Faculty of nursing CHEM 203 Biochemistry UNIT VIII Diagnostic Enzymes Dr.Ola Fouad Talkhan.

Dr.Ola Fouad Talkhan

Faculty of nursing

CHEM 203 Biochemistry

UNIT VIII

Diagnostic Enzymes


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.


•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.


1- ALTERATION OF PLASMA ENZYME LEVELS IN DISEASE STATES

•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.


2- PLASMA ENZYMES AS DIAGNOSTIC TOOLS: •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.


C. ISOENZYMES AND DISEASES OF THE HEART:

•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.


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.


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


Serum enzyme Major diagnostic use

Aminotransferases aspartate aminotransferase

AST,or SGOT

alaninaminotransferase ALT,or SGPT

Y-glutamyl transferase

Amylase

Creatin kinase

Phosphatase,acid

Phosphatase,alkaline

Lipase

Lactate dehydrogenase isozyme5

ceruloplasmin

Myocardial infarction ,liver dis.

viral hepatitis

Various Liver diseases

Acute pancreatitis ,GIT disorders

Myocardial infarction, muscle disorders

Metastatic carcinoma of the prostate

Various bone disorders, obstructive liver diseases

Acute pancreatitis

Liver diseases

Hepatolenticular degeneration( Wilson’s dis.)


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


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


Liver function testes Enzymes in diagnosis of liver

disease

Serum transaminasesALTAST

Serum alkaline phosphataseALP


• 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

Enzymes in diagnosis of liver disease

Serum transaminases

Serum alkaline phosphatase


Serum transaminasesAST or SGOT=<35U/LALT or SGPT=<40U/L

S. alkaline phosphataseALP= 3-13KA units/dlALP is normally excreted through bile↑↑↑In obstructive jaundice

Enzymes in liver disease


Enzyme Prehepatic Jaundice

Hepatic Jaundice

Obstructive Jaundice

ALT or AST Usually normal Marked increase500-1500IU/L

Increased 100-300IU/L

ALP Normal Increased slightly< 30KA/dl

Marked increase>30KA/dl

Enzyme assays in differential diagnosis of Jaundice


Serum γ-Glutamyl Transferase

• Normal range: 10-47IU/L

Serum 5’-Nucleotidase


Serum Lactate Dehydrogenase


Other enzymes


Alkaline phosphatasesAlkaline phosphatase (ALP) belongs to a group of enzymes that catalyze the hydrolysis of various phosphomonoesters at an alkaline pH.

Tissue SourceALP 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.


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.


Acid PhosphataseAcid phosphatase (ACP) belongs to the same group ofphosphatase 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 SourceACP 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.


Diagnostic SignificanceHistorically, ACP measurement has been used as an aidin the detection of prostatic carcinoma, particularlymetastatic 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


AmylaseAmylase (AMS) is an enzyme belonging to the class ofhydrolases that catalyze the breakdown of starch andglycogen.

AMS requires calcium and chloride ions for its activation.

Tissue SourceThe acinar cells of the pancreas and the salivary glandsare the major tissue sources of serum AMS. Lesser concentrationsare found in skeletal muscle and the small intestineand fallopian tubes. AMS is the smallest enzyme,


Other disorders causing an elevated serum AMS levelinclude 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.

Faculty of nursing CHEM 203 Biochemistry UNIT VIII Diagnostic Enzymes Dr.Ola Fouad Talkhan.

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