A re-examination of some properties of fatty acyl-CoA micelles

Three separate techniques have been employed to estimate the critical micelle concentration: spin labeling using 6-doxylstearoyl-CoA, gel permeation chromatography, and analytical ultracentrifugation. The first method is a labeling technique. The latter two methods utilize no potentially interfering probe and provide a value for the aggregation number for palmitoyl-CoA. All three methods provide a critical micelle concentration for palmitoyl-CoA no lower than 30 to 60 microM. The latter methods provide an aggregation number near 40 and certainly no larger than 200. These values are inconsistent with the values suggested earlier (Zahler, W. L., Barden, R. E., and Cleland, W. W. (1968) Biochim. Biophys. Acta 164, 1-11). The spin-labeled analogues, 6- and 16-doxylstearoyl-CoA, were shown not to micellize, yet these analogues were good inhibitors for citrate synthase. These observations will require the re-examination of a large body of literature in which inhibition of enzymes by fatty acyl-CoA at concentrations below 30 microM was simply ascribed to the formation of micelles.