preparation obtained from Swiss chard chloroplasts by Bengis and Nelson (8) .
日本植物生理学会の論文