Abstract
Beef heart cytochrome c oxidase has been shown to have a boundary layer of -40 phospholipids (PL's) per heme aa3 complex as determined by the immobilization of spinlabeled lipid probes (1, 2). We have been able to subdivide these boundary layer PL's into two main subclasses based upon their ability to exchange with nonionic detergents, e.g., Triton X-100 (TX), Tween 80 or Tween 20, and to measure the effect of this exchange upon the activity of the resulting PLdepleted complexes (3). Most of the boundary layer PL's are not essential for the full activity of the complex since the molecular activity of cytochrome c oxidase is unaltered after exchange of all but about four of the PL's by the nonionic detergent Tween 80. The remaining tightly bound PL's are entirely diphosphatidylglycerol. These few DPG molecules are essential for full activity because their removal results in decreased activity which can be reconstituted by exogenous DPG but not by exogenous phosphatidylcholine (PC) or phosphatidylethanolamine (PE)(3). This report describes an attempt to define the functional PL specificity of the about four essential high affinity sites on cytochrome c oxidase by measuring the effectiveness of a variety of PL's in restoring the full activity of the enzyme that had 40-60% of these essential DPG's removed by detergent exchange.
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