Aggregation of submitochondrial particles by heparin and its application to the study of carnitine transport

A novel technique for the separation of submitochondrial particles from the external medium, an essential procedure in transport studies, was devised. Very low concentrations of heparin (5-10 μg/ml) aggregate the particles and permit their rapid sedimentation in a micro-centrifuge. The transfer of activated fatty acids into mitochondria for oxidation depends on the exchange of matrix carnitine for external fatty-acylcarnitine. To study the matrix face of the carnitine/acylcarnitine translocase, inverted submitochondrial particles were prepared and loaded with L-[¹⁴C]carnitine. As found in intact mitochondria, the K(m) value for L-carnitine was 8 mM, that for palmitoyl-L-carnitine was two orders of magnitude lower, and 11-trimethylaminoundecanoyl-DL-carnitine was a competitive inhibitor. The properties of the carrier exposed to the outer and to the matrix sides of the mitochondrial inner membrane are thus similar.