Solubility of palmitoyl-coenzyme A in acyltransferase assay buffers containing magnesium ions.

The solubility of palmitoyl-CoA is strongly affected by Mg2+ concentrations commonly used in acyltransferase reactions. In 0.10 M Tris-HCl buffer at pH 7.4 or 8.5, all of the palmitoyl-CoA in 10 microM solutions and 90% of the palmitoyl-CoA in 100 microM solutions are precipitated by 1 mM Mg2+. In 0.05 M phosphate at pH 7.4, and in 0.10 M Tris-HCl containing 0.4 M KCl, the substrate remains soluble at Mg2+ concentrations below 4-5 mM. Above 5 mM Mg2+, palmitoyl-CoA is insoluble in all of these buffers. Substrate solubility could therefore be a limiting factor when free Mg2+ and fatty acyl-CoAs are present together during acyltransferase assays.