Pig Liver Carnitine Palmitoyltransferase I, with Low Km for Carnitine and High Sensitivity to Malonyl-CoA Inhibition, Is a Natural Chimera of Rat Liver and Muscle Enzymes

• Published in: Biochemistry (Easton) Vol. 40; no. 7; pp. 2260 - 2266
• Main Authors: NICOT, Carine, HEGARDT, Fausto G., WOLDEGIORGIS, Gebre, HARO, Diego, MARRERO, Pedro F.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 20-02-2001
• Subjects: Amino Acid Sequence; Animals; Base Sequence; Carnitine - analogs & derivatives; Carnitine - metabolism; Carnitine O-Palmitoyltransferase - antagonists & inhibitors; Carnitine O-Palmitoyltransferase - biosynthesis; Carnitine O-Palmitoyltransferase - genetics; Carnitine O-Palmitoyltransferase - metabolism; Cloning, Molecular; DNA, Complementary - isolation & purification; Enzyme Inhibitors - metabolism; Humans; Isoenzymes - antagonists & inhibitors; Isoenzymes - biosynthesis; Isoenzymes - genetics; Isoenzymes - metabolism; Kinetics; Malonyl Coenzyme A - metabolism; Mice; Mitochondria, Liver - enzymology; Mitochondria, Muscle - enzymology; Molecular Sequence Data; Organ Specificity - genetics; Pichia - genetics; Rats; Sequence Alignment; Swine
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi0024106

The outer mitochondrial membrane enzyme carnitine palmitoyltransferase I (CPTI) catalyzes the initial and regulatory step in the beta-oxidation of fatty acids. The genes for the two isoforms of CPTI-liver (L-CPTI) and muscle (M-CPTI) have been cloned and expressed, and the genes encode for enzymes with very different kinetic properties and sensitivity to malonyl-CoA inhibition. Pig L-CPTI encodes for a 772 amino acid protein that shares 86 and 62% identity, respectively, with rat L- and M-CPTI. When expressed in Pichia pastoris, the pig L-CPTI enzyme shows kinetic characteristics (carnitine, K(m) = 126 microM; palmitoyl-CoA, K(m) = 35 microM) similar to human or rat L-CPTI. However, the pig enzyme, unlike the rat liver enzyme, shows a much higher sensitivity to malonyl-CoA inhibition (IC(50) = 141 nM) that is characteristic of human or rat M-CPTI enzymes. Therefore, pig L-CPTI behaves like a natural chimera of the L- and M-CPTI isotypes, which makes it a useful model to study the structure--function relationships of the CPTI enzymes.