Biochemistry for nurses: Unit 3
THE PROTEIN METABOLISM
Biochemistry for nurses: Unit 3
• Protein Turnover = Continuous degradation and synthesis of proteins. Replacement of 1-2% of the total body protein each day• Amino acid pool = Accumulation of free AA in the liver and the blood: 75 % of
liberated AA from tissue proteins are reutilized• Degradation (catabolism of AA) = Excess of AA are not stored! but rapidly
degraded for the synthesis of glucose (glycolosis) and lipids. Degradation of excess AA causes an excess of nitrogen.
• Waste = Nitrogen excess is transformed into urea (80%) and ammonium (NH4+) in
order to be thrown away in the urine.
(Liver and Blood)
Biochemistry for nurses: Unit 3
NITROGEN BALANCE
• The amino acids are the main source of Nitrogen.
• Nitrogen balance (NB) is a comparaison between nitrogen intake (Dietary proteins) and nitrogen loss (indigested proteins in feces, waste excretion as urea (80%) and ammonia (NH4
+) in the urine).
- For normal adult: Ingested nitrogen = excreted nitrogen - Positive NB = Ingested nitrogen > excreted nitrogen
(children growth, pregnancy)- Negative NB = Ingested nitrogen < excreted nitrogen
(may follow surgery, advanced cancer, marasmus)
Biochemistry for nurses: Unit 3
• Protein Turnover = Continuous degradation and synthesis of proteins. Replacement of 1-2% of the total body protein each day• Amino acid pool = Accumulation of free AA in the liver and the blood: 75 % of
liberated AA from tissue proteins are reutilized• Degradation (catabolism of AA) = Excess of AA are not stored! but rapidly
degraded for the synthesis of glucose (glycolosis) and lipids. Degradation of excess AA causes an excess of nitrogen.
• Waste = Nitrogen excess is transformed into urea (80%) and ammonium (NH4+) in
order to be thrown away in the urine.
(Liver and Blood)
Biochemistry for nurses: Unit 3
Digestion and absorption of proteins
Digestion = degradation of the protein into AA by the digestive system to make it absorbable by intestine.
Absorption = Transfert of the AA from the intestine to the blood
Biochemistry for nurses: Unit 3
• Proteins are digested by proteases and peptidases. • Protein digestion starts in the stomach.• PEPSIN is an endoprotease which degrades food proteins in the stomach.
Biochemistry for nurses: Unit 3
Biochemistry for nurses: Unit 3
• TRYPSIN = Endopeptidase cleaves the peptide bond at the carboxyl side of the Lysine and Arginine.
• CHYMOTRYPSIN = Endopeptidase cleaves the peptide bond at the carboxyl side of the Tryptophan, Tyrosine and Phenylalanine.
Biochemistry for nurses: Unit 3
Protein digestion is completed in the small intestine by brush border enzymes carboxypeptidase, aminopeptidase, and dipeptidase.
Biochemistry for nurses: Unit 3
Biochemistry for nurses: Unit 3
Practise
ENDOPEPTIDASE:• Trypsin = cleaves at the COOH side of Lysine and Arginine.• Chymotrypsin = cleaves at the COOH side of Tryptophan, Tyrosine
and Phenylalanine.• Tri or Dipeptidase = cleaves between AA of tri or dipeptidesEXOPEPTIDASE:• Carboxypeptidase = removes AA from the COOH end• Aminopeptidase = removes AA from the NH2 end
H2N-Val-Cys-Ala-Leu-Lys-Val-Glu-Arg-Gly-Phe-Phe-Tyr-Thr-Pro-Lys-Ala-COOH
Trypsin + Chymotrypsin
?Tripeptidase + Aminopeptidase + Carboxypeptidase
Final products ?
Biochemistry for nurses: Unit 3
H2N-Val-Cys-Ala-Leu-Lys-Val-Glu-Arg-Gly-Phe-Phe-Tyr-Thr-Pro-Lys-Ala-COOH
Trypsin
Biochemistry for nurses: Unit 3
H2N-Val-Cys-Ala-Leu-Lys-Val-Glu-Arg-Gly-Phe-Phe-Tyr-Thr-Pro-Lys-Ala-COOH
ChymotrypsinTrypsin
Biochemistry for nurses: Unit 3
H2N-Val-Cys-Ala-Leu-Lys-Val-Glu-Arg-Gly-Phe-Phe-Tyr-Thr-Pro-Lys-Ala-COOH
ChymotrypsinTrypsin
H2N-Val-Cys-Ala-Leu-Lys-COOH
H2N-Val-Glu-Arg-COOH
H2N-Gly-Phe-COOH
H2N-Phe-COOH
H2N-Tyr-COOH
H2N-Thr-Pro-Lys-COOH
H2N-Ala-COOH
Biochemistry for nurses: Unit 3
H2N-Val-Cys-Ala-Leu-Lys-COOH
H2N-Val-Glu-Arg-COOH
H2N-Gly-Phe-COOH
H2N-Phe-COOH
H2N-Tyr-COOH
H2N-Thr-Pro-Lys-COOH
H2N-Ala-COOH
Tripeptidase
Biochemistry for nurses: Unit 3
H2N-Val-Cys-Ala-Leu-Lys-COOH
H2N-Val-Glu-Arg-COOH
H2N-Gly-Phe-COOH
H2N-Phe-COOH
H2N-Tyr-COOH
H2N-Thr-Pro-Lys-COOH
H2N-Ala-COOH
Tripeptidase + Aminopeptidase
Biochemistry for nurses: Unit 3
H2N-Val-Cys-Ala-Leu-Lys-COOH
H2N-Val-Glu-Arg-COOH
H2N-Gly-Phe-COOH
H2N-Phe-COOH
H2N-Tyr-COOH
H2N-Thr-Pro-Lys-COOH
H2N-Ala-COOH
Tripeptidase + Aminopeptidase + Carboxypeptidase
Biochemistry for nurses: Unit 3
H2N-Val-Cys-Ala-Leu-Lys-COOH
H2N-Val-Glu-Arg-COOH
H2N-Gly-Phe-COOH
H2N-Phe-COOH
H2N-Tyr-COOH
H2N-Thr-Pro-Lys-COOH
H2N-Ala-COOH
Tripeptidase + Aminopeptidase + Carboxypeptidase
H2N-Val-COOH
H2N-Cys-Ala-Leu-COOH
H2N-Lys-COOH
H2N-Val-COOH
H2N-Glu-COOH
H2N-Arg-COOH
H2N-Gly-Phe-COOH
H2N-Phe-COOH
H2N-Tyr-COOH
H2N-Thr-COOH
H2N-Pro-COOH
H2N-Lys-COOH
H2N-Ala-COOH
Biochemistry for nurses: Unit 3
Summary:
Biochemistry for nurses: Unit 3
• Protein Turnover = Continuous degradation and synthesis of proteins. Replacement of 1-2% of the total body protein each day
• Amino acid pool = Dietary proteins and the catabolism of tissue proteins provide free AA. 75 % of liberated AA from tissue proteins are reutilized.
• Degradation (catabolism of AA) = Excess of AA are not stored! but rapidly degraded for the synthesis of glucose (glycolosis) and lipids. Degradation of excess AA causes an excess of nitrogen.
• Waste = Nitrogen excess is transformed into urea (80%) and ammonium (NH4
+) in order to be thrown away in the urine.
(Liver and Blood)
Biochemistry for nurses: Unit 3
Definition of the Keto Acid• The deamination of an Amino Acid (= removing of the amino group)
forms the corresponding Keto Acid. • The Keto acid is also called « the carbon skeleton »
Biochemistry for nurses: Unit 3
Definition of the Keto Acid• The deamination of an Amino Acid (= removing of the amino group)
forms the corresponding Keto Acid. • The Keto acid is also called « the carbon skeleton »
WASTE
REUSED!
Biochemistry for nurses: Unit 3
BIOSYNTHESIS of UREA
Biosynthesis of urea is composed by 4 stages:
1. Transamination2. Oxidative deamination of
Glutamate3. Ammonia transport4. Reactions of the urea cycle.
80% of the excess amino acid nitrogen forms Urea in order to
be thrown away in the urine.
Tissues
Liver
Biochemistry for nurses: Unit 3
Transamination• Transfert of the α-amino group (NH2) to the ketoglutarate to give GLUTAMATE• The reaction is reversible.• The reaction is catalysed by an enzyme (Aminotransferase) in presence of a co-enzyme (PLP = Vit B6)
(TISSUES)
Biochemistry for nurses: Unit 3
Oxidative deamination of Glutamate • Formation of ammonia (NH3) from the amino group (NH2) of the Glutamate by oxidative deamination.• Glutamate is the only Amino Acid that undergoes oxidative deamination.• Enzyme = Glutamate Dehydrogenase (GDH); Coenzyme = NAD+
(LIVER)
Biochemistry for nurses: Unit 3
Amino acid oxidase reaction
• The amino acid oxidase (AAO) of liver and kidney removes the nitrogen as
ammonium ion (NH4+).
• Conversion of Amino Acids to an Imino acids which are decomposed to a Keto acid with release of NH4
+.
• Enzyme = AAO ; Coenzyme = Flavin
• The reduced Flavin is reoxidized by O2, forming hydrogen peroxide (H2O2) which then is split to O2 and H2O by CATALASE.
(LIVER and KIDNEY)
Biochemistry for nurses: Unit 3
Ammonia (NH3) Transport
• NH3 is very toxic to the nervous system!
• The NH3 produced by tissue are rapidly removed from circulation by the Liver and converted to UREA
• Only traces (10-20 uG/dL) of NH3 are present in blood in normal conditions
• Liver damage and metabolic disorders are associated with elevated concentration of NH3 in the blood.
• In case of CIRRHOSIS (hepatic disease), NH3 rises to toxic levels, consequently: Tremor, blurred, coma and ultimately death.
• The transport of NH3 from the tissue to the liver is done by GLUTAMATE or GLUTAMINE as nontoxic forms.
Biochemistry for nurses: Unit 3
Glutamine Synthase fixes NH3 as Glutamine.
• NH3 is fixed by GLUTAMATE to give GLUTAMINE
• Enzyme = Glutamine Synthase (inside tissue mitochondria)
• That reaction needs ENERGY to work! (hydrolysis of ATP )
Tissues
Biochemistry for nurses: Unit 3
UREA CYCLE • UREA is the major end product of Nitrogen catabolism in human body.
• Synthesis of 1 molecule of UREA requires:
1. 3 molecules of ATP (Energy!)2. 1 molecule of NH4+3. 1 molecule of α- amino group (NH2) of Aspartate
• 5 enzymes catalyse the Urea Cycle in the liver cells:
1. Carbamoyl Phosphate Synthase I2. Ornithine Transcarbamoylase3. Argininosuccinic Acid Synthase4. Argininosuccinase5. Arginase
Biochemistry for nurses: Unit 3
Biochemistry for nurses: Unit 3
Summary of the Urea Cycle
2 NH3 + CO2 + 3 ATP
UREA + 2 ADP + Pi
+ AMP + Pi
Liver
Biochemistry for nurses: Unit 3
Summary of the ammonia elimination
Amino acids
degradation
Amino group
Keto acids« carbon skeletton »
Synthesis of glucosesand lipids
Biochemistry for nurses: Unit 3
Summary of the ammonia elimination
• 1 – 2 % of the body proteins are degraded and renewed daily
• Ammonia (NH3) is highly toxic. • Ammonia (NH3) is converted to Urea
• Glutamine synthase converts NH3 to nontoxic glutamine
• Glutaminase releases NH3 for use in urea synthesis
• NH3, CO2 and the amide nitrogen of aspartate provide the atoms of urea
• Hepatic urea synthesis takes place in part in the mitochondrial matrix and in part in the cytosol.
Biochemistry for nurses: Unit 3
Clinical correlation
Biochemistry for nurses: Unit 3
Metabolic disorders of urea synthesis
• Extremely rare: Dysfunction of enzymes
• Disorders in urea synthesis
Biochemistry for nurses: Unit 3
Metabolic disorders of urea synthesis
• Extremely rare: Dysfunction of enzymes
• Disorders in urea synthesis
[NH3] in blood increases
Biochemistry for nurses: Unit 3
Metabolic disorders of urea synthesis
• Extremely rare: Dysfunction of enzymes
• Disorders in urea synthesis
[NH3] in blood increases
NH3 intoxicationIntoxication is more severe when the urea synthesis is blocked at reactions 1 or 2
Biochemistry for nurses: Unit 3
Metabolic disorders of urea synthesis
• Extremely rare: Dysfunction of enzymes
• Disorders in urea synthesis
[NH3] in blood increases
NH3 intoxicationIntoxication is more severe when the urea synthesis is blocked at reactions 1 or 2
Clinical symptoms:• Vomiting• Avoidance of high protein foods• Irritability• Lethargy• Mental Retardation (Brain damage)
Biochemistry for nurses: Unit 3
Metabolic disorders of urea synthesis
• Extremely rare: Dysfunction of enzymes
• Disorders in urea synthesis
[NH3] in blood increases
NH3 intoxicationIntoxication is more severe when the urea synthesis is blocked at reactions 1 or 2
Clinical Treatments:• Low protein diet ingested• Frequent small meals to
avoid sudden increase in blood of the NH3 levels.
Clinical symptoms:• Vomiting• Avoidance of high protein foods• Irritability• Lethargy• Mental Retardation (Brain damage)
Biochemistry for nurses: Unit 3
Metabolic disorders of urea synthesis
• Extremely rare: Dysfunction of enzymes
• Disorders in urea synthesis
[NH3] in blood increases
NH3 intoxicationIntoxication is more severe when the urea synthesis is blocked at reactions 1 or 2
Clinical Treatments:• Low protein diet ingested• Frequent small meals to
avoid sudden increase in blood of the NH3 levels.
Clinical improvement andminimization of Brain damage.
Clinical symptoms:• Vomiting• Avoidance of high protein foods• Irritability• Lethargy• Mental Retardation (Brain damage)