Intermediary metabolism

Vladimíra Kvasnicová

Intermediary metabolism relationships

(saccharides, lipids, proteins)

1. after feeding (energy intake in a diet)

oxidation → CO2, H2O, urea + ATP

formation of stores → glycogen, TAG

Urea

The figures were found (May 2007) at http://www.wellesley.edu/Chemistry/chem227/sugars/oligo/glycogen.jpg http

://students.ou.edu/R/Ben.A.Rodriguez-1/glycogen.gif, http://fig.cox.miami.edu/~cmallery/255/255chem/mcb2.10.triacylglycerol.jpg

Glycogen

reducing end

nonreducing end

Intermediary metabolism relationships

(saccharides, lipids, proteins)

2. during fasting

use of energy stores• glycogen → glucose

• TAG → fatty acids

formation of new energy substrates• gluconeogenesis (glycerol, muscle proteins)

• ketogenesis (storage TAG → FFA → ketone bodies)

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley‑Liss, Inc., New York, 1997. ISBN 0‑471‑15451‑2

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley‑Liss, Inc., New York, 1997. ISBN 0‑471‑15451‑2

Principal metabolic pathways of the intermediary metabolism:

• glycogenesis

• gluconeogenesis

• lipogenesis

• synthesis of FA

• ketogenesis

• proteosynthesis

• urea synthesis

• glycogenolysis

• glycolysis

• lipolysis

-oxidation

• ketone bodies degr.

• proteolysis

• degradation of AA

CITRATE CYCLE, RESPIRATORY CHAIN

Major intermediates

acetyl-Co A

pyruvate

NADH

pyruvate (PDH) – i.e. from glucose

amino acids (degrad.) – from proteins

fatty acids (-oxidation) – from TAG

ketone bodies (degrad.) – from FA

acetyl-CoA

citrate cycle, RCH → CO2, H2O, ATP

synthesis of FAsynthesis of ketone bodies

synthesis of cholesterol synthesis of glucose !!!

aerobic glycolysis

oxidation of lactate (LD)

degradation of some amino acids

pyruvate

acetyl-CoA (PDH)

lactate (lactate dehydrogenase)

alanine (alanine aminotransferase)

oxaloacetate (pyruvate carboxylase)

glucose (gluconeogenesis)

aerobic glycolysisPDH reaction-oxidationcitrate cycle

oxidation of ethanol

NADH

respiratory chain → reoxidation to NAD+

energy storage in ATP! OXYGEN SUPPLY IS NECESSARY!

aerobic glycolysisPDH reaction-oxidationcitrate cycle

oxidation of ethanol

NADH pyruvate → lactate

respiratory chain → reoxidation to NAD+

energy storage in ATP! OXYGEN SUPPLY IS NECESSARY!

The most important is to answer the questions:

WHERE?

WHEN?

HOW?

compartmentalization of the pathways

starve-feed cycle

regulation of the processes

Compartmentalization of mtb pathways

The figure is found at http://fig.cox.miami.edu/~cmallery/150/proceuc/c7x7metazoan.jpg (May 2007)

Cytoplasm• glycolysis• gluconeogenesis (from oxaloacetate or

glycerol)

• metabolism of glycogen• pentose cycle• synthesis of fatty acids• synthesis of nonessential amino acids• transamination reactions • synthesis of urea (a part; only in the liver!)

• synthesis of heme (a part)

• metabolism of purine and pyrimidine nucleotides

Mitochondrion

• pyruvate dehydrogenase complex (PDH)

• initiation of gluconeogenesis -oxidation of fatty acids• synthesis of ketone bodies (only in the liver!) • oxidation deamination of glutamate • transamination reactions• citrate cycle• respiratory chain (inner mitochondrial membrane)

• aerobic phosphorylation (inner mitoch. membrane)

• synthesis of heme (a part)

• synthesis of urea (a part)

Endoplasmic Reticulum

Smooth ER• synthesis of triacylglycerols and phospholipids• elongation and desaturation of fatty acids• synthesis of steroids• biotransformation of xenobiotics• glucose-6-phosphatase

Rough ER• proteosynthesis

(translation and posttranslational modifications)

Golgi Apparatus

• posttranslational modification of proteins• protein sorting • export of proteins (formation of vesicules)

Ribosomes • proteosynthesis

Nucleus• replication and transcription of DNA• synthesis of RNA

Lysosomes

• hydrolysis of proteins, saccharides, lipids and nucleic acids

Peroxisomes

• oxidative reactions involving O2

• use of hydrogen peroxide• degradation of long chain FA (from C20)

Starve-feed cycle

• relationships of the metabolic pathwaysunder various conditions

• cooperation of various tissues

• see also http://www2.eur.nl/fgg/ow/coo/bioch/#english (Metabolic Interrelationships)

1) Well-fed state

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley‑Liss, Inc., New York, 1997. ISBN 0‑471‑15451‑2

2) Early fasting state

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley‑Liss, Inc., New York, 1997. ISBN 0‑471‑15451‑2

3) Fasting state

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley‑Liss, Inc., New York, 1997. ISBN 0‑471‑15451‑2

4) Early refed state

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley‑Liss, Inc., New York, 1997. ISBN 0‑471‑15451‑2

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley‑Liss, Inc., New York, 1997. ISBN 0‑471‑15451‑2

Changes of liver glycogen content

The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley‑Liss, Inc., New York, 1997. ISBN 0‑471‑15451‑2

WELL-FED STATEFASTING STATE

hormones insulin glucagon, adrenaline,

cortisol

response of the body

glycemia lipogenesis

proteosynthesis

glycemia lipolysis

ketogenesis proteolysis

WELL-FED STATEFASTING STATE

hormones insulin glucagon, adrenaline,

cortisol

response of the body

glycemia lipogenesis

proteosynthesis

glycemia lipolysis

ketogenesis proteolysis

source of glucose

from foodfrom stores (glycogen)

gluconeogenesis

fate of glucose

glycolysisformation of stores

glycolysis

WELL-FED STATEFASTING STATE

source of fatty acids

from food TAG from storage TAG

fate of fatty acids

-oxidationsynthesis of TAG

-oxidationketogenesis

WELL-FED STATEFASTING STATE

source of fatty acids

from food TAG from storage TAG

fate of fatty acids

-oxidationsynthesis of TAG

-oxidationketogenesis

source of amino acids

from foodfrom muscle

proteins

fate of amino acids

proteosynthesisoxidation

lipogenesisgluconeogenesis

Metabolism of ammonia- the importance of glutamine -

• synthesis of nucleotides ( nucleic acids)

• detoxification of amino N (-NH2 transport)

• synthesis of citrulline (used in urea cycle):

intake of proteins in a diet (fed state) or

degradation of body proteins (starvation)

concentration of glutamine

• enterocyte: Gln citrulline blood kidneys

• kidneys: citrulline Arg blood liver

• liver: Arg urea + ornithine

ornithine → increased velocity of the UREA CYCLE

= detoxification of NH3 from degrad. of

prot.

General Principles of Regulation

• catabolic / anabolic processes

• last step of each regulation mechanism: change of a concentration of an active enzyme (= regulatory or key enzyme)

• regulatory enzymes often allosteric enzymes

catalyze higly exergonic reactions (irreverzible)

low concentration within a cell

I. Regulation on the organism level

1. signal transmission among cells(signal substances)

2. signal transsduction through the cell membrane

3. influence of enzyme activity:

induction of a gene expression

interconversion of existing enzymes (phosphorylation / dephosphorylation)

II. Regulation on the cell level

1. compartmentalization of mtb pathways

2. change of enzyme concentration(on the level of synthesis of new enzyme )

3. change of enzyme activity(an existing enzyme is activated or inactivated)

1. Compartmentalization of mtb patways

• transport processes between compartments

• various enzyme distribution

• various distribution of substrates and products ( transport)

• transport of coenzymes

• subsequent processes are close to each other

2. Synthesis of new enzyme molecules:

• induction by substrate or repression by product(on the level of transcription)

examples:

xenobiotics induction of cyt P450

heme repression of delta-aminolevulate synthase

3. Change of activity of an existing enzyme

a) in relation to an enzyme kinetics

concentration of substrates ( Km)

availability of coenzymes

consumption of products

pH changes

substrate specificity - different Km

b) activation or inactivation of the enzyme

• covalent modification of the enzymes

interconversion: phosphorylation/dephosphorylation)

cleavage of an precursore (proenzyme, zymogen)

• modulation of activity by modulators (ligands):

feed back inhibition

cross regulation

feed forward activation

3. Change of activity of an existing enzyme

Phosphorylation / dephosphorylation

• some enzymes are active in a phosphorylated form, some are inactive

• phosphorylation:

protein kinases

macroergic phosphate as a donor of the phosphate (ATP!)

• dephosphorylation

protein phosphatase

inorganic phosphate is the product!

The figure is found at: http://stallion.abac.peachnet.edu/sm/kmccrae/BIOL2050/Ch1-13/JpegArt1-13/05jpeg/05_jpeg_HTML/index.htm (December 2006)

Reversible covalent modification:

A)

• phosphorylation by a protein kinase

• dephosphorylation by a protein phosphatase

B)

• phosphorylated enzyme is either active or inactive (different enzymes are influenced differently)

Modulators of enzyme activity(activators, inhibitors)

• isosteric modulation: competitive inhibition

• allosteric modulation:

change of Km or Vmax

T-form (less active) or R-form (more active)

• important modulators: ATP / ADP