Abstract
Pseudomonas cytochrome oxidase (EC 1.9.3.2) is composed of two subunits. Each subunit has a molecular weight of approx. 63 000 and, according to the iron determination, contains two hemes. Cytochrome oxidase was subjected to various dissociation procedures to determine the stability of the dimeric structure. Progressive succinylation of 14 to 68% of the lysine residues of the enzyme increases the amount of the protein appearing in the subunit form ( s 20,w ≈ 4 S) from 18 to 92%. At a high degree of succinylation a component with a sedimentation coefficient of approx. 2 S appears. The subunits with sedimentation coefficients of approx. 4 S and 2 S are also formed when the pH is below 4 or above 11. The same molecular weight (63 000) was found for these two components in sodium dodecylsulphate electrophoresis. No dissociation of cytochrome oxidase was observed in salt solutions like 3 M NaCl and 1 M Na 2SO 4, or in 6 M urea. The slight decrease in the sedimentation coefficients in NaCl solutions is partly explained by preferential hydratation of the protein.
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