| Abstract: | The proteolipid subunit of the ATPase complex was identified in whole membranes of the thermophilic bacterium PS-3 by means of a covalent modification with the 14C-labelled inhibitor dicyclohexylcarbodiimide. The proteolipid could be purified from the membrane in free and carbodiimide-modified form by extraction with chloroform/methanol and subsequent carboxymethylcellulose chromatography in mixtures of chloroform/methanol/water. The complete amino acid sequence of the 72-residue polypeptide could be determined by automated solid-phase Edman degradation of the whole protein, and of fragments obtained after cleavage with cyanogen bromide and N-bromosuccinimide. Chemical cleavages and separations of the resulting fragments by gel chromatography were performed in 80% formic acid. The amino acid sequence shows a concentration of hydrophobic amino acids in two segments of about 25 residues at the amino-terminal and carboxy-terminal ends. The polar residues are clustered in the middle of the polypeptide chain. The bound 14C]dicyclohexylcarbodiimide label is recovered exclusively at position 56, which is occupied by a glutamyl residue. The proteolipid from PS-3 exhibits homology to the corresponding ATPase subunit from mitochondria. The carbodiimide-reactive glutamyl residue occurs at the position as in the mitochondrial proteins. |
