【正文】 but must be emulsified before digestion and transported by special proteins in blood. ? Chemically inert: no undesired chemical reactions with other constituents。 not a major energy source in plants. ? Sources for cells to obtain fatty acids: diet。 triacylglycerols will be used as the energy source for the liver cells, converted to ketone bodies or transported to adipose tissues after being packed with apolipoproteins. 3. Mobilization of stored triacylglycerols in adipocytes needs hormone to signal the demand ? The hormones epinephrine and glucagon, signaling a lack of glucose in the blood, will bind to receptors on adipocyte surface and activate the hormonesensitive lipase and perilipin molecules on the surface of the lipid droplets. ? Fatty acids released are carried to energydemanding tissues (., skeletal muscle, heart, and renal cortex) via the 62 kD monomeric serum albumin (each binding as many as 10 fatty acids). Mobilization of triacylglycerols stored in adipose tissue Entry of glycerol into the glycolytic pathway 4. Early labeling experiments (1904): fatty acids are degraded by sequential removal of twocarbon units ? When dogs were fed with oddnumbered fatty acids attached to a phenyl group, benzoate was excreted。 and when fed with evennumbered, phenylacetate was excreted. ? Hypothesis: the bcarbon is oxidized, with twocarbon units released by each round of oxidation. ? These experiments are a landmark in biochemistry, in using synthetic label (the phenyl group here) to elucidate reaction mechanism, and was done long before radioisotopes was used in biochemistry! Franz Knoop’s labeling experiments (1904): fatty acids are degraded by oxidation at the b carbon, ., b oxidation b b a a 5. Fatty acid oxidation was found to occur in mitochondria ? Enzymes of fatty acid oxidation in animal cells were localized in the mitochondria matrix. ? Revealed by Eugene Kennedy and Albert Lehninger in 1948. 6. Fatty acids are activated on the outer membrane of mitochondria ? Fatty acids are converted to fatty acylCoA (a high energy pound) via a fatty acyladenylate intermediate (enzymebound, mixed anhydride) by the action of fatty acylCoA synthetases (also called fatty acid thiokinase). ? Pyrophosphate is hydrolyzed by inanic pyrophosphatase, thus two anhydride bonds of ATP are consumed to form one highenergy thioester bond, thus pulling the reaction forward: a mon phenomena in biosynthetic reactions. ? Acyladenylates are often formed when –COOH groups are activated in biochemistry. Conversion of a fatty acid to a fatty acylCoA 7. Activated (long chain) fatty acids are carried into the matrix by carnitine ? The fatty acyl group is attached to carnitine (肉堿 ) via transesterification by the action of carnitine acyltransferase I located on the outer membrane of mitochondria, forming fatty acylcarnitine, leaving th