Photoactive Subunits of Protochlorophyll(ide) Holochrome.

A stable, soluble, and photoactive protochlorophyll(ide) complex has been extracted from dark-grown barley (Hordeum vulgare L.) leaves with buffer containing saponin and glycerol. After ammonium sulfate precipitation, the redissolved pigment complex was partially purified by chromatography on Sephadex gels in the presence of saponin. With the assumptions that the pigment complex from barley has the same shape and density as the proteins used for calibration, its molecular weight is 63,000. Photoactive protochlorophyll(ide) complex isolated from bean (Phaseolus vulgaris L.) and chromatographed by the same procedures has an aparent molecular weight of 100,000 or greater. No chromatographic separation of photoactive and inactive protochlorophyll(ide) complexes was observed. Photoconversion of protochlorophyll(ide) to chlorophyll(ide) did not change the chromatographic behavior of the pigment complex.The protochlorophyll(ide) complex had an absorption maximum at 644 nanometers and a corresponding fluorescence emission maximum at 652 nanometers. Photoconversion yielded chlorophyll(ide) complex with an absorption maximum at 678 nanometers and a main fluorescence emission maximum at 685 nanometers. Spectrofluorometry on partially photoconverted preparations gave no indication of energy transfer from protochlorophyll(ide) to chlorophyll(ide). This result is consistent with the presence of a single protochlorophyll(ide) molecule per active unit of the pigment complex.It is concluded that the protochlorophyll(ide) complex obtained from barley represents an active subunit of protochlorophyll holochrome.