CORE ANTENNA COMPLEXES, CP43 AND CP47, OF HIGHER-PLANT PHOTOSYSTEM-II- SPECTRAL PROPERTIES, PIGMENT STOICHIOMETRY, AND AMINO-ACID-COMPOSITION

The core antenna complexes of photosystem II, CP43 and CP47, were puri fied from two higher plants by anion-exchange chromatography, using a combination of the chaotropic agent LiClO4 and the nonionic detergent beta-dodecyl maltoside. The Q(y) transition was resolved at 48 K into two main bands near 682.3 and 671.5 nm for CP43, while the CP47 spectr um showed a more complex structure with main bands at 688, 681.2, 676, 670, 667, and 661 nm. Emission bands (77 K) were detected at 683 and 695 nm for CP43 and CP47, respectively. Fluorescence excitation spectr a showed high efficiency of energy transfer between the different tran sitions of the chlorophylls and a somewhat lower efficiency from beta- carotene. The circular dichroism spectrum of CP47 indicated the presen ce of excitonic interactions between some chlorophylls. In contrast, C P43 showed a single negative circular dichroism band at 670 nm. The pi gment content of the complexes was determined by both spectroscopic me asurements and HPLC. Contents of 18 chlorophylls a and 5 beta-carotene s per CP43 polypeptide and 19 chlorophylls a and 3 beta-carotenes per CP47 polypeptide were found, using the methods of Lowry or Bradford fo r protein quantitation. When the protein concentration was determined from the amino acid analysis, 20 chlorophylls a and 5 beta-carotenes p er CP43 and 21-22 chlorophylls a and 4 beta-carotenes per CP47 were ob tained. Thus, a content of 46-48 chlorophylls a was obtained for the c ore complex, assuming 4-6 chlorophylls per reaction center, in agreeme nt with the composition obtained experimentally using a highly purifie d oxygen-evolving core complex. This suggested that no pigments were l ost during the purification procedure. Moreover, the amino acid analys is of the purified complexes revealed a high homology with the amino a cid composition derived from the gene sequences reported for other hig her plants.