Metabolisme LemakSusila Sastri

Fatty acids classification

Metabolisme LemakBiosynthesis of Fatty AcidsOxidation of Fatty AcidsLipolisisLipogenesis

The DifferencesBetween fatty acid biosynthesis and breakdown Intermediates in synthesis are linked to -SH groups of acyl carrier proteins (as compared to -SH groups of CoASynthesis in cytosol; breakdown in mitochondriaEnzymes of synthesis are one polypeptideBiosynthesis uses NADPH/NADP+; breakdown uses NADH/NAD+

Transportation of Digested FatRe-formed into triglyceridesPackaged into chylomicronsLipoprotein lipase breaks down triglycerides in the chylomicronsFatty acids are absorbed by cellsTakes 2-10 hours to clear chylomicron

Lipoproteins

Transport of Synthesized FatsLiver produces some fat and cholesterol from carbohydrate, protein, and free fatty acids taken up from the bloodLiver packages cholesterol and triglycerides for transport as Very Low Density Lipoprotein (VLDL)Remnants of chylomicrons, small and medium FA, and cholesterol get put together to form a VLDL (very low density lipoprotein)Lipoprotein lipase breaks down some triglycerides in VLDL, leaving a Low Density Lipoprotein (LDL)The primary component in an LDL is CholesterolReceptor pathway for cholesterol uptakeScavenger pathway for cholesterol uptake

Composition and properties of human lipoproteinsmost proteins have densities of about 1.3 1.4 g/mL and lipid aggregates usuallyhave densities of about 0.8 g/mL

Lipoprotein classDensity (g/mL)Diameter (nm)Protein % of dry wtPhospholipid %Triacylglycerol % of dry wtHDL1.063-1.215 1533298LDL1.019 1.06318 2825214IDL1.006-1.01925 - 50182231VLDL0.95 1.00630 - 80101850chylomicrons< 0.95100 - 5001 - 2784

Apoproteins of human lipoproteinsA-1 (28,300)- principal protein in HDL90 120 mg% in plasmaA-2 (8,700) occurs as dimer mainly in HDL30 50 mg %B-48 (240,000) found only in chylomicron

C-1 (7,000) found in chylomicron, VLDL, HDL4 7 mg %C-2 (8,800) - found in chylomicron, VLDL, HDL3 8 mg %C-3 (8,800) - found in chylomicron, VLDL, IDL, HDL8 15 mg %D (32,500) - found in HDL8 10 mg %E (34,100) - found in chylomicron, VLDL, IDL HDL3 6 mg %

Apoproteins of human lipoproteins

Metabolic fate of chylomicrons

Metabolic fate of very low density lipoproteins

*Lipoprotein Interactions

Transport of fatty acids from the cytoplasm to the inner mitochondrial space for oxidation.

Pathway of -Oxidation

FATTY ACID SYNTHESISThe synthesis of fatty acids in mammalian systems can be considered as a two-stage process, both stages requiring acetyl-Coenzyme A (acetyl CoA) and both employing multifunctional proteins (multienzyme complexes): stage 1: involves preparation of the key precursor malonyl-CoA by the acetyl CoA carboxylase, stage 2: involves elongation of the fatty acid chain (in 2-carbon increments) by fatty acid synthase.

FATTY ACID SYNTHESIS

The synthesis of one molecule of palmitate requires eight molecules of AcCoA, 7 ATP, and 14 NADH according to the formula:

Regulation oflong-chain fatty acid oxidation in theliver.

Metabolism of adipose tissue

Metabolic ischemia. Glycolysis is the main catabolic pathway during ischemia, whereas fatty acid oxidation is enhanced in this period. As consequence less ATP is generated at the expenses of more protons production, which are ultimately responsible for myocardial acidosis and ions (mainly Calcium) accumulation (see text for more details). Redarrows : enhanced pathway; white arrows : almost abolished pathways

Control of adipose tissue lipolysis

mechanisms in the regulation of cholesterol synthesis

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