Biophysical Journal 6: 353-366 (1966)
© 1966 the Biophysical Society

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Spectral Studies of a Chlorophyll Pigment with Fluorescence Maximum at 698 mµ

ABSTRACT

A chlorophyll type pigment (F698) fluorescing maximally at 698 mµ at 77°K has been observed in preparations of chlorophyll. This fluorescence is quenched by small amounts of naturally occurring materials, including plastoquinone and the ubiquinones, and by nitrobenzene, probably by formation of a nonfluorescent complex. Fluorescence quenching does not occur in the presence of carotenes, xanthophylls, or reduced plastoquinone and ubiquinone. The fluorescence is sharply temperature dependent, with a steep rise in intensity occurring at 165°K. At 77°K the fluorescence yield is between 0.8 and 1.0. The red absorption maximum of the pigment is at 675 mµ at room temperature and at 688 mµ at 77°K. In vivo, a low temperature emission is also observed at 698 mµ, and this fluorescence is quenched by nitrobenzene. It is proposed that the pigment found in vitro is also the one responsible for emission at 698 mµ in vivo. A reaction of F698 with plastoquinone is suggested as the primary photochemical step in system II of photosynthesis.