Medical Applications of Enzymes

Enzymes in Clinical Diagnosis

Most enzymes are confined within the cells of the body.

However, small amounts of enzymes can also be found in body fluids,

such as blood, urine, and cerebrospinal fluid,

because of the normal breakdown and replacement of tissue cells

that goes on constantly.

However, blood serum levels of cellular enzymes increase significantly,

when excessive tissue injury or destruction occurs or

when cells grow rapidly as a result of cancer.

These enzyme levels can be easily monitored.

The measurement of enzyme concentrations in blood serum and

other biological fluids has become a major diagnostic tool.

It is used in the diagnosis of heart, liver, pancreas, prostate or bone diseases.

For example: The concentration of enzymes in the blood is measured during

myocardial infarction in order to diagnose the severity of the heart attack.

During a heart attack and immediately after, dead heart muscle cells spill

their enzyme content into the serum.

The levels of aspartate aminotransferase (AST), lactate dehydrogenase

(LD-P) and cretatine kinase (CK) rises rapidly in the serum are monitered.

How can we tell that these enzymes come from the heart and not other parts of the body? The same enzymes found in different parts of the body are slightly different.

isoenzymes (or isozymes) - are slightly different forms of the same enzyme

produced by different tissues.

For example: Lactate dehydrogenase (LP-D) catalyzes the conversion of lactate to

pyruvate, and vice versa.

This enzyme has four subunits.

Two kinds of subunits exist, called H & M.

The isoenzyme that dominates in the heart is an H₄,

meaning all four subunits are of the H type,

although some M type subunits are also present.

In the liver and skeletal muscles the M type dominates.

Other types of tetramer (four units) combinations exist in different tissues.

H₃M, H₂M₂, HM₃

In diagnosing the severity of heart attacks, the release of H₄ isoenzyme is

monitored in the serum.