Enzymes in Clinical Diagnosis
- Those, relatively, small group of enzymes secreted into the plasma by certain organs (i.e. Enzymes those have function in plasma) For example: - the liver secretes zymogens of the enzymes involved in blood coagulation.
- Those large enzyme species released from cells during normal cell turnover. These enzymes are normally intracellular and have no physiologic function in the plasma. In healthy individuals the levels of these enzymes are fairly constant and represent steady state in which the rate of release from cells into the plasma is balanced by an equal rate or removal from the plasma.
Measurement of enzymes concentration of mostly the latter type in plasma gives
valuable informatio0n about disease involving tissues of their origin.
Lipase
It is an enzyme catalyzing the hydrolysis of fats. It is secreted by pancreas and Liver.
The plasma lipase level may be low in liver disease, Vitamin A deficiency, some
malignancies, and diabetes mellitus. It may be elevated in acute pancreatitis and
pancreatic carcinoma.
α- Amylase
α- amylase is the enzyme concerned with the break down of dietary starch and
glycogen to maltose. It is present in pancreatic juice and saliva as well as in liver
fallopian tubes and muscles. The enzyme is excreted in the Urine. The main use of
amylase estimations is in the diagnosis of acute pancreatitis. The plasma amylase level
may be low in liver disease and increased in high intestinal obstruction, mumps, acute
pancreatitis and diabetes.
Trypsin
Trypsin is secreted by pancreas. Elevated levels of trypsin in plasma occur during
acute pancreatic disease. .
Alkaline phosphates (ALP)
The alkaline phosphates are a group of enzymes, which hydrolyze phosphate esters at
an alkaline pH. They are found in bone, liver, kidney, intestinal wall, lactating mammary
gland and placenta. In bone the enzyme is found in osteoblasts and is probably
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important for normal bone function. The level of these enzymes may be increased in
rickets and osteomalacia, hyperparathyroidism, paget's disease of bone, obstructive
jaundice, and metastatic carcinoma. Serum alkaline phosphatase levels may be
increase in congestive heart failure result of injury to the liver.
Acid Phosphatase (ACP)
Acid phosphatases catalyzing the hydrolysis of various phosphate esters at acidic pH is
found in the prostate, liver, red cells, platelets and bone. It may be elevated in
metastatic prostatic carcinoma.
Transaminases
Two transaminases are of clinical interest.
- Aspartate Transaminase, AST ( Glutamate oxaloacetate transaminase, GOT ) catalyzes the transfer of the amino group of aspartic acid to α- ketoglutarate forming glutamate and oxaloacetate. AST or GOT is widely distributed, with high concentration, in the heart, liver, skeletal muscle, kidney and erythrocytes, and damage to any of these tissues may cause raised levels.
- Alanine transaminase, ALT (Glutamate pyruvate transaminase, GPT ) Transfer the amino group of alanine to α- ketoglutarate, forming glutamate and pyruvate. It is present in high concentration in liver and to a lesser extent in skeletal muscle, kidney and heart.
Lactate Dehydrogenase (LDH)
It catalyzes the reversible interconversion of lactate and pyruvate. It is widely
distributed with high concentrations in the heart, skeletal muscle, liver, kidney, brain and
erythrocytes.
The enzyme is increased in plasma in myocardial infarction, acute leukemias,
generalized carcinomatosis and in acute hepatitis. Estimation of it isoenzymes is more
useful in clinical diagnosis to differentiate hepatic disease and myocardial infarction.
Creatine kinase (CK) or ceratin phosphokinase (CPK)
CK (CPK) is found in heart muscle brain and skeletal muscle. Measurement of serum
creatine phosphokinase activity is of value in the diagnosis of disorders affecting
skeletal and cardiac muscle. The level of CPK in plasma highly increased in myocardial
infarction.