The inhibition of lysolecithin:lysolecithin acyltransferase by several specific reagents was studied. Diisopropyl fluorophosphate (DFP) completely inhibited both activities at a concentration of 4 mM. Activity was not protected by substrate and the enzyme showed a change in circular dichroism spectrum upon treatment with inhibitor. Phenylmethanesulfonyl fluoride, another serine-specific reagent, did not inhibit either hydrolysis or transacylation. Therefore, we suggest that DFP does not modify an active serine in the catalytic site. p-Hydroxymercury benzoate and N-ethylmaleimide (NEM) abolished both activities of the enzyme. The presence of substrate partially protected against inactivation. Far-uv CD spectrum of NEM-modified enzyme revealed no changes in protein structure. The existence of two classes of essential cysteine residues was deduced from kinetics of NEM inactivation. Both classes differ in NEM reactivity and also in their participation in the catalytic mechanism. A tyrosine-specific reagent, tetranitromethane, also inhibited hydrolysis and transacylation, following first-order kinetics. The partial protection by substrate suggested the possible existence of essential tyrosines near the active site. At pH 5.0 N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline inactivated hydrolysis but not transacylation. However, both of them remained unchanged at pH 6.5. The substrate prevented the loss of hydrolytic ability. Therefore, a carboxyl residue participating just in the catalytic mechanism of hydrolysis is proposed.
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http://dx.doi.org/10.1016/0003-9861(90)90553-b | DOI Listing |
J Lipid Res
July 2024
Department of Internal Medicine, University of Michigan, Ann Arbor, MI, USA. Electronic address:
Bis(monoacylglycerol)phosphate (BMP) is an acidic glycerophospholipid localized to late endosomes and lysosomes. However, the metabolism of BMP is poorly understood. Because many drugs that cause phospholipidosis inhibit lysosomal phospholipase A2 (LPLA2, PLA2G15, LYPLA3) activity, we investigated whether this enzyme has a role in BMPcatabolism.
View Article and Find Full Text PDFJ Pharm Biomed Anal
August 2024
Department of Metabolism, Digestion and Reproduction, Faculty of Medicine, Imperial College London, Burlington Danes Building, London W12 0NN, UK. Electronic address:
Drugs and drug metabolites containing a carboxylic-acid moiety can undergo in vivo conjugation to form 1-β-O-acyl-glucuronides (1-β-O-AGs). In addition to hydrolysis, these conjugates can undergo spontaneous acyl migration, and anomerisation reactions, resulting in a range of positional isomers. Facile transacylation has been suggested as a mechanism contributing to the toxicity of acyl glucuronides, with the kinetics of these processes thought to be a factor.
View Article and Find Full Text PDFBiochim Biophys Acta Mol Cell Biol Lipids
May 2024
Institute of Molecular Biosciences, University of Graz, 8010 Graz, Austria; Field of Excellence BioHealth, University of Graz, 8010 Graz, Austria; BioTechMed-Graz, 8010 Graz, Austria. Electronic address:
Biochim Biophys Acta Mol Cell Biol Lipids
March 2024
Institute of Molecular Biosciences, University of Graz, 8010 Graz, Austria; Field of Excellence BioHealth, University of Graz, 8010 Graz, Austria; BioTechMed-Graz, 8010 Graz, Austria. Electronic address:
Patatin-like phospholipase domain containing proteins (PNPLAs) play diverse roles in lipid metabolism. In this review, we focus on the enzymatic properties and predicted 3D structures of PNPLA1-5. PNPLA2-4 exert both catabolic and anabolic functions.
View Article and Find Full Text PDFBull Math Biol
August 2023
Institute of Molecular Biosciences, University of Graz, Humboldtstraße 50, 8010, Graz, Austria.
Fatty acids (FAs) are crucial energy metabolites, signalling molecules, and membrane building blocks for a wide range of organisms. Adipose triglyceride lipase (ATGL) is the first and presumingly most crucial regulator of FA release from triacylglycerols (TGs) stored within cytosolic lipid droplets. However, besides the function of releasing FAs by hydrolysing TGs into diacylglycerols (DGs), ATGL also promotes the transacylation reaction of two DG molecules into one TG and one monoacylglycerol molecule.
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