Elucidation of the Molecular Properties of Chlorophyll a' and Its Function in Photosynthetic Reaction Centers

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1. Chlorophyll a', in sharp contrast to the ordinary chlorophyll a, forms aggregates with its dimer as the building block, in aqueous alkohols and surfactant aqueous solutions. In view of the long-standing hypothesis that the PSI reaction center, P700, consists of a dimeric chlorophyll, this finding supports an idea that chlorophyll a' constitutes P700 itself.2. By use of barley and cucumber as samples, an HPLC condition has been established that can separate and identify a number of biosynthetic intermediates of chlorophyllous pigments, even for the very early phase of greening of etiolated leaves where only a miniscule amount of chlorophylls are being biosynthesized.3. The greening process of etiolated barley and cucumber has been closely examined with the above-established chromatographic technique. As a result, the relative amount of chlorophyll a' has been found to increase abruptly, in ca. 1 h after the start of greening, to a level more than twice that in mature leaves : this indicates that chlorophyll a' is indeed biosynthesized as an ingredient of the photosynthetic core pigment-protein complexes. Simultaneous examination of the amount of P700 in the course of greening yielded a stoichiometry of chlorophyll a'/P700=2 except for a very early phase, supporting the idea that this minor pigment is functioning in close association with P700.