• 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 :
β FA cell 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
βββ 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
difusion activation FA 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:
O AMP + PP ATP i O C C ~SCoA OH CoASH
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 (carnitine palmitoyltransferase) FA activation and transport across inner mitochondrial membrane β Oxidation of fatty acids – spiral pathway
Dehydrogenation/ oxidation
Thiolytic Hydration cleavage
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) ββ oxidation oxidation of of unsaturated unsaturated fatty fatty acids acids requiresrequires additional additional enzymes enzymes– – isomerase, NADPH dependent isomerase, NADPH dependent reductasereductase (2,4 dienoyl CoA (2,4 dienoyl CoA reductase), epimerase reductase), epimerase O O
SCoA SCoA
NADPH + H +
Enoyl-CoA 2,4-Dienoyl-CoA isomerase reductase
NADP + O SCoA
SCoA O Example : Oleic acid O C ~SCoA
3 turns of β oxidation cis double bond γγγ β O α C ~SCoA 3 2 1
isomerase ∆3 cis ∆2 trans
O β α C ~SCoA 3 2 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.
ATP + AMP + - H HCO PP COO O 3 i O H3CCC H3CCC propionyl CoA H SCoA carboxylase H SCoA propionyl-CoA D-methylmalonyl-CoA
methylmalonyl CoA epimerase
H H H O O -OOC CCC H3CCC methylmalonyl SCoA - H H CoA mutase COO SCoA succinyl-CoA L-methylmalonyl-CoA Ketone bodiesKetone 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
O CH 3 C CH 2 COO CH 3 CH CH 2 COO O OH 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 O 2 CH C S CoA liver (mitochondrial matrix ) 3 acetoacetyl CoA thiolase CoASH CoASH acetoacetyl CoA O O O
CH 3 C S CoA CH 3 C CH 2 C S CoA
O OH O HMG CoA synthase β α CoASH O C CH 2 C CH 2 C S CoA 5 3 1 βββ hydroxy βββ methylglutaryl CoA (HMG CoA ) CH 3 HMG CoA lyase O O O CH C CH C O CH C S CoA 3 2 acetoacetate 3
CO 2 O NADH+H + CH 3 CH CH 2 COO acetone + CH 3 C CH 3 NAD OH βββ hydroxybutyrate Starvation andStarvation and ketone bodies ketone bodies
hydroxybutyrate acetoacetate
7 6 5 4 3 2
(millimolar) 1 0 Blood Concentration Blood 0 1 2 3 4 Weeks of Starvation Fate of ketoneFate of ketone bodies 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 Only produced in small amounts, eliminated in urine or breath . H+
acetoacetateacetoacetate acetoneacetone
CO 2 Spontaneous loss of CO 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 βββ hydroxybutyrate CH 3 CH CH 2 COO + NAD β hydroxybutyrate dehydrogenase OH NADH+H + O O acetacetate sukcinyl CoA CH 3 C CH 2 C O β ketoacyl CoA transferase O O sukcinát acetoacetyl CoA CH 3 C CH 2 C S CoA CoASH CoASH acetoacetyl CoA thiolase
acetyl CoA O extrahepatic tissues – energy source 2 CH 3 C S CoA
•myokard at physiological conditions CC •skeletal muscles, brain in starvation
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 ketogenesis + lack of oxaloacetate
ketogenesis ketosis ketoacidosis
ketonemia, ketonuria Ketone bodies – excretion from the organism plasma + CH 3 C CH 2 COO + H plasma O acetacetate ketoacidosis
+ CH 3 CH CH 2 COO + H OH acetone β hydroxybutyrate acetacetate + Na +
H2O acetacetate acetone 20% + β hydroxybutyrate + Na H O β hydroxybutyrate 2 aceton 78% 2% • increased water loss + breath moč • loss of Na 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 Oxidationβ α Biosynthesis R CH 2 CH 2 CO S dehydrogenation hydrogenation
R CH = CH 2 CO S
H O hydration + H 2O 2 dehydration
R CH(OH) CH 2 CO S dehydrogenation hydrogenation
R CO CH 2 CO S thiolytic cleavage CoASH condensation
R CO S + CH 3 CO SCoA Differences between FA synthesis and degradation
• Intracellular localization degradation (ß oxidation) mitochondrial matrix biosynthesis cytosol
• Activation of an acyl degradation (ß oxidation ) CoA SH biosynthesis ACP SH (acyl carrier protein, prosthetic group phosphopantheteine )
• Oxidoreduction 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
mitochondrial cytosol matrix oxalacetate acetyl CoA oxalacetate acetyl CoA
inner mitochondrial ADP + Pi membrane citrate lyase citrate synthase ATP CoA CoA citrate 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 + CO 2 Tvorba malonyl CoA Two carbon units are incorporated into a growing chain in the form of malonyl CoA
acetyl CoA carboxylase CH 3 CO~CoA OO C CH 2 CO~S CoA acetyl CoA malonyl CoA
enzyme biotin COO enzyme biotin
ADP+Pi
ATP + CO 2 + enzyme biotin
Acetyl CoA carboxylase kee enzyme of biosynhesis (multienzyme complex)
regulation: allosteric hormonal
+ citrate + insulin
palmitoyl CoA glucagon (product) FA biosynthesis synthesis of palmitate by the fatty acid synthase complex source of other two carbon units 1. two carbon unit 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 Overview of fatty acid metabolism
TAG adipose tissue
HSL chylomicrones TAG GIT Liver TAG VLDL LPL LPL
TAG stored in tissues FA eicosanoids complex lipids ß oxidace biosyntéza ketone bodies cellular membranes acetyl CoA HMG CoA steroids
+ TCA cycle NADH+H , FADH 2 catabolism of carbohydrates and amino acids
ATP respirarory chain