Circular dichroism (c.d.) was measured for four chlorophyll-protein complexes, resolved from sodium dodecyl sulphate extracts of chloroplasts by electrophoresis in polyacrylamide gel containing Deriphat 160 (disodium N-dodecyl beta-imidopropionate), a zwitterionic detergent. The slowest-band (1) complex was found to be identical with the complex CP1 as found on electrophoresis in the presence of anion detergent, but it was in a much higher yield (30% of the chlorophyll a). In band-2 and -3 protein complexes a c.d. pattern described for the complex CP2 could be recognized. Another c.d. component of a split-exciton type with extrema at 680 (-) and 669 (+)nm, together with evidence of disorganized chlorophyll, was found in band-2, -3 and -4 complexes. When a barley (Hordeum vulgare) mutant lacking chlorophyll b was examined, only bands 1 and 4 were obtained, and the c.d. of the band-4 complex was much less affected by disorganized chlorophyll. C.D. spectra resembling that of this band-4 complex could be generated by subtracting the c.d. of complex CP1 from the c.d. of photochemically active mutant chloroplast fragments, or by subtracting the c.d. of complexes CP1 and CP2 from pea (Pisum sativum) chloroplast fragments. The Deriphat appears to have preserved at least to some extent a new type of chlorophyll a-protein complex.

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