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Isoenzymes & Clinical Enzymology
Gandham.Rajeev
Plasma Enzymes
Sources of plasma enzymes: Two types
Plasma derived
Cell derived
Plasma derived enzymes:
These enzymes act on substrates in plasma &
their activity is higher in plasma than cells.
E.g. coagulation enzymes.
Cell derived enzymes
These enzymes have a high activity in cells & overflow
into the plasma.
Further subdivided into
Secretory enzymes:
These are mainly derived from digestive glands &
function in extracellular space.
Metabolic enzymes:
These are concerned with intermediary metabolism &
function in the cells
Classification of Plasma enzymes
Enzymes present in plasma are grouped into
functional & non-functional enzymes
Functional enzymes Non-functional enzymes
Pseudocholinesterase Aspartate transaminase
Lipoprotein lipase Creatinine kinase
Ceruloplasmin Amylase
Blood coagulation enzymes Alkaline phosphatase
Functional enzymes
Few enzymes in plasma are functionally important & they are
involved in blood clotting, lipoprotein metabolism & drug
metabolism.
Synthesized in liver & released into plasma.
E.g. Pseudocholinesterase, Lipoprotein lipase, Ceruloplasmin,
Blood coagulation enzymes
Clinical significance:
These are present in higher concentrations in plasma than cells.
These are clinically significant when the serum level is
decreased below the reference range.
Non-functional enzymes
Most of the enzymes present in plasma serve no function in the
plasma.
Non-functional enzymes are derived from cells of organs &
tissues.
Present in high concentrations within cells
E.g. AST, ALT, LDH,CK,ALP, amylase
Clinical significance:
Non-functional enzymes in plasma are present in low
concentrations.
These are clinically important when the serum level is increased
above the reference range.
Causes for increased level of non-functional enzymes in plasma
Increased level of non-functional enzymes in plasma
include
Hypoxic or infective insults
Disease states of tissues
Excessive synthesis or induction of enzymes by cells with
overflow into plasma
Vigorous exercise
Decreased renal clearance
Isoenzymes
Isoenzymes or isozymes are multiple forms of same
enzyme that catalyze the same chemical reaction
Different chemical and physical properties:
Electrophoretic mobility
Kinetic properties
Amino acid sequence
Amino acid composition
Lactate Dehydrogenase
Lactate dehydrogenase (LDH) is an enzyme present in
a wide variety of organisms
EC 1 = oxidoreductase.
EC 1.1 = acting on the CH-OH group of the donor.
EC 1.1.1 = With NAD or NADP as acceptor.
EC 1.1.1.27 = L-lactate dehydrogenase.
Molecular weight- 32 kD & it is tetramer
M (A) -muscle –chromosome 11(basic)
H (B) -heart – chromosome 12(acidic)
Lactate dehydrogenase, reversibly converts lactate to
pyruvate, in different tissues.
LDH consists of 5 iso-enzymes –
LDH1,LDH2,LDH3,LDH4 & LDH5
These isoenzymes are separated by cellulose acetate
electrophoresis at pH 8.6
Normal values:
Serum -100 -200 U/L
CSF - 7 -30 U/L
Urine - 40 -100 U/L
LDH reaction
LDH isoforms
LDH isoforms
Isoenzyme name
Composition Electrophoretic migration
Present in Elevated in
LDH 1Heat resistant ( H4) Fastest moving
Myocardium, RBC, kidney
myocardial infarction
LDH2Heat resistant (H3M1)
Myocardium, RBC, kidney
Kidney disease,megaloblastic anemia
LDH3 (H2M2) brain Leukemia, malignancy
LDH4Heat labile
(H1M3) Lung, spleen Pulmonary infarction
LDH5Heat labileInhibited by
urea
(M4) Slowest moving Skeletal muscle, Liver
Skeletal muscle and liver diseases
Clinical significance of LDH
In normal serum, LDH2 (H3M) predominant
isoenzyme & LDH5 is rarely seen.
In myocardial infarction, LDH1(H4) levels are greater
than LDH2.
Megaloblastic anemia (50 times upper limit of LDH 1
and LDH 2)
Muscular dystrophy, LDH5 (M4) is increased.
Toxic hepatitis with jaundice (10 times more LDH5)
Renal disease- tubular necrosis or pyelonephritis, pulmonary
embolism LDH 3 (massive destruction of platelets)
Total LDH is increased in neoplastic diseases.
LDH5 is increased in breast cancer, malignancies of CNS,
prostatic carcinoma.
In leukaemias, LDH2 & LDH3 levels are increased.
In malignant tumors of testis & ovaries, LDH2, LDH3 & LDH
5 levels are increased.
In CSF:
Bacterial meningitis – LDH4 and LDH5
Viral meningitis - LDH1
Metastatic tumors - LDH5
Neonatal cases of intracranial haemorrhage
associated with seizures and hydrocephalus
Creatinine phosphokinase (CPK)
It catalyses creatine to creatine phosphate. Normal serum value: 15-100 U/L for males & 10-80 U/L for females.
CPK consists of 3 isoenzymes.
Each isoenzyme of CK is a dimer;
Molecular weight of 40 kD.
The subunits are called B for brain (chromosome -14)
& M for muscle (chromosome -19)
Creatine Phosphokinase (CPK)
It is an important enzyme in energy
metabolism.
Immediate source of ATP in contracting muscle.
Three Iso-enzymes are separated by electrophoresis.
CPK-1 (also called CPK-BB) is found mostly in the brain &
lungs.
CPK-2 (also called CPK-MB) is found mostly in the heart.
CPK-3 (also called CPK-MM) is found mostly in skeletal
muscle.
Creatine phosphokinase isoenzymes
ISOENZYMES
SUB-UNIT TISSUE % IN SERUM
CK1 Fast moving
BB Brain 1
CK2 2% of total
MB Heart 5
CK3 Slow moving MM
Skeletal muscle 80
Clinical significance of CK
CPK & heart attack:
CPK2 isoenzymes is very small, (2% of total CPK
activity) & undetectable in plasma.
In myocardial infarction (MI), CPK2 levels are
increased within 4 hrs, then falls rapidly.
Total CPK level is elevated upto 20-folds in MI.
CPK & Muscle diseases
CPK level is elevated in muscular dystrophy (500-
1500U/L)
CPK level is highly elevated in crush injury, fracture &
acute cerebrovascular accidents.
Estimation of total CPK is employed in muscular
dystrophies & CPK-MB isoenzyme is estimated in
myocardial infarction.
Atypical forms of CK
Two atypical isoforms.
1. Macro-CK (CK-macro)
Formation:
Formed by aggregation CK-MB with IgG, sometimes IgA.
Also formed by complexing CK-MM with lipoproteins.
Electrophoretically migrates between CK-MB & CK-MM.
Occurs frequently in women above 50 years.
CK-Mi (Mitochondrial CK-Isoenzyme)
Formation:
It is present bound to the exterior surface of inner
mitochondrial membrane of muscle, liver & brain.
It exist in dimeric form & oligomeric aggregates &
molecular weight 35,000
Electrophoretically, migrates towards cathode & is
behind CK-MM band.
It is not present in normal serum.
Clinical significance
It is present in serum when there is extensive tissue
damage causing breakdown of mitochondrial & cell wall.
Its presence in serum indicates cellular damage, seen in
malignancies.
Alkaline Phosphatase (ALP)
ALP is nonspecific enzyme. It hydrolyses aliphatic, aromatic or heterocyclic
compounds. Optimum pH-9 &10 & it is activated by Mg2+ &Mn. Zn is a constituent of ALP. It is produced by osteoblasts of bone, and is associated
with the calcification process. It is localised in cell membranes -ecto-enzyme. It is associated with transport mechanisms in liver,
kidney & intestinal mucosa.
Normal range-40-125 U/L.
In children, Increased levels are seen, due to increased
osteoblastic activity.
Moderate (2-3) increase in ALP level is seen in hepatic diseases
such as infective hepatitis, alcoholic hepatitis or hepatocellular
carcinoma.
Very high levels of ALP (10-12 times of upper limit) may be
noticed in extrahepatic obstruction (obstructive jaundice) caused
by gallstones or by pressure on bile duct by carcinoma of head of
pancreas
Intrahepatic cholestasis may be due to virus (infective
hepatitis) or by drugs (chlorpromazine).
ALP is produced by epithelial cells of biliary canaliculi &
obstruction of bile with consequent irritation of epithelial
cells leads to secretion of ALP into serum.
Drastically high levels of ALP (10-25 times of upper limit) are
seen in bone diseases where osteoblastic activity is
enhanced such as Paget's disease (osteitis deformatis),
rickets, osteomalacia, osteoblastoma, metastatic carcinoma
of bone and hyperparathyroidism.
Isoenzymes of ALP
Alpha-1 ALP moves in alpha-1 position, it is synthesized by
epithelial cells of biliary canaliculi.
It is about 10% of total activity and is increased in obstructive
jaundice.
Alpha-2 heat labile ALP is stable at 56oC; but loses its activity
when kept at 65oC for 30 minutes.
It is produced by hepatic cells.
This liver iso-enzyme forms about 25% of total ALP.
Alpha-2 heat stable ALP will not be destroyed at
65oC, but is inhibited by phenylalanine.
It is of placental origin, which is found in blood in
normal pregnancy.
An isoenzyme closely resembling the placental form
is characteristically seen in circulation in about 15%
cases of carcinoma of lung, liver and gut and named
as Regan iso-enzyme or carcinoplacental iso-
enzyme.
Normal level is only 1% of the total ALP.
Pre-beta ALP is of bone origin and elevated levels are seen in bone
diseases.
This is heat labile (destroyed at 56°C, 10 min).
This constitutes about 50% of normal ALP activity.
Heat labile bone iso-enzyme of alkaline phosphatase (BAP) is a marker of
bone disease.
Gamma-ALP is inhibited by phenylalanine and originates from intestinal
cells.
It is increased in ulcerative colitis.
About 10% of plasma ALP are of intestinal origin.
The leukocyte alkaline phosphatase (LAP) is significantly decreased in
chronic myeloid leukemia & it is increased in lymphomas.
Clinical significance of enzymes & iso-enzymes in different disease
conditions
Clinical significance of enzymes & isoenzymes
Serum enzymes in heart diseases/cardiac biomarkers
Biomarker is useful in detecting dysfunction of an organ.
Cardiac biomarkers are used to detect cardiac diseases, include
Any chest pain
Unstable angina
Suspicious ECG changes
History suggestive of myocardial infarction
Following surgical coronary revascularization
Patients with hypotension and dyspnea
Markers for cardiac diseases
Creatine kinase (CK-MB)
Cardiac troponin I (CTI) & Cardiac troponin (CTT)
CTI & CTT are not true enzymes
Brain natriuretic peptide (BNP)
BNP is a reliable marker of ventricular function
Lactate dehydrogenase
Aspartate transferase
Creatinine phosphokinase (CPK)
It catalyses creatine to creatine phosphate. Normal serum value 15-100 U/L for males & 10-80 U/L for females.
CPK consists of 3 isoenzymes.
Each isoenzyme of CK is a dimer;
Molecular weight of 40 kD.
The subunits are called B for brain (chromosome -14)
& M for muscle (chromosome -19)
Creatine Phosphokinase (CPK)
It is an important enzyme in energy
metabolism.
Immediate source of ATP in contracting muscle.
Three Iso-enzymes are separated by electrophoresis.
CPK-1 (also called CPK-BB) is found mostly in the brain &
lungs.
CPK-2 (also called CPK-MB) is found mostly in the heart.
CPK-3 (also called CPK-MM) is found mostly in skeletal
muscle.
Creatine phosphokinase isoenzymes
ISOENZYMES
SUB-UNIT TISSUE % IN SERUM
CK1 Fast moving
BB Brain 1
CK2 2% of total
MB Heart 5
CK3 Slow moving MM
Skeletal muscle 80
Clinical significance of CK
CPK & heart attack:
CPK2 isoenzymes is very small, (2% of total CPK
activity) & undectable in plasma.
In myocardial infarction (MI), CPK2 levels are
increased within 4 hrs, then falls rapidly.
Total CPK level is elevated upto 20-folds in MI.
CPK & Muscle diseases
CPK level is elevated in muscular dystrophy (500-
1500U/L)
CPK level is highly elevated in crush injury, fracture &
acute cerebrovascular accidents.
Estimation of total CPK is employed in muscular
dystrophies & CPK-MB isoenzyme is estimated in
myocardial infarction.
Cardiac troponins (CTI/CTT)
They are not enzymes.
Troponins are now accepted as reliable markers for MI
Cardiac troponins have become one of the main tests in early
detection of an ischemic episode and in monitoring the
patient
The troponin complex consists of 3 components
Troponin C (calcium binding subunit),
Troponin I (actomyosin ATPase inhibitory subunit) &
Troponin T (tropomyosin binding subunit)
Troponin I (TnI) is encoded by 3 different genes, giving rise to 3
isoforms; the "slow" and "fast" moving forms are skeletal
variety.
Cardiac isoform is specific for cardiac muscle; the amino acid
sequence is different in skeletal muscle isoform.
Cardiac isoform of CTnT and CTnI are mainly (95%) located in
myofibrils and the remaining 5% is cytoplasmic.
They are identified and quantitated by immunological (ELISA or
immuno turbidimetric) reactions.
Troponins are seen in skeletal and cardiac muscles, but not in
smooth muscles.
Troponin I is released into the blood within 4 hours after the onset of
symptoms of myocardial ischemia; peaks at 14-24 hours and remains
elevated for 3-5 days post-infarction.
CTI is very useful as a marker at any time interval after the heart
attack.
It is not increased in muscle injury; whereas CK2 may be elevated in
some muscle injury.
The initial increase is due to liberation of the cytoplasmic fraction and
sustained elevation is due to the release from myofibrils.
Serum level of Troponin T (TnT) increases within 6 hrs of myocardial
infarction, peaks at 72 hours and then remains elevated up to 7-14
days.
Brain Natriuretic Peptide (BNP)
The natriuretic peptide family consists of three
peptides:
Atrial natriuretic peptide (ANP),
Brain natriuretic peptide (BNP)
C-type natriuretic peptide (CNP).
The clinical significance of CNP is not clear.
ANP is produced primarily in the cardiac atria.
BNP is present in human brain, but more in the cardiac
ventricles.
Human pro–BNP contains 108 amino acids.
It is cleaved by enzymes within cardiac myocytes into the
active C-terminal BNP (32 amino acids) and an inactive
peptide (proBNP 1–76).
Both are seen in circulation.
The active BNP is secreted by the ventricles of the heart
in response to excessive stretching of heart muscle cells
(cardiomyocytes).
Clinical Significance
Patients with congestive heart failure have high plasma
concentrations of ANP and BNP.
The concentrations are correlated with the extent of
ventricular dysfunction.
High concentrations of BNP predict poor long-term survival.
In breathlessness, BNP test helps in the differentiation of the
cause as heart failure or obstructive lung disease.
The best marker of ventricular dysfunction is pro-BNP.
Lactate Dehydrogenase
Lactate dehydrogenase (LDH) is an enzyme present in
a wide variety of organisms, including plants and
animals"
EC 1 = oxidoreductase.
EC 1.1 = acting on the CH-OH group of the donor.
EC 1.1.1 = With NAD or NADP as acceptor.
EC 1.1.1.27 = L-lactate dehydrogenase.
Molecular weight- 32 kD & it is tetramer
M (A) -muscle –chromosome 11(basic)
H (B) -heart – chromosome 12(acidic)
Lactate dehydrogenase, reversibly converts lactate to
pyruvate, in different tissues.
LDH consists of 5 iso-enzymes –
LDH1,LDH2,LDH3,LDH4 & LDH5
These isoenzymes are separated by cellulose acetate
electrophoresis at pH 8.6
Normal values:
Serum -100 -200 U/L
CSF - 7 -30 U/L
Urine - 40 -100 U/L
LDH reaction
LDH isoforms
LDH isoforms
Isoenzyme name
Composition Electrophoretic migration
Present in Elevated in
LDH 1Heat resistant ( H4) Fastest moving
Myocardium, RBC, kidney
myocardial infarction
LDH2Heat resistant (H3M1)
Myocardium, RBC, kidney
Kidney disease,megaloblastic anemia
LDH3 (H2M2) brain Leukemia, malignancy
LDH4Heat labile
(H1M3) Lung, spleen Pulmonary infarction
LDH5Heat labileInhibited by
urea
(M4) Slowest moving Skeletal muscle, Liver
Skeletal muscle and liver diseases
Clinical significance of LDH
In normal serum, LDH2 (H3M) predominant
isoenzyme & LDH5 is rarely seen.
In myocardial infarction, LDH1(H4) levels are greater
than LDH2.
Megaloblastic anemia (50 times upper limit of LDH 1
and LDH 2)
Muscular dystrophy, LDH5 (M4) is increased.
Toxic hepatitis with jaundice (10 times more LDH5)
Renal disease- tubular necrosis or pyelonephritis
Pulmonary embolism LDH 3 (massive destruction
of platelets)
Total LDH is increased in neoplastic diseases.
LDH5 is increased in breast cancer, malignancies
of CNS, prostatic carcinoma.
In leukaemias, LDH2 & LDH3 levels are increased.
In malignant tumors of testis & ovaries, LDH2,
LDH3 & LDH 5 levels are increased.
In CSF:
Bacterial meningitis – LDH4 and LDH5
Viral meningitis - LDH1
Metastatic tumors - LDH5
Neonatal cases of intracranial haemorrhage
associated with seizures and hydrocephalus
Aspartate aminotransferase (AST)
It was also called as serum glutamate oxaloacetate transaminase
(SGOT).
AST needs pyridoxal phosphate (vitamin B6) as co-enzyme.
Normal serum level: 8 to 20 U/L.
It is a marker of liver injury and shows moderate to drastic increase
in parenchymal liver diseases like hepatitis and malignancies of liver.
AST was used as a marker of myocardial ischemia in olden days.
The level is significantly elevated in myocardial infarction.
But troponins have replaced AST as a diagnostic marker in IHD
Alanine aminotransferase (AST)
It was called as serum glutamate pyruvate transaminase (SGPT) The enzyme needs pyridoxal phosphate as coenzyme.Normal serum level: male is 13-35 U/L & female is 10-30 U/L.Very high values (300 to 1000 U/L) are seen in acute hepatitis,
either toxic or viral in origin.Both ALT and AST levels are increased in liver disease, but ALT >
AST. Rise in ALT levels may be noticed several days before clinical signs
such as jaundice are manifested.Moderate increase (50 to 100 U/L) of ALT may be seen in chronic
liver diseases such as cirrhosis, hepatitis C and non-alcoholic steatohepatitis (NASH).
Alkaline Phosphatase (ALP)
ALP is nonspecific enzyme.
It hydrolyses aliphatic, aromatic or heterocyclic compounds.
Optimum pH-9 &10 & it is activated by Mg2+ &Mn
Zn is a constituent of ALP.
It is produced by osteoblasts of bone and is associated with the
calcification process.
It is localised in cell membranes -ecto-enzyme
Associated with transport mechanisms in liver, kidney & intestinal
mucosa.
Normal range-40-125 U/L.
In children, Increased levels are seen, due to increased
osteoblastic activity.
Moderate (2-3) increase in ALP level is seen in hepatic diseases
such as infective hepatitis, alcoholic hepatitis or hepatocellular
carcinoma.
Very high levels of ALP (10-12 times of upper limit) may be
noticed in extrahepatic obstruction (obstructive jaundice)
caused by gallstones or by pressure on bile duct by carcinoma
of head of pancreas
Intrahepatic cholestasis may be due to virus (infective hepatitis)
or by drugs (chlorpromazine).
ALP is produced by epithelial cells of biliary canaliculi &
obstruction of bile with consequent irritation of epithelial cells
leads to secretion of ALP into serum.
Drastically high levels of ALP (10-25 times of upper limit) are seen
in bone diseases where osteoblastic activity is enhanced such as
Paget's disease (osteitis deformans), rickets, osteomalacia,
osteoblastoma, metastatic carcinoma of bone and
hyperparathyroidism.
Enzyme profiles in liver diseases
Enzymes commonly studied for diagnosis of liver diseases
are:
Alanine amino transaminase (ALT)
Alkaline phosphatase (ALP)
Nucleotide phosphatase (NTP)
Gamma glutamyl transferase (GGT)
Nucleotide Phosphatase (NTP)
It is also known as 5' nucleotidase.
This enzyme hydrolyses 5' nucleotides to corresponding nucleosides
at an optimum pH of 7.5.
Nickel ions inhibit NTP but not ALP.
It is a marker enzyme for plasma membranes and it is ecto-enzyme
Normal NTP level in serum is 2-10 IU/L.
It is moderately increased in hepatitis and highly elevated in biliary
obstruction.
Unaffected by bone diseases.
Gamma Glutamyl Transferase (GGT)
It can transfer gamma glutamyl residues to substrate. In the body it is used in the synthesis of glutathioneGGT has 11 iso-enzymes. It is seen in liver, kidney, pancreas, intestinal cells & prostate
gland.Normal serum value of GGT is 10-30 U/L.It is moderately increased in infective hepatitis and prostate
cancersGGT is clinically important because of its sensitivity to detect
alcohol abuse. GGT is increased in alcoholics.Increase in GGT level is generally proportional to the amount of
alcohol intake.
Enzyme profiles in muscle diseases
Enzymes commonly studied for diagnosis of muscle diseases are:
AST
CPK
Aldolase
In muscular dystrophies, probably due to increased leakage of
enzymes from damaged cells.
CPK is most reliable indicator of muscular diseases.
Aldolase
It is a tetrameric enzyme with A and B subunits; so there
are 5 iso-enzymes.
It is a glycolytic enzyme.
Normal range of serum is 1.5-7 U/L.
It is drastically elevated in muscle damages such as
progressive muscular dystrophy, poliomyelitis, myasthenia
gravis and multiple sclerosis.
It is a very sensitive early index in muscle wasting
diseases.
Enzyme profiles in bone diseases
Serum alkaline phosphatase remains the only useful
enzyme assay for investigation.
ALP is most valuable index of osteoblastic activity.
Increased ALP activity is seen in rickets, osteomalacia,
hyperparathyroidism & in Paget’s disease.
In malignancies of bone, the level depends on the severity
& degree of new bone formation.
In hypophosphatasia, where there is defective calcification,
low serum ALP activity is observed.
Enzyme profiles in malignancies
Enzymes commonly studied for diagnosis of malignancies are:
Serum acid phosphatse (ACP)
Serum prostate specific antigen (PSA)
Serum enolase
Serum alkaline phosphatase (ALP)
Serum LDH
Serum aldolase
β-Glucuronidase
Serum acid phosphatase (ACP)
It hydrolyses phosphoric acid ester at pH between 4 and 6.
Normal serum value for ACP is 2.5-12 U/L.
ACP is secreted by prostate cells, RBC, platelets and WBC.
The prostate iso-enzyme is inactivated by tartaric acid.
Normal level of tartrate labile fraction of ACP is 1 U/L.
ACP total value is increased in prostate cancer and highly
elevated in bone metastasis of prostate cancer.
In these conditions, the tartrate labile iso-enzyme is elevated.
Very helpful in follow-up of treatment of prostate cancers.
Prostate specific antigen (PSA)
It is produced from the secretory epithelium of prostate
gland.
It is normally secreted into seminal fluid, where it is
necessary for the liquefaction of seminal coagulum.
It is a serine protease, and is a 32 kD glycoprotein.
In blood it is bound to alpha-2-macroglobulin and alpha-1-
antitrypsin; a very small fraction is in the free form also.
Normal value is 1-5 microgram/L.
It is very specific for prostate activity.
Values above 10 microgram/L is indicative of prostate
cancer.
Enolase
It is a glycolytic enzyme.
Neuron-specific enolase (NSE) is an iso-enzyme seen in neural
tissues
NSE is a tumor marker for cancers associated with
neuroendocrine origin, small cell lung cancer, neuroblastoma,
pheochromocytoma, medullary carcinoma of thyroid, etc.
It is measured by RIA or ELISA.
β-Glucuronidase
Not routinely done.
β-Glucuronidase most abundant in liver, spleen,
endometrium, breast & adrenals.
Leukocytes contain high content.
Increased levels are seen in cancer of urinary bladder.
Very high levels are seen in carcinoma of head of pancreas &
in 50% cases of breast cancer.
Enzyme profiles in pancreatic diseases
Amylase
The enzyme splits starch to maltose & activated by Ca2+ & Cl-
ions.
It is produced by pancreas and salivary glands.
Normal serum value is 50-120 IU/L.
The value is increased about 1000 times in acute pancreatitis
which is a life-threatening condition.
The peak values are seen between 5-12 hours after the onset of
disease and returns to normal levels within 2-4 days after the
acute phase has subsided.
Moderate increase in serum levels are seen in chronic
pancreatitis, mumps (parotitis) and obstruction of pancreatic
duct.
Normal value of amylase in urine is less than 375 U/L.
It is increased in acute pancreatitis.
It is increased on the 1st day and remains to be elevated for 7-
10 days.
lipase
It will hydrolyse triglyceride to beta-monoglyceride and fatty
acid.
The enzyme is present in pancreatic secretion.
The level in blood is highly elevated in acute pancreatitis and this
persists for 7-14 days.
Lipase remains elevated longer than amylase.
Lipase is not increased in mumps.
Lipase estimation has advantage over amylase.
It is moderately increased in carcinoma of pancreas, biliary
diseases and perforating peptic ulcers.
Cholinesterase (ChE)
Acetyl cholinesterase or true ChE or Type 1 ChE can act mainly on acetyl
choline.
It is present in nerve endings and in RBCs.
Newly formed RBC will have high levels of ChE which is slowly reduced
according to the age of the cell.
ChE level in RBCs will be proportional to the reticulocyte count.
Organophosphorus insecticides (Parathione) irreversibly inhibit ChE in
RBCs.
Measurement of ChE level in RBCs is useful to determine the amount of
exposure in persons working with these insecticides
Pseudo cholinesterase or type II ChE is nonspecific and can
hydrolyse acyl esters.
It is produced mainly by liver cells.
Succinyl choline is a widely used muscle relaxant.
It is a structural analogue of ACh, and competitively fixes on post-
synaptic receptors of ACh.
Succinyl choline is hydrolysed by the liver ChE within 2–4 minutes.
But in certain persons the ChE activity may be absent; this is a
genetically transmitted condition.
In such individuals when succinyl choline is given during surgery,
it may take hours to get the drug metabolized.
Glucose-6-phosphate Dehydrogenase
It is a dimer with identical subunits.
It is an important enzyme in the hexose monophosphate shunt
pathway of glucose
It is mainly used for production of NADPH.
Hydrogen peroxide is continuously formed inside the RBC.
Peroxide will destroy RBC cell membrane.
Glutathione and NADPH will prevent this process.
NADPH is very essential for preserving the RBC integrity.
Drug Induced Hemolytic Anemia
Normal value of GPD in RBC is 6-12 U/g of Hb.
This is reduced in drug induced hemolytic anemias.
In the GPD deficient individuals, RBC life-span may be reduced, but
there will be no disease manifestations.
But when certain drugs (aspirin, mepacrine, primaquine, sulpha) are
taken by such individuals, there will be sudden damage to RBCs.
Primaquin stimulates peroxide formation.
In G6PD deficient cells the level of NADPH is low, leading to
unchecked build up of peroxides resulting in premature cell lysis.
This drug-induced hemolytic anemia is characteristic of GPD
deficiency
Therapeutic use of enzymes
Enzyme Therapeutic application
Asparaginase Acute lymphoblastic leukemia
Streptokinase To lyse intravascular clot
Urokinase To lyse intravascular clot
Pancreatin (trypsin & lipase) Pancreatic insufficiency; oral administration
Papain Anti-inflammatory
Alpha-1-antitrypsin AAT deficiency; emphysema
Enzymes used for diagnostic purpose
Enzyme Used for testing
Urease Urea
Uricase Uric acid
Glucose oxidase Glucose
Peroxidase Glucose, Cholesterol
Hexokinase Glucose
Cholesterol oxidase Cholesterol
Lipase Triglycerides
Alkaline phosphatase ELISA
Horse radish peroxidase ELISA
Restriction endonuclease Southern blot; RFLP
Reverse transcriptase Polymerase chain reaction (RT=PCR)
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