文摘
The heme-copper cytochrome oxidase of Escherichia coli (cytochrome bo3) was tagged witholigohistidine at the C-terminus of the small noncatalytic subunit IV. After detergent solubilization, theenzyme was purified by a one-step procedure with immobilized metal affinity chromatography. Usingdifferent cytochrome bo3 constructs as reference, the products were investigated by mass spectroscopicaland immunological methods. Several posttranslational modifications of subunits II, III, and IV wereobserved: (1) N-terminal methionines of subunits III and IV are split off. (2) Fifty percent of subunit IIIpolypeptides are acetylated, presumably at the N-terminal alanine. (3) Lipoprotein processing of subunitII involves cleavage of the signal peptide. (4) Maturation of subunit II [Ma, J., Katsonouri, A., and Gennis,R. B. (1997) Biochemistry 36, 11298-11303] alters the structure of the N-terminal cysteine byN-palmitoylation and S-glyceryldipalmitoylation. (5) A hexapeptide is split off from the C-terminus ofsubunit II. This happens subsequently to the N-terminal lipoprotein processing step and is dependent onthe growth state of cells.