Segmental flexibility of ribosomal protein S1 bound to ribosomes and Q beta-replicase |
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Authors: | Y G Chu C R Cantor I Sawchyn P E Cole |
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Institution: | Department of Chemistry, Columbia University, New York, NY 10027, USA |
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Abstract: | The protonization pattern of the endogenous donor component D1 which feeds electrons directly into chl-a+II has been analyzed in Tris-washed inside-out thylakoids with the aid of appropriate pH-indicators. It was found that under repetitive flash excitation the amount of protons released is proportional to the extent of D1-oxidation, depending on the time between the flashes. The kinetics of D1-oxidation (being practically the same as in normal Tris-washed chloroplasts) are faster than the proton release by two orders of magnitude. The results lead to the conclusion that D1 is protonized in the reduced state with pK(Dox1) < 5 and becomes deprotonized in the oxidized state with pK(Dred1) ? 8. The proton release is kinetically limited by a transport barrier. Implications on the interpretation of the proton release pattern in preparation with intact water oxidation are discussed. |
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Keywords: | QB replicase Protein S1 Ribosome Polarization Fluorescence Anisotropy NEM AEDANS iodoacetylethylenediamine (1 5)-naphthol sulfonate AEDANS-S1 R-S1 Qβ replicase lacking the S1 subunit |
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