Degradation and biosynthesis of fatty acids • Ketone bodies · 2 CH 3-C-CH 2-C-S-CoA O O CoASH CoASH β-hydroxybutyrate dehydrogenase β-ketoacyl-CoA transferase acetoacetyl-CoA

Lipid metabolism

• Degradation and biosynthesis of fattyacids

• 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

ββββ-oxidation: two-carbon fragments successively removedfrom the carboxyl end of activated FA producing

acetyl-CoA entry into TCA cycle ATP

lokalized in the mitochondrial matrix (>18 C perixosomes)

• FA are delivered to cells by diffusion from blood capillaries

• upon entry into the cell FA are immediately activatedby linking them as thioesters to CoASH

• activation is coupled with FA transport throughthe mitochondrial membrane

Fatty acid degradation

C

O

OH

O

~SCoAC

ATP AMP + PPi

CoASH

FA entry into the cell (cytosol) acyl-CoA

transport across the inner mmitochondrial membrane (carnitine shuttle)

acyl-CoA β-oxidace acetyl-CoA TCA cycle

difusion activation

ATP

fatty acyl coenzyme A-synthetase

Fatty acid activation – formation of acyl–CoA:

carnitine

Carnitine shuttle – transport of long-chain FA (>12C)

into the mitochondrial matrix

CAT I

CAT II

CAT – carnitine acyltransferase(carnitine palmitoyltransferase)

Carnitine-acylcarnitinetranslocase

FA activation and transport across inner mitochondrial membrane

β-Oxidation of fatty acids – spiral pathway

Dehydrogenation/oxidation

Hydration

Dehydrogenation/oxidation

Thiolyticcleavage

ET chain2 ATP

ET chain3 ATP

Combination of FA activation, transport into themitochondrial 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 FADH2 2 16

8 (NADH + H+) 3 24

total ATP 147 (146)

β-oxidation of unsaturated fatty acids

requires additional enzymes – isomerase, NADPH-dependentreductase (2,4-dienoyl-CoA reductase), epimerase

β-oxidation of unsaturated fatty acids

requires additional enzymes – isomerase, NADPH-dependentreductase (2,4-dienoyl-CoA reductase), epimerase

O

SCoA

O

SCoA

O

SCoA

O

SCoA

Enoyl-CoAisomerase

2,4-Dienoyl-CoAreductase

NADP+

NADPH + H+

Oleic acid

isomerase∆3 cis ∆2 trans

~SCoA

O

C

α ~SCoAC

O

3 2 1

βγγγγ

12

βO

~SCoACα

3

cis-double bond 3 turns of β-oxidation

Example:

Unsaturated FA provide less energy than saturated FA –less reducing equivalents (FADH2) are produced

hydration dehydrogenation ….

H3C C C

H

H SCoA

O

H3C C C

COO-

H

O

SCoA

H3C C C

H

COO-

O

SCoA

C C C

H

H

O

SCoA

H

H

-OOC

propionyl-CoA D-methylmalonyl-CoA

L-methylmalonyl-CoAsuccinyl-CoA

propionyl-CoAcarboxylase

methylmalonyl-CoA epimerase

methylmalonyl-CoA mutase

ATP +HCO3

-

AMP +PPi

β-oxidation of FA with an odd number of carbon

They can be handled normally until the last step where propionyl CoAis produced.Three reactions are required to convert propionyl CoA to succinyl CoAwhich can enter to the TCA cycle.

• 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 bodiesKetone bodies

synthesis = ketogenesis

localization: liver, mitochondrial matrix

initial substrate: acetyl-CoA

function: energy source

physiological conditions - myocard

starvation - skeletal muscles

brain

Ketone bodies

β-hydroxybutyrateacetacetate acetone

CH3-C-CH2-COO-

O

CH3-CH-CH2-COO-

OH CH3-C-CH3

O

Formation and utilization of ketone bodies

enters into TCA cycle ATP

Ketogenesisliver(mitochondrial matrix) CH3-C- S-CoA

O

CH3-C-CH2-C-S-CoA

O O

CH3-C-S-CoA

O

CH3-C-CH2-C-O-

O O

CH3-C-S-CoA

O

CH3-C-CH3

O CH3-CH-CH2-COO-

OH

acetoacetyl-CoA

ββββ-hydroxy-ββββ-methylglutaryl-CoA (HMG-CoA)

acetoacetate

acetone

ββββ-hydroxybutyrate

2

CoASHCoASH

acetoacetyl-CoA thiolase

CoASH

CO2NADH+H+

NAD+

HMG-CoA synthase

HMG-CoA lyase

αβ

135-O-C-CH2-C--CH2-C-S-CoA

O OOH

CH3

Starvation and ketone bodiesStarvation and ketone bodies

0

1

2

3

4

5

6

7

0 1 2 3 4

hydroxybutyrate acetoacetate

Weeks of Starvation

Blo

od

Co

nce

ntr

atio

n(m

illim

ola

r)

Fate of ketone bodiesFate of ketone bodies

• Acetoacetate and β-hydroxybutyrateProduced 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.

Spontaneous loss of CO2 from acetoacetate.It can be detected in the breath - acetone breathSymptom of untreated diabetes mellitus or starvation conditions.

acetoacetateacetoacetateacetoneacetone

H+

CO2

Utilization of ketone bodies in extrahepatic tissues

CH3-CH-CH2-COO-

OH

acetacetate

acetoacetyl-CoA

acetyl-CoA

ββββ-hydroxybutyrate

NADH+H+

NAD+

sukcinyl-CoA CH3-C-CH2-C-O-

O O

sukcinát

CH3-C-S-CoA

O

2

CH3-C-CH2-C-S-CoA

O O

CoASHCoASH

β-hydroxybutyrate dehydrogenase

β-ketoacyl-CoA transferase

acetoacetyl-CoA thiolase

CC

ATP

extrahepatic tissues – energy source

•myokard at physiological conditions•skeletal muscles, brain in starvation

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-CoAketogenesis

+ lack of oxaloacetate

ketogenesis ketosis ketoacidosis

ketonemia, ketonuria

Ketone bodies – excretion from the organism

acetacetate

acetone

acetacetate20%

β-hydroxybutyrate

β-hydroxybutyrate78%

acetone

aceton2%

ketoacidosis

β-hydroxybutyrate +

acetacetate +

• increased water loss• loss of Na+

Na+

H2O

-

Na+

H2O

-

breathbreath močmoč urineurine

plasmaplasma

CH3-CH-CH2-COO- + H+

OH

CH3-C-CH2-COO- + H+

O

plasmaplasma

Biosynthesis of fatty acids

initial substrate: acetyl-CoA

tissues:liveradipose tissuelactating 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-Oxidation BiosynthesisR- CH2 - CH2 - CO- S -

R- CH = CH2 - CO - S -

R- CH(OH) - CH2 - CO - S -

R - CO - CH2 - CO - S -

R - CO - S - + CH3- CO - SCoA

dehydrogenation

hydration

dehydrogenation

thiolytic cleavage

hydrogenation

dehydration

hydrogenation

condensation

+ H2O - H2O

CoASH

β α

Differences between FA synthesis and degradation

• Intracellular localizationdegradation (ß-oxidation) - mitochondrial matrixbiosynthesis - cytosol

• Activation of an acyldegradation (ß-oxidation) - CoA-SHbiosynthesis - ACP-SH (acyl carrier protein, prosthetic group

phosphopantheteine)

• Oxidoreduction cofactorsdegradation (ß-oxidation) - NAD+, FADbiosynthesis - NADPH + H+

• Biosynthesisgrowth of an FA chain catalyzed by 1 multifunctional enzyme (containsaktive 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 CoAdonor of two-carbon unit in each turn

Production of cytosolic acetyl-CoATransport of acetyl-CoA from mitochondrial matrix to cytosol in the form of citrate

cytosol

citrate

CoA

citrate lyaseADP + Pi

ATP

oxalacetate acetyl-CoA

inner mitochondrialmembrane

oxalacetate acetyl-CoA

citrate

CoA

citrate synthase

mitochondrial

matrix

Sources of cytosolic NADPH- pentose phosphate pathway – oxidative phase- oxidation of malate – malate dehydrogenase dekarboxylating (malic enzyme):

oxalacetate malate pyruvate + CO2

NADP+ NADPH+ H+

at high concntration of mitochondrial citrate, isocitrate dehydrogenase inhibited by ATP

Tvorba malonyl-CoATwo-carbon units are incorporated into a growing chain in the form of malonyl-CoA

Acetyl CoA carboxylase - kee enzyme of biosynhesis (multienzyme complex)

CH3-CO~CoA-OOC-CH2 -CO~S-CoA

acetyl-CoA malonyl-CoA

enzyme-biotin-COO- enzyme-biotin

ATP + CO2 + enzyme-biotin

ADP+Pi

regulation: allosteric

citrate

palmitoyl-CoA(product)

hormonal

insulin

glucagon

+

-

+

-

acetyl CoA carboxylase

FA biosynthesis - synthesis of palmitate by thefatty acid synthase complex

1. two-carbon unit

source of other two-carbon unitsfor chain growth

Regulation of fatty acid metabolism

• Supply of fatty acids - liver FA - ß-oxidationat oxalacetate - citrate - ketogenesis

adipocyte FA - TAG synthesis

• ATP citrate (glucose supply – after meal, inhibited isocitratedehydrogenase in TCA cycle) – after translocation

to cytosol citrate activates acetyl CoA carboxylase - FA synthesis

• Malonyl-CoA - inhibits carnitine acyltransferase I – long-chain FA cannot enterinto mitochondria - ß-oxidation- FA accumulate in cytosol - TAG synthesis

• Palmitoyl-CoA - inhibits mitochndrial translocase for citrate – citratedo 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 expresionfood supply after fasting - expression of acetyl CoAcarboxylase, fatty acid synthase - FA synthesis

FA

Liver TAG VLDL chylomicrones TAG GIT

TAG - adipose tissue

acetyl-CoA

TCA cycle

respirarory chain

NADH+H+, FADH2

TAG stored in tissues

complex lipids

cellular membranes

catabolism of carbohydratesand amino acids

HMG CoA

ketone bodies

steroids

eicosanoids

LPL LPL

HSL

ßß--oxidaceoxidacebiosyntézabiosyntéza

Overview of fatty acid metabolism

ATP