Lipid metabolism Degradation and biosynthesis of fatty acids Ketone bodies
Fatty acids (FA) primary fuel molecules in the fat category main use is for long-term energy storage high level of energy storage: fats - 38 kj/g, carbohydrates 16 kj/g Primary sources of FA: - dietary triacylglycerols - triacylglycerols synthesized in the liver - triacylglycerols stored in adipocytes FA must be delivered to cells where β-oxidation occurs: FA cell β-oxidation ATP liver heart skeletal muscles
Fatty acid degradation - β-oxidation FA are delivered to cells by diffusion from blood capillaries upon entry into the cell FA are immediately activated by linking them as thioesters to CoASH activation is coupled with FA transport through the mitochondrial membrane β-oxidation: two-carbon fragments successively removed from the carboxyl end of activated FA producing acetyl-coa entry into TCA cycle ATP lokalized in the mitochondrial matrix (>18 C perixosomes)
Fatty acid degradation FA difusion activation entry into the cell (cytosol) acyl-coa transport across the inner mmitochondrial membrane (carnitine shuttle) acyl-coa β-oxidace acetyl-coa TCA cycle ATP Fatty acid activation formation of acyl CoA: C H ATP CoASH AMP + PP i C~SCoA fatty acyl coenzyme A-synthetase
Carnitine shuttle transport of long-chain FA (>12C) into the mitochondrial matrix Carnitine-acylcarnitine translocase CAT I CAT II CAT carnitine acyltransferase (carnitine palmitoyltransferase) carnitine
FA activation and transport across inner mitochondrial membrane
β-xidation of fatty acids spiral pathway Dehydrogenation/ oxidation Thiolytic cleavage Hydration ET chain 2 ATP Dehydrogenation/ oxidation ET chain 3 ATP
Combination of FA activation, transport into the mitochondrial matrix, β-oxidation and TCA cycle
Energy yield from β-oxidation of saturated FA example: stearic acid, 18 C 9 acetyl-coa, 8 turns of β-oxidation ATP/unit ATP produced activation -1(-2) -1(-2) 9 acetyl CoA TCA 12 108 8 FADH 2 2 16 8 (NADH + H + ) 3 24 total ATP 147 (146)
β-oxidation of unsaturated fatty acids requires additional enzymes isomerase, NADPH-dependent reductase (2,4-dienoyl-CoA reductase), epimerase SCoA SCoA NADPH + H + Enoyl-CoA isomerase 2,4-Dienoyl-CoA reductase NADP + SCoA SCoA
Example: leic acid C ~SCoA cis-double bond γ β α C 3 2 1 ~SCoA 3 turns of β-oxidation isomerase 3 cis 2 trans β 3 α 2 C~SCoA 1 hydration dehydrogenation. Unsaturated FA provide less energy than saturated FA less reducing equivalents (FADH 2 ) are produced
β-oxidation of FA with an odd number of carbon They can be handled normally until the last step where propionyl CoA is produced. Three reactions are required to convert propionyl CoA to succinyl CoA which can enter to the TCA cycle. H H 3 C C C H SCoA propionyl-coa ATP + HC 3 - propionyl-coa carboxylase AMP + PP i C - H 3 C C C H SCoA D-methylmalonyl-CoA H H - C C C C H H SCoA succinyl-coa methylmalonyl- CoA mutase H H 3 C C C methylmalonyl- CoA epimerase C - SCoA L-methylmalonyl-CoA
Ketone bodies After degradation of a fatty acid, acetyl CoA is further oxidized in the citric acid cycle. First step in the citric acid cycle acetyl CoA + oxaloacetate citrate If too much acetyl CoA is produced from β-oxidation, some is converted to ketone bodies.
Ketone bodies CH 3 -C-CH 2 -C - CH 3 -CH-CH 2 -C - H CH 3 -C-CH 3 acetacetate β-hydroxybutyrate acetone synthesis = ketogenesis localization: liver, mitochondrial matrix initial substrate: acetyl-coa function: energy source physiological conditions - myocard starvation - skeletal muscles brain
Formation and utilization of ketone bodies enters into TCA cycle ATP
Ketogenesis liver(mitochondrial matrix) CH 3 -C-CH 3 acetone 2 CH 3 -C- S-CoA acetoacetyl-coa thiolase CoASH CoASH acetoacetyl-coa CH 3 -C-S-CoA CH 3 -C-CH 2 -C-S-CoA H β α HMG-CoA synthase CoASH - -C-CH 2 -C--CH 2 -C-S-CoA 5 3 1 β-hydroxy-β-methylglutaryl-coa (HMG-CoA) CH 3 HMG-CoA lyase CH 3 -C-CH 2 -C- - CH 3 -C-S-CoA acetoacetate C 2 NADH+H + CH 3 -CH-CH 2 -C - NAD + H β-hydroxybutyrate
Starvation and ketone bodies hydroxybutyrate acetoacetate Blood Concentration (millimolar) 7 6 5 4 3 2 1 0 0 1 2 3 4 Weeks of Starvation
Fate of ketone bodies Acetoacetate and β-hydroxybutyrate Produced in the liver, diffuse in blood to other tissues. Primarily transported to muscles and brain for use as energy sources after reconverion to acetyl CoA Acetone nly produced in small amounts, eliminated in urine or breath. H + acetoacetate acetone C 2 Spontaneous loss of C 2 from acetoacetate. It can be detected in the breath - acetone breath Symptom of untreated diabetes mellitus or starvation conditions.
Utilization of ketone bodies in extrahepatic tissues CH 3 -CH-CH 2 -C - H CH 3 -C-CH 2 -C-S-CoA β-hydroxybutyrate NAD + NADH+H + acetacetate sukcinyl-coa CH 3 -C-CH 2 -C- - sukcinát β-ketoacyl-coa transferase acetoacetyl-coa CoASH CoASH β-hydroxybutyrate dehydrogenase acetoacetyl-coa thiolase acetyl-coa extrahepatic tissues energy source 2 CH 3 -C-S-CoA myokard at physiological conditions skeletal muscles, brain in starvation CC ATP
Utilization of ketone bodies produced in the liver, HEART, (BRAIN)
Abnormal production of ketone bodies: starvation, I. type diabetes mellitus, alcoholism secretion of glucagon activation of hormone sensitive lipase in adipocyte increased lipolysis in adipose tissue increased entry of FA into the liver ß-oxidation high production of acetyl-coa + lack of oxaloacetate ketogenesis ketogenesis ketosis ketoacidosis ketonemia, ketonuria
Ketone bodies excretion from the organism plasma acetacetate CH 3 -C-CH 2 -C - + H + plasma ketoacidosis acetone β-hydroxybutyrate CH 3 -CH-CH 2 -C - + H + H acetacetate + - Na + H 2 acetone breath aceton 2% acetacetate 20% β-hydroxybutyrate 78% moč β-hydroxybutyrate + increased water loss loss of Na + - Na + H 2 urine
Biosynthesis of fatty acids initial substrate: acetyl-coa tissues: liver adipose tissue lactating mammary gland intracellular localization: cytosol - palmitic acid (C16) ER, mitochondria - elongation (C18 - C24) ER - desaturation palmitooleic acid (C16) oleic acid (C18) arachidonic acid (C20) Reactions of FA biosynthesis- reversal course of FA ß-oxidation
ß-xidation β α R- CH 2 - CH 2 - C- S - Biosynthesis dehydrogenation R- CH = CH 2 - C - S - hydrogenation hydration + H 2 - H 2 dehydration R- CH(H) - CH 2 - C - S - dehydrogenation hydrogenation thiolytic cleavage R - C - CH 2 - C - S - CoASH condensation R - C - S - + CH 3 - C - SCoA
Differences between FA synthesis and degradation Intracellular localization degradation (ß-oxidation) biosynthesis - mitochondrial matrix - cytosol Activation of an acyl degradation (ß-oxidation) - CoA-SH biosynthesis - ACP-SH (acyl carrier protein, prosthetic group phosphopantheteine) xidoreduction cofactors degradation (ß-oxidation) - NAD +, FAD biosynthesis - NADPH + H + Biosynthesis growth of an FA chain catalyzed by 1 multifunctional enzyme (contains aktive sites for all reactions of the synthesis) fatty acid synthase 1. reaction of synthesis distinct from a reversal reaction of degradation malonyl CoA + acetyl CoA acetyl CoA + acetyl CoA donor of two-carbon unit in each turn
Production of cytosolic acetyl-coa Transport of acetyl-coa from mitochondrial matrix to cytosol in the form of citrate cytosol oxalacetate acetyl-coa mitochondrial matrix oxalacetate acetyl-coa citrate lyase CoA citrate ADP + P i ATP inner mitochondrial membrane citrate synthase CoA citrate at high concntration of mitochondrial citrate, isocitrate dehydrogenase inhibited by ATP Sources of cytosolic NADPH - pentose phosphate pathway oxidative phase - oxidation of malate malate dehydrogenase dekarboxylating (malic enzyme): NADP + NADPH+ H + oxalacetate malate pyruvate + C 2
Tvorba malonyl-coa Two-carbon units are incorporated into a growing chain in the form of malonyl-coa CH 3 -C~CoA acetyl-coa acetyl CoA carboxylase - C-CH 2 -C~S-CoA malonyl-coa enzyme-biotin-c - enzyme-biotin ADP+P i ATP + C 2 + enzyme-biotin Acetyl CoA carboxylase - kee enzyme of biosynhesis (multienzyme complex) regulation: allosteric hormonal + citrate + insulin - palmitoyl-coa (product) - glucagon
1. two-carbon unit FA biosynthesis - synthesis of palmitate by the fatty acid synthase complex source of other two-carbon units for chain growth
Regulation of fatty acid metabolism Supply of fatty acids - liver FA - ß-oxidation at oxalacetate - citrate - ketogenesis adipocyte FA - TAG synthesis ATP citrate (glucose supply after meal, inhibited isocitrate dehydrogenase in TCA cycle) after translocation to cytosol citrate activates acetyl CoA carboxylase - FA synthesis Malonyl-CoA - inhibits carnitine acyltransferase I long-chain FA cannot enter into mitochondria - ß-oxidation - FA accumulate in cytosol - TAG synthesis Palmitoyl-CoA - inhibits mitochndrial translocase for citrate citrate do not enter into cytosol - FA synthesis
Regulation of fatty acid metabolism Hormonal regulation: Insulin - dephosphorylation of acetyl CoA carboxylase (= activation) FA synthesis Glukagon - phosphorylation of acetyl CoA carboxylase (= inaktivace) - FA synthesis - imcreased lipolysis in adipose tissue - entry of FA into liver ß-oxidation Adaptive control - changes in enzyme expresion food supply after fasting - expression of acetyl CoA carboxylase, fatty acid synthase - FA synthesis
TAG - adipose tissue HSL Liver TAG VLDL LPL LPL chylomicrones TAG GIT TAG stored in tissues complex lipids cellular membranes verview of fatty acid metabolism ß-oxidace FA biosyntéza acetyl-coa eicosanoids HMG CoA ketone bodies steroids catabolism of carbohydrates and amino acids TCA cycle NADH+H +, FADH 2 ATP respirarory chain