ENZYMES

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ENZYMES

• M.Prasad Naidu
• MSc Medical Biochemistry, Ph.D,.

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Classification of enzymes
Based on the type of reaction enzymes can be
classified into SIX MAJOR TYPES

• Oxidoreductases- lactate dehydrogenase
• Transferases- glucokinase
• Hydrolases- chymotrypsin, G6Pase
• Lyases- fumarase
• Isomerases- phosphoglucoisomerase
• Ligases- Acyl CoA synthetase

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OXIDOREDUCTASE
Transfer of electrons (Hydride ions or H atoms)
There are several subclasses
1) Dehydrogenases 2) Oxidases 3) Oxygenases
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Dehydrogenases
Remove electrons and/or hydrogen atoms
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Oxygenases
Catalyze incorporation of oxygen into a substrate

Hydroxylation of Progesterone by a Monooxygenase
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TRANSFERASES
Transfer functional groups in group transfer
reactions
Types of transferases
1) Amino transferases 2) Kinases 3) Glycosyl
transferases
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Amino Transferases (or Transaminase)
Transfer an amino group from one amino acid to a
new keto acid
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Kinases
Catalyze transfer of the phosphoryl group
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Glycosyl Transferases
Transfer an activated glycosyl residue to a
glycogen primer. This is a key enzyme in
glycogen synthesis
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HYDROLASES
Hydrolysis reactions
The generalized reaction involves hydrolytic
cleavage of C-O, C-N, O-P, and C-S bonds
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Peptidase
Cleavage of a peptide bond by peptidases
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LYASES
Addition or removal of elements of water,
ammonia, or carbon dioxide
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Decarboxylases
Removal of an element of CO2 from a- and b-keto
acids or amino acids
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Pyruvate Decarboxylase
The substrates bicarbonate and pyruvate are
ligated to form a four-carbon (C4) oxaloacetate
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Dehydratases
Fumarase reversibly converts fumarate to malate.
It removes H2O in a dehydration reaction
converting malate to fumarate
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Isomerases
Transfer of groups within molecules to yield
isomeric form
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Epimerases
Isomerases that catalyze inversion at asymmetric
carbon atoms
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LIGASES
Involved in synthetic reactions where two
molecules are joined at the expense of a
high-energy phosphate bond of ATP
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6.Ligases

• Biotin
• Acetyl CoA CO2 Malonyl CoA
• ATP ADP Pi
• Enzyme is Acetyl CoA carboxylase or Acetyl
  CoA-CO2 ligase (systematic) code number
  EC.6.4.1.2ese enzymes link two substrates
  together, usually.

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Significance of Km

• km indicates the affinity of enzyme to the
  substrate
• Smaller the km larger the affinity
• Larger the km smaller the affinity

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• Substrate conc affects reaction velocity (rate)
• As substrate concentration is increased, Initial
  velocity vi, increases until it reaches maximum
  Vmax.
• further increase in substrate concentration does
  not increase velocity the enzyme is said to be
  saturated.
• Note that the shape of the graphic curve
  relating to catalytic activity and substrate
  concentration is hyperbolic

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• Michaelis menten equation illustrates in
  mathematical terms the relationship between
  initial reaction velocity , vi, and substrate
  concentration.
• Km Michaelis constant
• Vmax maximal velocity
• Vi initial velocity
• s substrate concentration
• Vmax s
• Vi
• Km s

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• Km value or Michaelis menten constant is
  defined as substrate concentration (expressed in
  moles / liter) to produce half maximal velocity
  in an enzyme catalysed reaction at a particular
  enzyme concentration.
• It indicates that 50 of enzyme molecules are
  bound with the substrate molecules.
• Its a characteristic of an enzyme or signature
  of an enzyme.
• Lower the Km value Higher the affinity of the
  enzyme for substrate.
• Higher the Km value, the affinity of the enzyme
  for the substrate is low.

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• Hexokinase
• Glucose Glucose-6-Phosphate
• ATP ADP
• Glucokinase
• HK Km value 10-2 mmol / L
• GK Km value 20 mmol / L

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Enzyme Patterns (Enzyme profiles) in diseses

• 1.Hepatic diseases
• 1.Alanine amino transferase (ALT)
• Marked increase in parenchymal liver disease
• 2. Alkaline phsophatase (ALP)
• Marked increase in obstructive liver disease
• 3.Nucleotide phsophatase (NTP)
• Elevated in liver dysfunction with cholestasis
• 4. Gamma glutamyl transferase (GGT)
• Increase in obstructive and alcoholic liver
  disease

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• II.Myocardial Infarction
• 1.Cratine Kinase (CK MB)
• First enzyme to rise following infarction,
  CK-MB isoenzyme
• is specific.
• 2.Aspartate amino transferase (AST)
• Rises after the rise in CK and returns to
  normal in 4-5 days
• 3.Lactate dehydrogenase (LDH)
• Last enzyme to rise. LDH-1 becomes more than 2
  (Flipped
• pattern)

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• Enzyme pattern in Myocardial infraction

AST
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Normal pattern of LDH in serum
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Flipped pattern of LDH in MI
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• III.Muscle disease
• 1.Creatine Kinase (CK-MM)
• Marked increase in muscle disease. CK-MM
  fraction is elevated
• 2. Aspartate amino transferase (AST)
• Shows an increase in different types of muscle
  diseas not specific
• 3. Aldolase
• Earliest enzyme to rise. But not specific

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• IV. Bone diseases
• 1.Alkanine phosphatase (ALP)
• Marked elevationin osteoblastic bone activity
  as in rickets. Heat labile bone isoenzyme is
  elevated. Also in Pagets disease.
• V.Prostate cancer
• 1.Prostate specific antigen (PSA)
• Marker for prostate cancer. Mild increase in
  benign prostate enlargement.
• 2. Acid phosphatase (ACP)
• Marker for prostate cancer . Metastatic bone
  disease especially from a primary from prostate.

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THANK YOU