ABSTRACT
We report the molecular basis of familial chylomicronemia and recurrent pancreatitis in five members of a large Dutch family. All patients had normal plasma hepatic lipase and apoC-II levels, but absent lipoprotein lipase (LPL) catalytic activity and low LPL mass in postheparin plasma. The mutation in the LPL gene was characterized as a G715-->A substitution in the last nucleotide of exon 4, resulting in a substitution of Ser for Gly154. PCR amplification of exons 4 + 5 from the patients' mRNA, followed by direct sequencing, revealed normal splicing of intron 4. The mutation creates a BfaI restriction site that allows rapid screening of family members for the mutation. Reproduction of this mutation in LPL-cDNA by site-directed mutagenesis, followed by transient expression in COS-B cells, revealed production of a catalytically inactive enzyme. The Gly154-->Ser substitution appears in a conserved beta-sheet region, in close proximity to Asp156, which is part of the catalytic triad. These studies show that changes to residues close to Asp156 can have profound effects on catalytic activity of LPL.
Subject(s)
Chylomicrons/blood , Glycine , Lipoprotein Lipase/genetics , Pancreatitis/enzymology , Serine , Adult , Base Sequence , Cell Line , DNA/analysis , DNA/chemistry , Humans , Lipoprotein Lipase/chemistry , Male , Molecular Sequence Data , Mutagenesis, Site-Directed , Mutation , Netherlands , Pancreatitis/genetics , RNA Splicing , RNA, Messenger/genetics , Recurrence , TransfectionABSTRACT
The relation between carnitine palmitoyltransferase (CPT) activity and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity was investigated. Rats were treated with aminocarnitine or 1-carnitine overnight. In rats, in which CPT activity was inhibited by aminocarnitine, plasma and hepatic triacylglycerol contents were increased 5- to 6-fold. The plasma cholesterol concentration was unchanged, while the hepatic cholesterol content was lowered (-16%). Hepatic cholesterol synthesis, determined by following the incorporation of 14C-acetate and 3H2O into digitonin-precipitable sterols, in liver slices was increased 5- to 7-fold. HMG-CoA reductase activity in liver microsomes was increased to the same extent.
