Transcript diagnostic enzymes,student.ppsx

Faculty of nursing
CHEM 203
Biochemistry
UNIT VIII
Diagnostic
Enzymes
Dr.Ola Fouad Talkhan
Enzymes in Clinical Diagnosis
•Plasma enzymes can be classified into two major groups:
•First, a relatively small group of enzymes are actively
secreted into the blood by certain cell types.
•For example, the liver secretes zymogens (inactive
precursors) of the enzymes involved in blood coagulation.
Dr.Ola Fouad Talkhan
•Second, a large number of enzyme species are
released from cells during normal cell turnover
These enzymes almost always function intracellularly,
and have no physiological use in the plasma.
•In healthy individuals, the levels of these enzymes are
fairly constant, and represent a steady state in which the
rate of release from damaged cells into the plasma is
balanced by an equal rate of removal of the enzyme
protein from the plasma.
•Increased plasma levels of these enzyme may indicate
tissue damage.
Dr.Ola Fouad Talkhan
•Many diseases that cause tissue damage result in an
increased release of intracellular enzymes into the plasma.
•The activities of many of these enzymes are routinely
determined for diagnostic purposes in diseases of the heart,
liver, skeletal muscle, and other tissues.
•The level of specific enzyme activity in the plasma
frequently correlates with the extent of tissue damage.
•Thus, determining the degree of elevation of a particular
enzyme activity in the plasma is often useful in evaluating the
prognosis for the patient.
Dr.Ola Fouad Talkhan
•Some enzymes show relatively high activity in only one or a
few tissues.
•The presence of increased levels of these enzymes in plasma
thus reflects damage to the corresponding tissue.
•For example, the enzyme alanine aminotransferase (ALT) is
abundant in the liver.
•The appearance of elevated levels of ALT in plasma signals
possible damage to hepatic tissue.
•Increases in plasma levels of enzymes with a wide tissue
distribution provide a less specific indication of the site of
cellular injury and limits their diagnostic value.
Dr.Ola Fouad Talkhan
•Most isoenzymes (also called isozymes) are enzymes that
catalyze the same reaction.
•However, they do not necessarily have the same physical
properties because of genetically determined differences in
amino acid sequence.
•For this reason, isoenzymes may contain different numbers of
charged amino acids and may, therefore, be separated from
each other by electrophoresis.
Dr.Ola Fouad Talkhan
Different organs frequently contain characteristic properties
of different isoenzymes.
•The pattern of isoenzymes found in the plasma may,
therefore, serve as a means of identifying the site of tissue
damage.
•For example, the plasma levels of creatine kinase (CK) are
commonly determined in the diagnosis of myocardial
infarction.
•They are particularly useful when the electrocardiogram is
difficult to interpret, such as when there have been previous
episodes of heart disease.
Dr.Ola Fouad Talkhan
Quaternary structure of isoenzymes
•Many isoenzymes contain different subunits in various combinations.
•For example, creatine kinase (CK) occurs as three isoenzymes.
•Each isoenzyme is a dimer composed of two polypeptides (called B
and M subunits) associated in one of three combinations: CK1 = BB,
CK2 = MB, and CK3 = MM.
•Each CK isoenzyme shows a characteristic electrophoretic mobility.
•Note: Virtually all CK in the brain is the BB isoform, whereas in
skeletal muscle it is MM. In cardiac muscle, about one-third is MB
with the rest as MM
Dr.Ola Fouad Talkhan
Serum enzyme
Major diagnostic use
Aminotransferases
aspartate aminotransferase
AST,or SGOT
Myocardial infarction ,liver dis.
alaninaminotransferase
ALT,or SGPT
viral hepatitis
Y-glutamyl transferase
Various Liver diseases
Amylase
Acute pancreatitis ,GIT disorders
Creatin kinase
Myocardial infarction, muscle disorders
Phosphatase,acid
Metastatic carcinoma of the prostate
Phosphatase,alkaline
Various bone disorders, obstructive liver
diseases
Lipase
Acute pancreatitis
Lactate dehydrogenase isozyme5
Liver diseases
ceruloplasmin
Dr.Ola Fouad
Talkhan
Hepatolenticular
degeneration(
Wilson’s dis.)
Dr.Ola Fouad Talkhan
Diagnosis of myocardial infarction
•Measurement of blood levels of proteins with cardiac specificity is
used in diagnosis of myocardial infarction (MI)
because myocardial muscle is the only tissue that contains more than
5% of the total CK activity as the CK2 (MB) isoenzyme.
1-Creatine Kinase
a. Begins to rise 4-6 hours after MI; peak at 24 hrs; returns to
normal in 3-5 days.
b. Isoenzymes: i. CK-MM fraction = found in skeletal muscle
ii. CK-MB fraction = found in heart muscle
iii. CK-BB = found in the brain
Dr.Ola Fouad Talkhan
c. May be increased in other conditions: physical exertion,
postoperatively, convulsions, delirium tremens, etc; hence not
diagnostic for MI unless the CK-MB fraction is being assayed:
rises in 3- 4 hours after MI; peak 12-14 hrs later and returns to
normal in 2 days.
2. Lactate Dehydrogenase
a. Peak level about 36- 40 hrs after MI and thus of diagnostic
value in patients admitted > 48 hrs after infarction.
b. Levels return to normal in 5-14 days
Dr.Ola Fouad Talkhan
Dr.Ola Fouad Talkhan
Dr.Ola Fouad Talkhan
Serum transaminases
ALT
Serum alkaline
phosphatase
AST
ALP
Dr.Ola Fouad Talkhan
•
•
In liver cell injury, damage to the membrane
of cells and organelles allows intracellular
enzymes to leak into the blood.
Where their elevated concentrations can be
measured
Serum transaminases
Serum alkaline phosphatase
Dr.Ola Fouad Talkhan
Dr.Ola Fouad Talkhan
Serum
transaminases
AST or SGOT=<35U/L
ALT or SGPT=<40U/L
S. alkaline
phosphatase
ALP= 3-13KA
units/dl
ALP is normally
excreted through bile
↑↑↑In obstructive
jaundice
Dr.Ola Fouad Talkhan
Enzyme
Prehepatic
Jaundice
Hepatic
Jaundice
Obstructive
Jaundice
ALT or AST
Usually normal
Marked
increase
500-1500IU/L
Increased
100-300IU/L
ALP
Normal
Increased
slightly
< 30KA/dl
Marked
increase
>30KA/dl
Dr.Ola Fouad Talkhan
Serum γ-Glutamyl Transferase
•Normal range: 10-47IU/L
Serum 5’-Nucleotidase
•Normal range: 2-17IU/L
Serum Lactate Dehydrogenase
•Normal range: 70-240IU/L
Dr.Ola Fouad Talkhan
Alkaline phosphatases
Alkaline phosphatase (ALP) belongs to a group of enzymes that catalyze
the hydrolysis of various phosphomonoesters at an alkaline pH.
Tissue Source
ALP activity is present on cell surfaces in most human tissue.
The highest concentrations are found in the intestine, liver, bone, spleen,
placenta, and kidney.
In the liver, the enzyme is located on both sinusoidal and bile canalicular
membranes;
activity in bone is confined to the osteoblasts, those cells involved in the
production of bone matrix.
The specific location of the enzyme within this tissue accounts for the
more predominant elevations in certain disorders.
Dr.Ola Fouad Talkhan
Elevated ALP levels may be observed in various bone
disorders.
Perhaps the highest elevations of ALP activity occur in Paget’s
disease (osteitis deformans).
Other bone disorders include osteomalacia, rickets,
hyperparathyroidism, and osteogenic sarcoma.
In addition, increased levels are observed in healing bone
fractures and during periods of physiologic bone growth.
Dr.Ola Fouad Talkhan
Acid Phosphatase
Acid phosphatase (ACP) belongs to the same group of
phosphatase enzymes as ALP and is a hydrolase that
catalyzes the same type of reactions.
The major difference between ACP and ALP is the pH of the
reaction.
ACP functions at an optimal pH of approximately 5.0.
Tissue Source
ACP activity is found in the prostate, bone, liver, spleen,
kidney, erythrocytes, and platelets.
The prostate is the richest source, with many times the
activity found in other tissue.
Dr.Ola Fouad Talkhan
Diagnostic Significance
Historically, ACP measurement has been used as an aid
in the detection of prostatic carcinoma, particularly
metastatic carcinoma of the prostate.
Total ACP determinations are relatively insensitive
techniques, detecting elevated ACP levels resulting from
prostatic carcinoma in the majority of cases only when the
tumor has metastasized.
Newer markers, such as prostate-specific antigen
(PSA), are more useful screening and diagnostic tools
Dr.Ola Fouad Talkhan
Amylase
Amylase (AMS) is an enzyme belonging to the class of
hydrolases that catalyze the breakdown of starch and
glycogen.
AMS requires calcium and chloride ions for its activation.
Tissue Source
The acinar cells of the pancreas and the salivary glands
are the major tissue sources of serum AMS. Lesser
concentrations
are found in skeletal muscle and the small intestine
and fallopian tubes. AMS is the smallest enzyme,
Dr.Ola Fouad Talkhan
Other disorders causing an elevated serum AMS level
include salivary gland lesions, such as mumps and parotitis,
and other intra-abdominal diseases, such as perforated peptic
ulcer, intestinal obstruction, cholecystitis, ruptured ectopic
pregnancy, mesenteric infarction, and acute appendicitis.
In addition, elevations have been reported in renal
insufficiency and diabetic ketoacidosis.
Dr.Ola Fouad Talkhan