The relationship of rat liver overt carnitine palmitoyltransferase to the mitochondrial malonyl-CoA binding entity and to the latent palmitoyltransferase.

1. Confirming previous work [Murthy & Pande (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 378-382], malonyl-CoA-inhibitable carnitine palmitoyltransferase (CPT1) from rat liver was found to be localized in outer rather than in inner mitochondrial membranes. 2. Antisera were raised against a liver mitochondrial CPT of Mr 68,000, which was presumed to be the latent from of the enzyme (CPT2). These antisera cross-reacted with solubilized CPT extracted from liver inner mitochondrial membranes and with polypeptides of Mr 68,000 and 60,000 in immunoblots of both inner and outer mitochondrial membranes. The antisera also precipitated CPT activity from detergent-treated total membrane and outer-membrane preparations. 3. The antisera did not precipitate [14C]malonyl-CoA binding material obtained either from total membranes or from outer membranes. 4. It was concluded that liver CPT1 and CPT2 have some epitopes in common and may have a similar subunit size. In addition, CPT1 and the entity that binds malonyl-CoA must be separated polypeptides.