Comparison of two expression systems using COS7 cells and yeast cells for expression of heart/muscle-type carnitine...

Carnitine palmitoyltransferase 1 (CPT1), catalyzing the transfer of the acyl group from acyl-CoA to carnitine to form acylcarnitine, is located at the outer mitochondrial membrane. Because it is easily inactivated by solubilization, expression systems using living cells are essential for its functional characterization. COS7 cells or yeast cells are often utilized for this purpose; however, the advantages/disadvantages of the use of these cells or the question as to how the CPT1 enzyme expressed by these cells differs are still uncertain. In this study, we characterized the heart/muscle-type isozyme of rat CPT1 (CPT1b) expressed by these two cellular expression systems. The mitochondrial fraction prepared from yeast cells expressing CPT1b showed 25% higher CPT1 activity than that obtained from COS7 cells. However, the expression level of CPT1b in the former was 3.8 times lower than that in the latter; and thus, under the present experimental conditions, the specific activity of CPT1b expressed in yeast cells was estimated to be approximately five times higher than that expressed in COS7 cells. Possible reasons for this difference are discussed.