pharmacy.ppt

1. Biochemistry II
-Amino acid and Protein metabolism
-Molecular genetics
-Vitamin and Minerals
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2. 2
Metabolism of Proteins & Amino acids
Digestion of Proteins
• Proteins must be hydrolyzed first to free amino acids,
which can be absorbed.
• About 95-99% of ingested proteins are digested and
absorbed in GIT.
• No protein digestion in the mouth as saliva lacks any
protease.
Digestion in the stomach
• Gastric parietal cells secrete HCl into the gastric lumen
that makes the stomach highly acidic (pH 1-3).
• Gastric juice contains 2 major digestive enzymes for
protein: pepsin and rennin.
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3. 3
ondensation of the primary –COOH group of an
AA & primary –NH2 group of another AA forms
the peptide bond.
his requires energy and leaves a free amino group
at one end (N-terminus) and a free carboxylic acid
group at the other end (C-terminus) of the product
dipeptide. The bond is rigid.
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4. 4
Functions of proteins
Functions of proteins
roteins are sometimes described as the "workhorses" of the cell because
they do so many things like:
nzymes: kinases, transaminases etc.
torage proteins: myoglobin, ferretin
egulatory proteins: peptide hormones, DNA binding proteins
tructural protein: collagen, proteoglycan
rotective proteins: blood clotting factors, Immunoglobins,
ransport protein: Hemoglobin, plasma lipoproteins
ontractile or motile Proteins: Actin, tubulin
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6. 6
epsin (optimum pH: 1.6-2.5)
ajor protease secreted by the chief cells of the
stomach body into the lumen in an inactive
proenzyme form pepsinogen (362 AAs).
astric HCl activates pepsinogen to pepsin.
oes not hydrolyze keratins, mucoproteins, or basic
proteins.
ndopeptidase i.e. acts on peptide bonds inside the
polypeptide chains.
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7. 7
ennin (optimum pH: 4)
resent in infant's stomach but disappears slowly from
the stomach of adults.
mportant for infants because it coagulates milk in the
stomach to prevent its rapid passage to the intestine.
his gives the baby the satiety and sensation of
fullness.
ecreted as inactive pro-rennin that is activated by
proteolysis and by association with Ca++
ions into
active rennin.
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8. 8
Digestion in intestine
• The partially digested food bolus enters the
duodenum and is met by enzyme rich pancreatic
juice that carries very potent proteolytic enzymes.
Trypsin (optimum pH: 7.9)
• Secreted as trypsinogen and proteolytically activated
into trypsin by enterokinase.
• Calcium enhances the activation process.
• Raw egg white, soybeans and blood contain strong
trypsin inhibitors.
• Endopeptidase & releases smaller peptides and
more free AAs.
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9. 9
C
hymotrypsin (optimum pH 7-8)
ndopeptidase that hydrolyses peptide bonds.
C
arboxypeptidase (optimum pH 7.5)
ydrolyzes the C-terminal AA of polypeptide chains.
E
lastase
ydrolyzes yellow connective tissue fibers (elastin).
C
ollagenase
ydrolyzes white connective tissue fibers (collagen).
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11. 11
Hormones regulating protein digestion
G
astrin:
timulates secretion of pepsinogen and the intrinsic factor from
gastric mucosa.
C
holecystokinin:
ctivates pancreatic proenzyme secretion.
S
ecretin:
timulates secretion of bicarbonate rich pancreatic juice.
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12. 12
Absorption of Amino Acids
- Dietary proteins are almost completely
digested into free amino acids.
- AAs are absorbed from small intestine (in
jejunum) into the portal circulation.
Absorption mechanism:
- active transport (sodium dependent amino acid
co-transproters).
- Facilitated transport (carrier proteins or
symporters)
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13. 13
Hartnup
disease (Neutral amino aciduria)
t is a genetic defect in absorption of neutral amino acids.
he disease is characterized by the inability of renal and intestinal epithelial
cells to absorb tryptophan & other neutral amino acids from the lumen.
lood levels of tryptophan and other neutral amino acids are lower than
normal whereas urine content of neutral amino acids higher than normal.
Symptom
s :
eurological symptoms
ellagra-like skin rash
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14. NITROGEN BALANCEs
Nitrogen balance = nitrogen ingested(N.input) - nitrogen excreted(N.output
(primarily as protein) (primarily as urea)
1. Nitrogen balance (nitrogen equilibrium)
Nitrogen ingested(input)—Nitrogen excreted(out put) = 0 Or NI/NO = 1
It is a steady state
2. Positive nitrogen balance
 when nitrogen input > Nitrogen out put
It is a state of development
 it occurs mostly in well nurished growing children and muscular excersing
individuals
3.Negative nitrogen balance:
 Nitrogen input < nitrogen Output
It is a state of wasting or emaciation
It occurs in persons with HIV/AIDS,TB,cancer ,kwashiorker and
marasmus children

15. Disposal of Nitrogen from Amino Acids
O
verview:
nlike fats and carbohydrates, amino acids are not stored by the body.
herefore, amino acids must be obtained from the diet, synthesized de
novo, or produced from normal protein degradation.
ny amino acids in excess of the biosynthetic needs of the cell are
rapidly degraded.
he first phase of amino acid catabolism involves transamination and
subsequent oxidative deamination, forming ammonia and the
corresponding α-keto acid which is the “carbon skeletons” of amino
acids.
15

16. portion of the free ammonia is excreted in the
urine, but most is used in the synthesis of urea,
which is quantitatively the most important route
for disposing of nitrogen from the body.
n the second phase of amino acid catabolism,
the carbon skeletons of the α-ketoacids are
converted to common intermediates of energy
producing metabolic pathways.
16

17. Overview of Amino Acid Catabolism:
Interorgan Relationships

18. 18
Fig. Fate of amino acid carbons & nitrogen.

19. Amino acid catabolism
Transamination
• The funneling (transfer) of amino groups to glutamate.
• It is the first step in the catabolism of most amino acids
which transfer of their α-amino group to α-ketoglutarate.
• α-Ketoglutarate plays a pivotal (central) role in amino
acid metabolism by accepting the amino groups from
other amino acids, thus becoming glutamate.
• Glutamate produced by transamination can be
oxidatively deaminated, or used as an amino group
donor in the synthesis of nonessential amino acids.
• This transfer of amino groups from one carbon skeleton
to another is catalyzed by a family of enzymes called
aminotransferases (formerly called transaminases).
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20. • The two most important aminotransferase reactions
are catalyzed by alanine aminotransferase (ALT) and
aspartate aminotransferase (AST).
• Transaminases require pyridoxal phosphate (PLP) as
a coenzyme.
Fig: A generalized reaction of transamination
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21. 04/02/25 21

22. Oxidative deamination
n contrast to transamination reactions that transfer amino groups,
oxidative deamination by glutamate dehydrogenase results in the
liberation of the amino group as free ammonia.
hese reactions occur primarily in the liver and kidney.
hey provide α-keto acids that can enter the central pathway of
energy metabolism & ammonia, which is a source of nitrogen in
urea synthesis.
lutamate dehydrogenase (GDH) carries out oxidative deamination
of glutamat into -KGA and liberates NH3 that enters urea cycle.
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23. Fig. Oxidative deamination by GDH
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24. Fig. Combined actions of aminotransferase & GDH reactions.
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25. Transport of ammonia to the liver
• Two mechanisms are available in humans for
the transport of ammonia from the peripheral
tissues to the liver for its ultimate conversion to
urea.
The first, found in most tissues, uses glutamine
synthetase to combine ammonia with glutamate
to form glutamine- a nontoxic transport form of
ammonia. The glutamine is transported in the
blood to the liver where it is cleaved by
glutaminase to produce glutamate and free
ammonia.
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26. 26

27.  The second transport mechanism, used
primarily by muscle, involves transamination of
pyruvate (the end product of aerobic glycolysis)
to form alanine.
• Alanine is transported by the blood to the liver,
where it is converted to pyruvate, again by
transamination (glucose-alaninie cycle).
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28. 28
Fig: The glucose-alanine cycle.

29. Blood Ammonia
H3 is toxic nitrogenous compound
ormal range of NH3 in blood : 10 - 80 g/dl.
apidly removed from circulation by the liver (mainly) and
converted either to glutamate, glutamin or urea.
n liver disorders like alcoholic liver disease or cirrhosis, NH3
not converted into urea and rises in blood, a toxicity
condition known as hyperammonemia.
H3 passes directly to systemic blood through collateral
arteries and exposes brain tissue to the toxic
concentrations.
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30. Sources of blood ammonia
1. From glutamine: the kidneys generate ammonia from
glutamine by the actions of renal glutaminase and
glutamate dehydrogenase. Most of this ammonia is
excreted into the urine as NH4+, which provides an
important mechanism for maintaining the body’s acid-
base balance through the excretion of protons.
2. Intestinal bacterial activity on dietary proteins:
• Putrefaction by the action of bacterial urease, urea
secreted in GI juice, and deamination of other
nitrogenous bases.
• This becomes significant source in constipation,
gastrointestinal hemorrhage and high protein diet.
30

31. t is very important to be prevented in liver diseases;
otherwise ammonia intoxication would be worsened.
ntestinal antiseptic antibiotics and enema are very
beneficial in such cases.
.From amines: amines obtained from the diet, and
monoamines that serve as hormones or
neurotransmitters, give rise to ammonia by the action of
amine oxidase.
. From purines and pyrimidines: in the catabolism of
purines and pyrimidines, amino groups attached to the
rings are released as ammonia.
31

32. atabolic fate of ammonia (direct excretion):
H3 is excreted directly into the urine in the form of NH4
+
after conjugation with H+
in exchange with Na+
.
his is an important acid-base balancing mechanism for
removal of extra-acid from the body, particularly in
acidosis.
nabolic fates of ammonia:
ynthesis of urea, non-essential amino acids, purines,
pyrimidines, porphyrins, sugaramines and glutamine
synthesis (glutamine cycle). 32

33. Hyperammonemia (ammonia intoxication)
W
hy NH3 is toxic to brain?
epletion of -KGA of Krebs' cycle in brain leading to
energy failure.
epletion of brain glutamate leading to deficiency of GABA
(an inhibitory neurotransmitter) that is a decarboxylation
product of glutamate.
ncreased entrance of tryptophan to the brain (in exchange
with glutamin) leading to increased level of serotonin
(stimulatory neurotransmitter) synthesized from tryptophan.
33

34. Urea Cycle
• A five reaction cyclic cascade that utilizes two amino
groups and a CO2 to synthesize urea, the nitrogenous
waste of our body.
• Major pathway of N excretion.
• 80-90% of the protein N released as NH3 is excreted
in man as urea.
• Urea is synthesized in the liver, diffuses freely into
the blood and is cleared through the kidneys.
• Liver is the only tissue that synthesizes urea from
NH3 and CO2.
• The first two steps occur in mitochondria whereas
the remaining occurs in the cytosol.
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36. he changes in demand for urea cycle activity are
met in the long term
by regulation of the rates of synthesis of the
four urea-cycle enzymes specialy carbamoyl
phosphate synthetase I in the liver
ll the five enzymes are synthesized at higher rates in
starving animals and in animals on a very high protein
diet 04/02/25 36

37. Metabolic disorders of the urea cycle
The disorder can be acquired or hereditary
1. hereditary
A) Deficiency of each of the five enzymes
concerned in the urea cycle may occur,
resulting in the respective metabolic disorder.
 All enzyme deficiency cause ammonia
intoxication and have similar symptoms like
vomiting,irritability,lethargy, ataxia, and
mental retardation

38. 2.acquired
n this case the urea cycle enzymes are
normal
the problem may be in the liver and kidney
or any other causes

39. Treatment Strategy for urea cylce disorder
(hyperammonimia)
limiting dietary protein to minimize
rugs Administration of benzoate, phenylbutyrate,
or phenylacetate can also be used to manage
the condition.
ialysis.
iver transplantation

40. emoglobin degradation
fter approximately 120 days in the circulation, RBCs are taken
up and degraded by the RES, particularly in the liver and
spleen.
pproximately 85% of heme destined for degradation comes
from RBCs, and 15% is from turnover of immature RBCs and
cytochromes from extra-erythroid tissues.
n the reticulo-endothilial system, hemoglobin is split to heme
and globin.
lobin may be reused either as such or degraded to amino
acids which may be recycled.
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41. emoglobin degradation
fter approximately 120 days in the circulation, RBCs are taken
up and degraded by the RES, particularly in the liver and
spleen.
pproximately 85% of heme destined for degradation comes
from RBCs, and 15% is from turnover of immature RBCs and
cytochromes from extra-erythroid tissues.
n the reticulo-endothilial system, hemoglobin is split to heme
and globin.
lobin may be reused either as such or degraded to amino
acids which may be recycled.
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42. eme catabolism
ormation of bilirubin
eme is oxidized and cleaved to produce carbon monoxide and
biliverdin (green pigment) by microsomal heme oxygenase
system of the reticuloendothelial cells.
iliverdin is reduced, forming the red-orange bilirubin.
ilirubin and its derivatives are collectively termed bile pigments.
he major source of this bile pigment is hemoglobin
(cytochromes and myoglobin other sources).
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43. 2. Uptake of bilirubin by the liver
• Bilirubin is only slightly soluble in plasma and,
therefore, is transported to the liver by binding
non-covalently to albumin.
• Bilirubin dissociates from the carrier albumin
molecule and enters a hepatocyte, where it
binds to intracellular proteins, particularly the
protein ligandin.
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44. 3.
Formation of bilirubin diglucuronide
n the hepatocyte, the solubility of bilirubin is increased by the
addition of two molecules of glucuronic acid (conjugation).
he reaction is catalyzed by microsomal bilirubin
glucuronyltransferase.
4.
Secretion of bilirubin into bile
ilirubin diglucuronide (conjugated bilirubin) is actively transported
into the bile canaliculi and then into the bile.
his energy-dependent rate-limiting step is susceptible to
impairment in liver disease.
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45. 5.
Formation of urobilinogens in the intestine
ilirubin diglucuronide is hydrolyzed and reduced by bacteria in the gut to
yield urobilinogen, a colorless compound.
ost of the urobilinogen is oxidized by intestinal bacteria to stercobilin,
which gives feces the characteristic brown color.
owever, some of the urobilinogen is reabsorbed from the gut and enters
the portal blood.
portion of this urobilinogen enters in the enterohepatic urobilinogen cycle
in which it is taken up by the liver, and then resecreted into the bile.
he remainder of the urobilinogen is transported by the blood to the kidney,
where it is converted to yellow urobilin and excreted, giving urine its
characteristic color.
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46. Bilirubin Production
Heme
(250 to 400 mg/day)
Heme oxygenase
Biliverdin reductase
Hemoglobin
(70 to 80%)
Erythroid cells
Heme proteins
myoglobin, cytochromes
(20 to 25%)
Biliverdin
Bilirubin
NADPH + H+
NADP+
3 [O]
Fe3+
+ CO
apoferritin
ferritin
indirect
unconjugated
pre-hepatic
albumin

47. Fig. Overview of heme degradation.
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48. J
aundice
t is most common known disease of bilirubin metabolism in
which skin and sclera of eye acquires yellow color due to
excessive bilirubin in blood.
n jaundice the plasma bilirubin level is high
(hyperbilirubinemia).
ence excess bilirubin diffuses into tissues and turns them yellow.
hus the characteristic signs of jaundice are hyperbilirubinemia
and yellow colored skin and sclera.
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49. What’s the cause of jaundice?
1-Pre-hepatic jaundice
Increased production of bilirubin by hemolysis or blood disease:
(hemolytic jaundice}
•Increase in blood indirect bilirubin
•Called pre-hepatic jaundice
•Stool color remains normal.
2- Hepatocellular jaundice(intrahepatic juandice)
defective uptake, reduced conjugation
or - impaired intracellular transport
Caused by liver damage or disease.
•Can result in hepatocyte destruction and therefore
unconjugated hyperbilirubinaemia
•Stool color turns gray.

50. 3- Obstructive jaundice(Posthepatic jaundice
s caused by obstruction of the biliary tree.
he plasma bilrubin is conjugated, and other biliary metabolites,
such as bile acids, accumulate in the plasma.
he clinical features are pale-colored stools
nd dark urine
n complete obstruction, urobilinogen/urobilin is absent from urine,
as there can be no intestinal conversion of bilirubin to
urobilinogen/urobilin, and hence no renal excretion of reabsorbed
urobilinogen/urobilin.

51. Table 2- Genetic Disorders of Bilirubin Metabolism
Condition Defect Bilirubin
Clinical
Findings
Crigler-
Najjar
syndrome
severely defective
UDP-
glucuronyltransferase
Unconjugated
bilirubin 
Profound
jaundice
Gilberts
syndrome
reduced activity of
UDP-
glucuronyltransferase
Unconjugated
bilirubin 
Very mild
jaundice during
illnesses
Dubin-
Johnson
syndrome
abnormal transport of
conjugated bilirubin
into the biliary system
Conjugated
bilirubin 
Moderate
jaundice

52. What is neonatal jaundice (jaundice in newborn infants)?
eonatal jaundice is jaundice that begins within the first few
days after birth.
aundice that is present at the time of birth suggests a more
serious cause of the jaundice.)
n fact, bilirubin levels in the blood become elevated in almost
all infants during the first few days following birth,
jaundice occurs in more than half of newborns.
For all but a few infants, the elevation and jaundice
represents a normal physiological phenomenon and does not
cause problems.

53. Cause of neonatal jaundice
igh turnover of RBC breakdown (physiological juandice)
he liver in a newborn infant is not significantly mature, and
its ability to process and eliminate bilirubin is limited
reast-milk jaundice,
ertain newborn digestive system disorders, infections and
genetic disorders also can contribute to jaundice
emolytic disease of the newborn

54. Treatment & Therapeutic Considerations
* A)
Treating the underlying causes
B)
PHOTOTHERAPY**
hrough absorption of the wavelengths at the blue end of the spectrum (blue, green and white
light), bilirubin is converted into water-soluble photoisomers. This transformation enhances the
molecule’s excretion into bile without conjugation.
C)
PHENOBARBITAL
his drug is not approved by FDA for use in neither adult nor pediatric hyperbilirubinemia
patients, due to possibility of significant systemic side-effects.
xact pathway is not known, but it is believed to act as an inducing agent on UDP-
glucuronosyltransferase, thereby improving conjugation of bilirubin and its excretion.
D)
ALBUMIN
25% infusion can be used in treating hyperbilirubinemia (esp. due to hemolytic disease).
t is used in conjunction with exchange transfusion to bind bilirubin, enhancing its removal.
E)
PERCUTANEOUS TRANSHEPATIC CHOLANGIOGRAPHY**
llows extraction of stones and thus removal of the source of obstruction when present.

55. ADVERSE THERAPEUTIC EFFECTS
ADVERSE THERAPEUTIC EFFECTS
 Flavopiridol
Flavopiridol –
– can induce hyperbilirubinemia. It shares
can induce hyperbilirubinemia. It shares
the glucuronidation pathway that is involved in bilirubin
the glucuronidation pathway that is involved in bilirubin
conjugation, effectively reducing the amount of
conjugation, effectively reducing the amount of
bilirubin that can be processed by the hepatic cells at
bilirubin that can be processed by the hepatic cells at
any given time.
any given time.
 Novobiocin
Novobiocin –
– inhibits the UDP-glucuronosyltransferase
inhibits the UDP-glucuronosyltransferase
activity, leading to hyperbilirubinemia.
activity, leading to hyperbilirubinemia.
 Valspodar
Valspodar –
– causes an increase in bilirubin levels by P-
causes an increase in bilirubin levels by P-
glycoproteins in the biliary canaliculi, thus interfering
glycoproteins in the biliary canaliculi, thus interfering
with bilirubin transport.
with bilirubin transport.