The M-subunit primary structure of the reaction centre (RC) from ChloroJexus auruntiacus composed of 306 amino acid residues has been determined by parallel analysis of the protein and corresponding DNA. The blocked N-terminus as well as replacement of the essential histidine liganding Mg of an accessory bacteriochlorophyll in purple bacteria by leucine distinguishes the M-subunit of Chloroflexus RC from that of purple bacteria.
The L-subunit primary structure of the reaction centre from Chlorofexus auruntiacus composed of 310 amino acid residues has been determined by parallel analysis of the protein and corresponding DNA. Significant homology between this protein and L-subunits from reaction centres of purple bacteria is observed. This implies close similarity in the tertiary structure of these proteins.
The mutual disposition of the a-helical intramembrane rods in Na+,K+-ATPase subunits was studied by photolabelling of the membrane-bound enzyme with 3-(trifluoromethyl)-3-(m_PZ5I]iodophenyl)diazirine (pzsI]TID). Under the chosen conditions for modification, the ratio of label incorporated into the subunits was found to be a/b= 2.2, demonstrating the peripheral location of the p-subunit in the oligomeric membrane complex. The ~ZSI]TID-labelled p-subunit was subjected to tryptic hydrolysis and the modified fragment (ThIJ7-Arg71) was isolated. The labelled amino acid residues are located predominantly on one side of the helix, which is helpful in unravelling the spatial orientation of the &subunit relative to the a-subunit.
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