Fractionation of Chlorophyll Forms from Euglena and Measurement of Light-Induced Absorbance Changes

Abstract

Aqueous cell extracts of Euglena gracilis containing chlorophyll-a lipoprotein particles with absorption maxima at 670, 680, and 695 m[mu] w were centrifuged immediately following the addition of sodium deoxy-cholate, 5 mg/mg chlorophyll. A fraction sedimenting at 35,000 X g contained all of the chlorophyll a-695 (Ca695) and was enriched in Ca680 and chlorophyll b. The supernatant particles had most of the Ca670 and were enriched in an unidentified carotenoid pigment. In an attempt to correlate the chlorophyll forms with specific steps in photosynthesis, the 2 centrifugal fractions were compared with respect to photoinduced absorbance changes at 591, 518, and 419 m[mu]. Both fractions exhibited slow, reversible increases in absorbance at these 3 wavelenths when irradiated with intense red light ([lambda] > 630 m[mu]). Only the sediment responded to far-red light ([lambda] > 670 m[mu]). The supernatant failed to do so probably because of low absorption by Ca670 beyond 700 m[mu]. Following the addition of electron donors and acceptors, red light induced rapid, reversible increases in absorbance at 518 mu in both fractions, but only the supernatant showed a rapid 591 change which indicated oxidation of plastocyanin. The rapid change at 419 mu associated with cytochrome f was not observed in either fraction. The results suggest that different parts of the electron transport system of photosynthesis are attached to the different pigment complexes.