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Chapter 23 . Fatty Acid CatabolismChapter 23Fatty Acid Catabolism. . . . . . . . . . . . . . . . . . . . . . . .Chapter OutlineTriacylglycerol as energy storage moleculeHighly reduced carbon sourceStored without large amounts of waterStored in specialized cells: Adipocytes (adipose or fat cells)Hormonal regulationAdrenaline, glucagon, ACTH mobilize fatty acids from adipocytesHormone binding to surface receptors leads to stimulation of cAMP-dependent protein kinaseTriacylglycerol lipase (hormone-sensitive lipase) activated by phosphorylationTriacylglycerol lipase produces fatty acid and diacylglycerolDiacylglycerol lipase produces fatty acid and monoacylglycerolMonoacylglycerol lipases produces fatty acid and glycerolFatty acids metabolized by -oxidationGlycerol metabolized by glycolysisDietary triacylglycerolsPancreatic lipases secreted into duodenum release fatty acids and glycerolLipase activity dependents on bile salts functioning as detergentsShort-chain fatty acids directly absorbedLong-chain fatty acids recondensed onto glycerol in epithelial cellsResynthesized triacylglycerol complexed to proteinsChylomicrons released into blood-OxidationOxidation of -carbon, cleavage of C- C bondOccurs in mitochondriaTwo-carbon acetate units split off as acetyl-CoAFatty acid activation and transport into mitochondriaShort-chain fatty acidsDiffuse into mitochondriaAcyl-CoA synthetase (Acyl-CoA ligase or fatty acid thiokinase) produces acyl-CoA derivativesATP to AMP + PPi (PPi 2Pi) drives synthesisLong-chain fatty acids: Activated in cytosolAcyl-CoA synthetase produces acyl-CoA derivativesCarnitine acyltransferase I produces acylcarnitineOutside surface of inner mitochondrial membraneCarnitine acyltransferase II reforms acyl-CoAMatrix surface of inner mitochondrial membrane113
Chapter 23 . Fatty Acid CatabolismEnzymology of -oxidation: Four stepsAcyl-CoA dehydrogenaseProduces C-C double bondNoncovalent (but tightly bound) FAD reducedFADH2 passes electrons through electron transfer protein to coenzyme QThree enzymes: Chain-length specificSite of inhibition of hypoglycinEnoyl-CoA hydrase (crotonase)Adds water across double bondThree kinds of enzymesTrans double bond hydrated to L--hydroxyacyl-CoACis double bond hydrated to D--hydroxyacyl-CoATrans double bond hydrated to D--hydroxyacyl-CoAL-Hydroxyacyl-CoA dehydrogenaseOxidizes OHNAD+ reducedThiolase (-ketothiolase)Cleaves off acetyl-CoA unitAcyl-CoA two carbons shorterLast cleavage releasesTwo acetyl-CoA for even carbon numbered chainsOne propionyl-CoA and one acetyl-CoA for odd carbon numbered chainsOdd-chain fatty acids: In plant and marine organism triacylglycerolsPropionyl-CoA converted to succinyl-CoAPropionyl-CoA also from Met, Val, Ile degradationSuccinyl-CoA TCA cycle intermediate: To metabolize completelySuccinyl-CoA to malate