Properties of a Purified Carnitine Palmitoyltransferase, and Evidence for the Existence of Other Carnitine Acyltransferases

Abstract

Carnitine palmitoyltransferase (CPT) has been purified, and some of its properties are described. The purified preparations had specific activities of 10–38 μmoles/min/mg protein at 35°. The apparent molecular weight of CPT was approximately 75 000, or a multiple thereof. The K′m value for palmitoyl-CoA was 1.8 × 10−5 M, while the K′s values for (–)-carnitine, CoA–SH, and (–)-palmitoylcarnitine were estimated to be 4.5 × 10−4 M, 5.5 × 10−6 M, and 1.4 × 10−4 M, respectively. The enzyme was subject to inhibition by all substrates and products. CPT had a relatively broad fatty acyl chain-length specificity, with highest Vmax values obtained for the transfer of myristoyl and palmitoyl groups. K′m values were lowest with long-chain fatty acylcarnitinè derivatives (1.9 × 10−4 M for (–)-stearoylcarnitine versus 1.2 × 10−3 M for (–)-decanoylcarnitine).Evidence is presented demonstrating the existence of two additional protein fractions possessing carnitine acyltransferase activities with different fatty acyl chain-length specificities. One, which displayed highest relative activity towards the transfer of octanoyl groups, is tentatively designated carnitine octanoyltransferase. The other, which displayed a high specificity toward the transfer of palmitoyl and stearoyl groups from acylcarnitine when preincubated with CoA–SH, is tentatively designated carnitine palmitoyltransferase II.