Abstract
The stroma lamellar fraction (50000 × g supernatant) obtained by differential centrifugation from French press-disrupted chloroplasts after phosphorylation, found to be enriched in LHC II components, can be separated into an upper, LHC II-poor, and a lower, LHC II-rich, thylakoid membrane zone, by sucrose density gradient ultracentrifugation after Mg 2+ addition. The LHC II-rich zone contains cyt f and peripherally bound CF1 in amount lower than the upper zone, 33 kDa PSII polypeptide in amount higher than the upper zone, and CP I in amount higher than grana membranes. The LHC II-poor zone exhibits more or less the characteristics of stroma lamellae obtained from non-phosphorylated chloroplasts. French-press disruption of isolated grana, incubated in the resuspension buffer used for phosphorylation, releases a ‘light’ thylakoid membrane fraction, rich in LHC II, which behaves on gradient ultracentrifugation like the LHC II-rich fragments separated from phosphorylated stroma lamellae. The results suggest that the enrichment in LHC II components of stroma lamellar fractions, obtained by differential centrifugation of French press or digitonin disrupted chloroplasts, observed after thylakoid protein phosphorylation, reflects contamination of the stroma lamellar fraction by destacked granal membranes.
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