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Articles

Chlorophyll-Protein Complexes from Euglena gracilis and Mutants Deficient in Chlorophyll b¹

I. Pigment Composition

Institute for Photobiology of Cells and Organelles, Brandeis University, Waltham, Massachusetts 02254

The use of n-octyl--D-glucopyranoside along with sodium dodecyl sulfate improves the retention of chlorophyll (Chl) by chlorophyll-protein complexes (CPs) prepared from thylakoids of Euglena gracilis Klebs var bacillaris Cori and yields several additional complexes. Thylakoids from wild-type (WT) cells, solubilized in these detergents and subjected to polyacrylamide gel electrophoresis at 0°C, yield the following CPs, in order of relative molecular weight, containing the pigments shown in parentheses with their respective molar ratios where determined: CP Ia (Chl a, diadinoxanthin and -carotene; 100:12:5); CP I (Chl a and -carotene; 100:6-12); CPx (Chl and carotenoids); LHCP₂ (light-harvesting CP oligomer) (Chl a, Chl b, diadinoxanthin and neoxanthin; 12:4:3:1); CPy (Chl a, diadinoxanthin and -carotene; 100:14:8); CPa (Chl a and -carotene; 100:18-25) and LHCP (monomer) (Chl a, Chl b, diadinoxanthin and neoxanthin; 12:6:4:1). The LHCP complexes retain up to 40% of the total Chl and 80% of the Chl b in the thylakoids. CP Ia contains only a trace of Chl b (Chl a/b [mol/mol] = 62). The lower amount of Chl b in Euglena (about 10% of Chl a + b) compared to higher plants (about 30% of Chl a + b) is probably a consequence of the lower Chl b (relative to Chl a) in the LHCPs of Euglena rather than of fewer LHCPs being present. G₁BU, Gr₁BSL, and O₄BSL, mutants of bacillaris low in Chl b (1-2% of Chl a + b), lack the CP Ia, LHCP, and LHCP₂ found in wildtype (WT); G₁ and O₄ also lack CPy. The mutants contain reduced amounts of Chl a (two-thirds of WT in Gr₁ and one-third in G₁ and O₄) and neoxanthin (20-40% of WT) but retain levels of -carotene and diadinoxanthin close to those in cells of WT. The CPs remaining in the mutants have pigment compositions very similar to their counterparts from WT.

³ Abraham and Etta Goodman Professor of Biology.

¹ Supported by grant GM 14595 from the National Institutes of Health.