M.Sc. Medical Biochemistry
M.Sc. Medical Biochemistry
Are most abundantly distributed organic compounds.
70 kg man= protein weight constitute 12 kg
Skeleton and connective tissue contains half
Body protein and other half is intracellular.
The total amount of protein in the body remains
constant (i.e Rate of protein synthesis is constnt)
Is equal to protein degradation.
This process is called as protein turnover.
300 to 400 Gm/day.
Rate turn over
Hours/Days Digestiive Enzymes &
Months/years Collagen.(Structural Proteins)
Proteins rich in Proline, Glutamate, Serine and
threonine are rapidly degraded and short half-lives
Amino acids released by dietary & tissue Protein
Mix with free amino acids of body = Constitutes=100
Glutamate,Glutamine - 50 %
Essential amino acids - 10%.
Remaining Non-Essential Amino Acids.
Proteins rich in Proline,Glutamate,Serine and
Threonine are rapidly degraded and have short half-
AMINO ACID POOL: -Amino acids released by
1.Dietary and 2.Tissue protein.
There is no storage form of amino acids like
Glycogen and Triglycerides.
Excess intake of proteins(Amino acids) are
metabolised then oxidised to provide energy or
converted to glucose or fat.
Amino groups lost as Urea→Excreted.
Body Dietary Synthesis
Protein Protein Non-Essential AA
Body Protein Porphyrins
Purines & Pyrimidins
Glucose CO₂ Fattyacids
Glycogen Ketone Bodies
AMINO ACID POOL
Digestion of Dietary Proteins
Proteins are too large to be absorbed by
intestine and must be hydrolysed to yield
amino acids,which can beabsorbed.
Proteolytic enzymes responsible for degrading
proteins are produced by 3 different organs:
Stomach,Pancreas and Small intestine.
PROTEIN DIGESTION:- Dietary protein-50-100
30-100gm/Day- Endogenous protein from digestive
Dietary proteins are denatured on cooking.
Proteins are degraded by hydrolases which
cleave peptide bonds known as peptidases.
Exopeptidases and endopeptidases.
EXOPEPTIDASES ENDO PEPTIDASES
1.Carboxy peptidases. Aspartate Proteinase
2.Amino peptidases. Eg:- Trypsin
3.Tripeptidyl peptidases. Serine Proteinases
4.Dipeptidyl peptidases. Eg:-Trypsin
5.Dipeptidase Cysteine Proteinases
DIGESTION @ Stomach
HCl , pH=2, Due to HCl, secreted by parietal cells.
Pepsin = Pepsinogen HCl Pepsin.
ABSORPTION :- Occurs in small intestine of infants
immediately after birth. This process is known as
Direct transfer is useful for taking up of maternal
ADULTS:-Direct transfer of intact protein (or) poly
peptide in body elicits Antibody formation(Food
NONTROPICAL SPURE:-Tripeptde digestionof wheat
Glutemate stimulates antibody production.
CELIAC DISEASE in children same phenomena has
Abnormality of protein digestion:-HARTNUP’S
disease is due inability of intestinal absorption of
neutral amino acids.
PROTEIN TURNOVER:-Continuous degradation and
resynthesis occurs in all cellular proteins.
Adults degrade 1-2% of their body protein
75-80% are utilized for protein synthesis.
20-25% for urea.
Proteins are degraded at varying rates.
1.High mean rates of protein degradation occurs in
uterine tissue during pregnacy.
2.During strvation ,skeletal muscle protein
degradation is ↑.
TRANSMINATION is defined as a process in
which amino group is transferred from an Aminoacid
to Ketoacid to form an corresponding Aminoacid that
itself is forming Ketoacid with out liberation of
The enzymes catalyzing the reaction as a group are
known as AMINO TRANSFERASES.
All amino Transferases require coenzyme –
All amino acids ,except LYSINE,THREONINE
participate in Transmination.
The reaction is Cytoplasmic and takes place in
Transminases are induced by Glucocorticoids
which promotes Gluconeogenesis.
Clinical significance:- ↑Levels in plasma indicates
damage to cells rich in these enzymes.
SGPT↑ :- Toxic Hepatisis.
SGOT:- Myocardial infarction,Pulmonary disorders.
Function:- Transmination is useful synthesis of
Non- Essential Aminoacids.
Major oxidative deamination is catalysed.
Glutamate DeHydrogenase (GDH)
It is a mitochondrial enzyme in Liver.
Plants&Microorganisms =D-Aminoacid Oxidase=FAD
All amino acids first transaminated to glutamate and
Then coupling of Transamination & Deamination is
called as Transdeamination.
All amino acids, amino groups are funnelled into
High Protein Diet = High Ammonia formation.
When energy levels are low amino acid degradation
by GDH is High,Provides α-KG for TCA cycle.
1.Enzymes that acts as dehydratases forms
corresponding keto acid and ammonia.
Threonine Deaminase Keto Butyrate +NH₃
Cysteine Pyruvate+NH₃ + H₂S
3.Histidine undergoes non-oxidative deamination
4.Glutamine Glutaminase* Glutamate + NH₃
Aspargine Asparginase* Aspartate + NH₃.
These enzymes have been utilized as Anti-Tumor
*Acts as anti tumor agents
Metabolism of Ammmonia:-
SOURCES OF AMMONIA :-
Amino acids Synthesises Protein,
Protein degraded to Amino acids.
From Liver : a) Transamination
b) Oxidative deamination
From Kidney : Glutaminase reaction
From Intestine : By Bacterial action
From Diet : Amines
From Catabolism : Purines (Adenine)
From Non–oxidative: Deamination : Aminoacids
UTILIZATION OF AMMONIA:-
Glutamate+ Ammonia Glutamine.
Glutamine synthetase- Liver, Brain and Kidney.
Brain :- Major mechanism for removal of
Ammonia is Glutamate formation.
Glutamate may be considered as a major transport
form of NH₃ from tissue to liver.Concentration of
Glutamate in blood is 10 times more than other
3 Important disposal route of ammonia is formation
End product Amino Nitrogen
In mammals is Urea - Ureotelic.
Fishes is Ammonia - Ammonotelic.
Birds & Reptiles is Uric acid - Uricotelic
TRANSPORT OF AMMONIA:-
Ammonia is constantly produed in tissues.
Plasma ammonia - 10-20 μg /dl.
Elevated levels cause symptoms of ammonia
SYMPTOMS:-Tremor, Slurring of speech, Blurring of
vision→Coma and death.
HEREDITARY HYPER AMMONEMIA:-
All inherited deficiencies of UREA CYCLE ENZYMES
result in HYPER AMMONEMIA.
Prevalence is 1 in 30000 individuals.
1.Enzymes of Urea cycle
2.Regulation of Urea cycle
3.Energetics of Urea cycle
4.Clinical significance of blood Urea
5.Disorders of Urea cycle
Urea cycle is also called as Krebs-Henseleit or
Urea synthesized in Liver, released into Blood, cleared
Urea cycle is devided into Five steps.
Two nitrogen atoms of urea are derived from
ammonia and alpha amino group of aspartic
One mol of urea synthesis requires 4 mol of ATP.
Step 1 in Mitochondria:-
CO₂ + Ammonia + 2 ATP Carbamoyl
Carbamoyl phosphate synthase 1(CPS-1)
It is a Mitochondrial enzyme,
Allosteric activator is N-Acetyl Glutamate.
Step 2. Formation of Citrulline
Carbamoyal phosphate +Ornithine
Citrulline + Pi
Ornithine trans carbmoylase is also a Mitochondrial
This step onwards the reactions occurred in
Step3- Formation of Argininosuccinate.
Citrulline + Aspartate + ATP
Argininosuccinate + AMP + PPi
2.Regulation of Urea Cycle :
a) Carbamoyl Phosphate Synthase-1:
Allosteric activator –N-acetylglutamate.
More glutamate, more N-acetylglutamate,
more CPS-1 activity, leads more Urea synthesis.
b) During starvation, Urea cycle enzyme activities are
increased to meet the demands of increased rate of
3 Energetics of Urea cycle:
Carbamoyal phosphate synthase -2ATP
Argininosuccinate synthase -2ATP
Fumarate- Malate- MDH +3ATP
Net Energy expenditure -1ATP
Clinical significance of Blood Urea:
Normal Blood Urea = 15 - 40 mgs %
Normal Urine Urea = 15 - 30 grams/day
Increased Blood Urea levels:
a) High protein diet
b) Increased protein catabolism –starvation
c) Gastro-intestinal haemorrhage.
a) Chronic renal failure
B) Acute glomerulonephritis
a) Renal stone
B) Prostate enlargement
c) Malignant stricture
Decreased Blood Urea Levels:
a) Low protein diet.
b) Liver diseases
c) Water retention.
DISORDERS OF UREA CYCLE:
a) Hyperammonemia - Type I
-Enzyme Defeciency - CPS 1
-Symptoms - Increased blood ammonia (↑ NH₄)
Autosomal recessive .
HYPER AMMONEMIA Type II
Enzyme deficiency –Ornithine transcarbamoylase
↑ NH₃ in Blood; Glutamine ↑ in C.S.F, urine, blood.
Orotic aciduria, Mental retardation.