Bmm480 Enzymology

1. BMM480 ENZYMOLOGY

2. CLINICAL ENZYMOLOGY
• Clinical correlations of enzymes
• Enzymes as markers for diagnosis
• Enzyme abnormalities in metabolisms
• Enzymes used in therapy
• Enzymes as target of drug
Medical
applications of
enzymes

3. Clinical enzymology refers to measurement of enzyme activity
for the diagnosis and treatment of diseases
• A human cell contains 28,602 different proteins, 2,709 proteins of which are
enzymes.
• They have assigned roles in ~ 135 metabolic pathways (2,645 metabolites)
• They are distributed in: cytosol, nucleus, rough and smooth ER, Golgi bodies,
mitochondria, lysosomes, plasma and organelle membranes.
• The enzymes are mainly synthesized in cytosol or ER (stay, or target to other
organelles and export to extracellular environment, or extracellular enzymes).
• Relatively small numbers are synthesized in the mitochondria and these enzymes
stay within this space.
• The activity of an intracellular enzyme is determined by the
– rates of synthesis,
– inactivation and
– degradation (= turnover).

4. CLINICAL ENZYMOLOGY
Measurements of the activity of enzymes in plasma are of value in the diagnosis and
management of a wide variety of diseases.
• Most enzymes are present in cells at much higher concentrations than in plasma.
• Some occur predominantly in cells of certain tissues.
Why is that so? Why don’t we measure the enzyme activities directly in the cells? Why is
measuring plasma enzymes important?

5. 1) Plasma contains many functional enzymes, which are actively secreted into plasma.
– many enzymes, for example renin, complement factors and , enzymes of blood coagulation, are actively secreted into
the blood, where they fulfil their physiological functions.
2) On the other hand, there are a few non functional enzymes in plasma, which are coming out from
cells of various tissues due to normal wear and tear.
• Their normal levels in blood are very low; but are drastically increased during cell death (necrosis) or
disease.
a) Most enzymes measured in plasma are primarily intracellular, being released into the blood when there is
damage to cell membranes,
b) Small amounts of intracellular enzymes are present in the blood as a result of normal cell turnover.
• Therefore assays of these enzymes are very useful in diagnosis of diseases.
CLINICAL ENZYMOLOGY

6. When damage to cells occurs, increased
amounts of enzymes will be released
and their concentrations in the blood
will rise.
Mechanism of enzyme release from damaged cell
However, such increases are not always due to tissue damage.
• Read: https://www.ncbi.nlm.nih.gov/pubmed/7813251
Release of intracellular enzymes to the extracellular space is a marker of
cell damage in various diseases, e.g. liver, heart and muscle diseases.
In the normal state the plasma membrane is impermeable to enzymes,
and enzyme release, therefore, indicates a severe change of the
membrane integrity.
cellular changes lead to enzyme release, which may be caused either by
energy depletion, e.g. in ischemia or shock, or by a direct membrane
damage as caused by various toxins and inflammatory products.
CLINICAL ENZYMOLOGY

7. • The normal levels in plasma reflect the balance between the rate of
synthesis and release into plasma during cell turnover, and the rate of
clearance from the circulation.
• The enzyme level in plasma may be:
increased due to
• proliferation of cells (e.g. neoplasia)
• an increase in rate of cell turnover or damage
• an increase in enzyme synthesis (enzyme induction)
• obstruction to secretion (obstruction of bile duct increases
alkaline phosphatase)
• reduced clearance from plasma
lower than normal, due to
reduced synthesis,
congenital deficiency.
CLINICAL ENZYMOLOGY
Little is known about the mechanisms by which enzymes are
removed from the circulation.
Small molecules, such as amylase, are filtered by the
glomeruli but most enzymes are probably removed by
reticuloendothelial cells.
Plasma amylase activity rises in acute renal failure but, in
general, changes in clearance rates are not known to be
important as causes of changes in plasma enzyme levels.

8. Medical Importance of Non-functional enzymes
• Measurement of these enzymes is important for:
***Diagnosis of disease – disease of different organs cause
elevation of different plasma enzymes
***Prognosis of the disease --- follow up treatment pre and post
measurement of enzymes

9. Plasma enzyme patterns in disease: diagnosis &
monitor
Time sequence of changes in plasma enzymes after myocardial
infarction(hours, h; days, d)

10. Some Serum Enzymes of Clinical Interest
Common name Abbreviation Diagnostic Purpose
Aldolase ALD Muscle disorders
Alkaline Phosphatase ALP Bone and liver disorders
Acid Phosphatases ACP Prostate cancer
Amylase Acute pancreatitis
Creatine Phosphokinase CPK or CK Myocardial infarction
Muscle disease
-Glutamyl Transpeptidase GGT Liver disease
Aspartate Aminotransferase AST or GOT Liver disease
Alanine Aminotransferase ALT or GPT Liver disease
Guanine Deaminase GDS Liver disease
Lactate Dehydrogenase LDH or LD Myocardial infarction
Liver disease
Malignancies

11. Common name Abbreviation Diagnostic Purpose
Leucine Aminotranspeptidase LAP Pancreatic carcinoma
Acute pancreatitis
Liver diseases
Lipase Acute pancreatitis
5'-Nuclease NTP Liver disease
Ornithine-Carbamoyl Transferase OCT Liver disease
Pseudocholinestarase Exposure to organophosphates
Some Serum Enzymes of Clinical Interest

12. • What is the preferred biological fluid used in clinical enzymology ?
(used as enzyme source?)
– Serum or plasma is generally used.
• What else?
– Cerebrospinal fluid, biopsy samples etc.
• Difference between serum and plasma ? How can we obtain serum? How
can we obtain plasma?

13. Plasma
• Plasma is the fluid portion of the blood.
• In order to obtain the plasma, peripheral blood is collected into anticoagulant-
treated tubes. Anticoagulants are EDTA, heparin, citrate.
• And then the tube is centrifuged and supernatant is plasma.
** Learn how the anticoagulants prevent coagulation. (Homework )
** after centrifugation what is in the pellet ?
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14. Serum
How serum is obtained ?
 Blood is collected into empty tubes (it is called serum tube – it doesn’t contain
any anticoagulant)
 Allow the blood to clot at room temperature by leaving it undisturbed
 Centrifuge
 The supernatant is serum
 What is in the pellet ?
The difference between plasma and serum is:
Plasma contains the fibrinogen and other coagulation factors.
In the serum these factors have clotted and therefore are in the
pellet.
PLASMA = SERUM + COAGULATION FACTORS
14

15. Enzyme Units
• Enzyme assays usually depend on the measurement of the catalytic activity of the
enzyme, rather than the concentration of the enzyme protein itself.
• Since each enzyme molecule can catalyze the reaction of many molecules of
substrate, measurement of activity provides great sensitivity.
• It is, however, important that the conditions of the assay are optimized and
standardized to give reliable and reproducible results.
• Reference ranges for plasma enzymes are dependent on assay conditions, for
example temperature, and may also be subject to physiological influences.
• It is thus important to be aware of both the reference range for the laboratory
providing the assay and the physiological circumstances when interpreting the
results of enzyme assays.

16. • One international unit is the amount of enzyme that will convert one
micromole of substrate per minute.
per litre of sample and is abbreviated as U/L.
• The SI Unit (System Internationale) expression is more scientific
One Katal (catalytic activity) is defined as the amount of enzyme that
converts 1 mole of substrate per second
Katal is abbreviated as kat or k (60 U = 1 μkat and 1 nk = 0.06 U).

17. Disadvantages of enzyme assays
• A major disadvantage in the use of enzymes for the diagnosis of tissue damage is
their lack of specificity to a particular tissue or cell type. Many enzymes are
common to more than one tissue, with the result that an increase in the plasma
activity of a particular enzyme could reflect damage to any one of these tissues.
• This problem may be obviated to some extent in two ways:
1) first, different tissues may contain (and thus release when they are damaged)
two or more enzymes in different proportions;
Thus, alanine and aspartate aminotransferases are both present in cardiac and
skeletal muscle and hepatocytes, but there is only a very little alanine
aminotransferase in either type of muscle.
Most increases in Alanine aminotransferase
levels are caused by liver damage.

18. 2) second, some enzymes exist in different forms (isoforms), colloquially
termed isoenzymes (although, strictly, the term 'isoenzyme' refers only to a
genetically determined isoform).
• Individual isoforms are often characteristic of a particular tissue:
although they may have similar catalytic activities, they often differ in
some other measurable property, such as heat stability or sensitivity to
inhibitors.

19. 3) Timing is important
• After a single insult to a tissue, the activity of intracellular enzymes in the
plasma rises as they are released from the damaged cells, and then falls as
the enzymes are cleared.
• It is thus important to consider the time at which the blood sample is
taken in relation to the insult.
• If taken too soon, there may have been insufficient time for the enzyme to
reach the blood- stream and if too late, it may have been completely
cleared.
• As with all diagnostic techniques, data acquired from measurements of
enzymes in plasma must always be assessed in the light of whatever
clinical and other information is available, and their limitations borne in
mind !!!

20. • What does LDH do in the cell ?
LACTATE DEHYDROGENASE (LDH) (LD)
When animal tissues cannot be supplied with
sufficient oxygen to support aerobic oxidation of
the pyruvate and NADH produced in glycolysis,
NAD is regenerated
from NADH by the reduction of pyruvate to
lactate.
Some tissues and cell types (such as
erythrocytes, which have no mitochondria and
thus cannot
oxidize pyruvate to CO2) produce lactate from
glucose
even under aerobic conditions.
The reduction of
pyruvate is catalyzed by lactate dehydrogenase,
which forms the L isomer of lactate at pH 7.
What is the
main purpose
of LDH
enzyme ?

21. LACTATE DEHYDROGENASE (LDH) (LD)
• Normal value of LDH in serum is 100-200 U/L.
• Values the upper range are generally seen in children. Strenuous exercise
will slightly increase the value. LDH level is 100 times more inside the RBC
than in plasma, and therefore minor amount of hemolysis will result in a
false-positive test.
• LDH and Heart Attack
In myocardial infarction, total LDH activity in plasma is increased, while H4 iso-
enzyme is increased 5-10 times more.
• Differential diagnosis: Increase in total LDH level is seen in hemolytic
anemias, hepatocellular damage, muscular dystrophy, carcinomas,
leukemias, and any condition which causes necrosis of body cells. Since
total LDH is increased in many conditions, the study of isozymes of LDH
is of great importance.
• (Method used for detection: The total LDH is generally tested by reaction
of the serum sample with pyruvate and NADH2. LDH will convert pyruvate
to lactate, and in turn NADH is used up by the reaction.)

22. Isoenzymes of LDH
• LDH enzyme is a tetramer with four subunits. But the subunit may be either H
(heart) or M (muscle) polypeptide chains.
• These two are the products of two different genes.
• Although both of them have the same molecular weight (32 kD), there are minor
amino acid variations. So five combinations of H and M chains are possible;
H4, H3M, H2M2, HM3 and M4 varieties,
forming five iso-enzymes.
All these five forms are seen in all persons.
• M4 form is seen in skeletal muscles; it is not inhibited by pyruvate.
• But H4 form is seen in heart and is inhibited by pyruvate.
• Normally LDH-2 (H3M1) concentration in blood is greater than LDH-1 (H4); but
this pattern is reversed in myocardial infarction; this is called flipped pattern.
LACTATE DEHYDROGENASE (LDH) (LD)

23. • The iso-enzymes are usually separated by cellulose
acetate electrophoresis at pH 8.6.
• They are then identified by adding the reactants finally producing a colour
reaction.
• Lactate dehydrogenase isoenzymes (as percentage of total):
• LDH1 14-26 %
• LDH2 29-39 %
• LDH3 20-26 %
• LDH4 8-16%
• LDH5 6-16 %
LACTATE DEHYDROGENASE (LDH) (LD)

24. • What does CK do in the cell ?
• It is used for the reaction shown below:
Creatine → Creatine phosphate
• It was called as creatine phosphokinase in old literature.
Normal serum value for CK is 15-100 U/L for males and 10-80 U/L for females.
• CK and Heart Attack CK value in serum is increased in myocardial
infarction. The CK level starts to rise within three hours of infarction.
Therefore, CK estimation is very useful to detect early cases, where ECG
changes may be ambiguous.
** The CK level is not increased in hemolysis or in congestive cardiac failure; and
therefore CK has an advantage over LDH.
CREATINE KINASE (CK)

25. CK and Muscle Diseases
• The level of CK in serum is very much elevated in muscular dystrophies
(500 -1500 IU/L).
• The level is very high in the early phases of the disease. In such patients a
fall in CK level is indicative of deteriorating condition, because by that
time, all muscle mass is destroyed.
• In female carriers of this X-linked disease (genotypically heterozygous), CK
is seen to be moderately raised.
• CK level is highly elevated in crush injury, fracture and acute
cerebrovascular accidents.
• Estimation of total CK is employed in muscular dystrophies and MB iso-
enzyme is estimated in myocardial infarction.
CREATINE KINASE (CK)
Normal serum value for CK is 15-100 U/L for males
and 10-80 U/L for females.

26. • Iso-enzymes of CK
CK is a dimer; each subunit has a molecular weight of 40,000. The subunits
are called B for brain and M for muscle.
They are products of loci in chromosomes 14 and 19 respectively. Therefore
three iso-enzymes are seen in circulation.
• CK-1: CK-MM, found in skeletal muscle and heart
• CK-2: CK-MB, found in the heart and rises when heart muscle is damaged
• CK-3: CK-BB, found mostly in brain
Normally CK-2 is only 5% of the total activity.
CREATINE KINASE (CK)
The above three iso-enzymes are cytosolic normally.

27. Even doubling the value in CK-2 (MB) iso-enzyme may not be detected, if total value of
CK alone is estimated.
Hence the detection of MB-iso-enzyme is important in myocardial infarction. (CK-2)
CK-MB < 6 % of total CK in normal conditions.
CREATINE KINASE (CK)
HOW is MB iso-enzyme detected ?
For quantitating MB iso-enzyme, anti-MM antiserum is
added to the patient's serum.
This will precipitate MM iso-enzyme. The supernatant
serum is used for the CK estimation.
Here it is assumed that BB isoenzyme is negligible in
quantity, which is correct if there is no brain disease.
CK iso-enzymes can also be identified by
electrophoresis.

28. CREATINE KINASE (CK)
• A fourth variety, called CK-mt is located in mitochondria and constitutes
about 15% of total CK activity. Its gene is located in chromosome 15.
Troponin is a good marker for myocardial infarction
Troponin is not an enzyme, so not discussed in this course

29. Enzyme abnormalities in metabolism

30. Excess enzyme activity
• Gout is characterized by elevated uric acid levels in blood and urine, due
to overproduction of de novo purine nucleotides.
• E.g., Excess PRPP synthase activity (X-linked recessive inheritance pattern)
purine nucleotides
then leads to increase degradation of purines to uric acid through xanthine
oxidase.

31. Enzyme deficiency
• Enzyme deficiencies usually lead to increased accumulation of specific
metabolites in plasma and hence in urine.
• This is useful in pinpointing enzyme defects.
• E.g., De novo pyrimidine pathway: defects of OPRT and OMPDC leads to
accumulation of orotate ----> Hereditary orotic aciduria (Gene mapping,
3q13; inheritance pattern, autosomal recessive).

32. Major Classes of Metabolic Disorders
• Enzyme defects cause metabolic disorders
• Inborn errors of metabolism based upon the type of chemical
process involved

33. Disorders of Amino Acid Metabolism
Disease
Defective Enzyme or
System
Symptoms Treatment
Phenylketonuria
(PKU)
phenylalanine
hydroxylase
severe mental
retardation
screening; dietary
modification
Malignant PKU biopterin cofactor neurological disorder —
Type 1 tyrosinemia
fumarylacetoacetate
hydrolase
nerve damage, pain,
liver failure
liver transplantation;
preceding enzyme
inhibitor plus dietary
modification
Type 2 tyrosinemia
tyrosine
aminotransferase
irritation to the
corneas of the eyes
diet with reduced
phenylalanine and
tyrosine content
Alkaptonuria
disorder of tyrosine
breakdown
progressive arthritis
and bone disease;
dark urine
—

34. Phenylketonuria
• Phenylketonuria (PKU) is the most common disorder of amino acid metabolism,
and it is a paradigm for effective newborn screening.
• Phenylalanine is an essential amino acid (meaning that it cannot be synthesized
but must be taken in through the diet).
• The first step to its breakdown is the phenylalanine hydroxylase reaction, which
converts phenylalanine to another amino acid, tyrosine.

35. • A genetic defect in the phenylalanine hydroxylase enzyme is the basis for
classical PKU.
• Untreated PKU results in severe mental retardation.
• PKU can be detected by screening newborn blood spots, and the classical
form can be very effectively treated by using medical formulas that are
limited in their phenylalanine content.
• The hydroxylase enzyme requires a cofactor called biopterin, which is also a
cofactor for other enzymes.
• Defects affecting the production of biopterin result in another form, so-called
malignant PKU.
• In this form, the other biopterin-dependent hydroxylases are also affected,
resulting in deficient neurotransmitter synthesis and significant neurological
symptoms.
Phenylketonuria

36. • When Phe cannot be metabolized by the body, a typical diet that would be
healthy for people without PKU causes abnormally high levels of Phe to
accumulate in the blood, which is toxic to the brain.
• If left untreated, complications of PKU include severe intellectual
disability, brain function abnormalities, microcephaly, mood disorders,
irregular motor functioning, and behavioral problems such as attention
deficit hyperactivity disorder, as well as physical symptoms such as a
"musty" odor, eczema, and unusually light skin and hair coloration.
Phenylketonuria

37. Disease
Defective Enzyme or
System
Symptoms Treatment
Homocystinuria and
Hyperhomocysteinemia
cystathionine-β-synthase
or
methylenetetrahydrofola
te reductase or various
deficiencies in formation
of the methylcobalamin
form of vitamin B12
hypercoagulability of
the blood; vascular
eposides; dislocation of
the lens of the eye,
elongation and
thinning of the bones,
and often mental
retardation or
psychiatric
abnormalities
vitamin B12, folic acid,
betaine, a diet limited in
cysteine and methionine
Maple Syrup Urine
disease
branched-chain ketoacid
dehydrogenase complex
elevations of
branched-chain amino
acids, characteristic
odor of the urine,
episodes of
ketoacidosis, death
thiamine; careful
regulation of dietary
intake of the essential
branched-chain amino
acids
Disorders of Amino Acid Metabolism

38. Disorders of Organic Acid Metabolism
Disease
Defective Enzyme or
System
Symptoms Treatment
Propionic Acidemia
propionyl-CoA
carboxylase
generalized metabolic
dysfunction;
ketoacidosis; death
diet with limited
amounts of the amino
acids which are
precursors to
propionyl-CoA
Multiple
Carboxylase
deficiency
pyruvate carboxylase
and 3-
methylcrotonyl-CoA
carboxylase
— biotin
Methylmalonic
Acidemia
methylmalonyl-CoA
mutase; defects in
the enzyme systems
involved in vitamin
B12 metabolism
—
supplementation with
large doses of vitamin
B12; diet

39. Disorders of Fatty Acid Metabolism
Disease
Defective Enzyme or
System
Symptoms Treatment
Hyperlipidemia and
hypercholesterolemia
regulation or utilization of
lipoproteins
cardiovascular
disease
dietary modifications and use of
drugs that inhibit fatty acid
synthesis.
Fatty Acid Oxidation
disorders
very long chain acyl-CoA
dehydrogenase; long
chain hydroxyacyl-CoA
dehydrogenase;
dehydrogenase; medium
chain acyl-CoA
dehydrogenase; short
chain acyl CoA
dehydrogenase; short
chain hydroxyacyl-CoA
dehydrogenase
low blood sugar
(hypoglycemia);
muscle weakness;
cardiomyopathy
avoidance of fasting,
intravenous glucose solutions;
carnitine; medium chain
triglycerides

40. Disease
Defective Enzyme or
System
Symptoms Treatment
Glycogen Storage diseases defects in glycogenolysis
liver enlargement or
damage; muscle
weakening or
breakdown; disturbed
renal tubular function;
risk of brain damage
—
Galactosemia
galactose-1-phosphate
uridyl transferase
liver failure in infancy
newborn screening;
milk avoidance
Congenital Disorders of
Glycosylation
defects in the enzymes that
build the carbohydrate
side-chains on proteins
quite variable;
multisystem
—

41. Disorders of Purine and Pyrimidine Metabolism
Disease
Defective Enzyme or
System
Symptoms Treatment
Purine Overproduction
imbalance between
purine synthesis and
disposal
gout —
Lesch-Nyhan syndrome
hypoxanthine
phosphoribosyl-
transferase
defective salvage of
purines; increase in the
excretion ofuricacid; brain
neurotransmitter
dysfunction; severe spastic
movement disorder; self-
injurious behavior
allopurinol (does not
treat neurological
symptoms)

42. Gout
• Purines and pyrimidines are chemicals that form the nucleic acids (DNA and
RNA).
• An important purine compound is adenosine triphosphate (ATP), which is used
to transfer chemical energy for processes such as biosynthesis and transport.
• There are several rare defects in the synthesis of purines and pyrimidines.
• The most common symptom of purine overproduction is gout, which arises for
several reasons, often not associated with an identifiable enzyme defect but
rather due to an imbalance between purine synthesis and disposal.
• Gout manifests when the ultimate product of purine degradation, uric acid,
accumulates and crystallizes in the joints.

43. Lysosomal Storage Disorders
Disease
Defective Enzyme or
System
Symptoms Treatment
Gaucher disease Types I
and II
cerebrosidase
enlargement of the
spleen and liver; painful
and crippling effects on
the bones; severe brain
disease and death (Type
II)
enzyme replacement
(Type I)
Tay-Sachs disease beta-hexosaminidase A
neurological disorders;
enlarged head; death in
early childhood
—
Fabry disease α-galactosidase
severe pain; renal failure;
heart failure
enzyme replacement

44. Disease Defective Enzyme or System Symptoms Treatment
Hurler syndrome, Hunter
syndrome
α-iduronidase (Hurler
syndrome);iduronate sultatase
(Hunter syndrome) iduronate
sultatase (hunter syndrome)
enlargement of the liver and
spleen; skeletal deformities;
coarse facial features; stiff
joints; mental retardation;
death within 5-15 years
enzyme
replacement
Sanfilippo syndrome
enzymes for heparan sulfate
degradation
enlargement of the liver and
spleen
enzyme
replacement
Maroteaux-Lamy
syndrome
arylsulfatase B
progressive, crippling and
life-threatening physical
changes similar to Hurler
syndrome, but generally
with normal intellect
—
Morquio syndrome
galactose 6-sulfatase; β-
galactosidase
truncal dwarfism; severe
skeletal deformities;
potentially life-threatening
susceptibility to cervical
spine dislocation; valvular
heart disease
Lysosomal Storage Disorders

46. Disorders of Peroxisomal Metabolism
Disease
Defective Enzyme or
System
Symptoms Treatment
Disorders of Urea
Formation
carbamyl phosphate
synthetase deficiency;
ornithine
transcarbamylase
deficiency, citrullinemia,
argininosuccinic aciduria
hyperammonemia;
mental retardation;
seizures; coma; death
limitation of dietary
protein; phenylacetate;
liver transplantation
Disease
Defective Enzyme or
System
Symptoms Treatment
Refsum disease
branched-chain fatty acid
buildup
neurologic symptoms —
Alanine-glyoxylate
transaminase defect
alanine-glyoxylate
transaminase
oxalic acid increase; organ
dysfunction; renal failure
liver transplantation

47. Enzyme defects found in all human metabolisms
• Examples of enzyme defects.