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Enzymes as

Diagnostic

tools

*The measurement of the serum levels of numerous enzymes has been shown to be of diagnostic significance. *This is because the presence of these enzymes in the serum indicates that tissue or cellular damage has occurred resulting in the release of intracellular components into the blood &this increases the level of certain enzymes in blood according to the damaged organ

How?

What are the enzymes most used in the diagnosis of certain diseases?

Plasma enzymes

Functional Non functional

**For example:-

3-Alanine transminase(ALT) 4-Aspartate transminase(AST)

5-Alkaline phsphatase 6-Acid phosphatase

7-Amylase & Lipase enzymes

Izoenzymes1-Lactate dehydrogenase(LDH)2-Creatine kinase(CK)

Lactate dehydrogenase(LDH)

Lactic acid Pyruvic acid

NAD NADH+H

*LDH is a tetramer(consists of 4 protomers) *the protomers are 2 types:-

1-H(after heart)

2-M(after muscle) so LDH have 5 isoenzymes:-

LDH 1 – Found in heart and red-blood cells and is 17% – 27% of the normal serum total

*It is formed of HHHH.It increases in myocardial infarction

LDH 2 – Found in heart and red-blood cells and is 27% – 37% of the normal serum total.

*It is formed of HHHM.It increases in myocardial infarction LDH 3 – Found in a variety of organs and is 18% – 25% of the normal serum total.

*It is formed of HHMM.It increases in leukaemia LDH 4 – Found in a variety of organs and is 3% – 8% of the normal serum total.

*It is formed of HMMM.It increases in viral hepatitis LDH 5 – Found in liver and skeletal muscle and is 0% – 5% of the normal serum total*It is formed of MMMM.It increases in viral hepatitis

Creatine kinase (CK)

Creatine Ceatine phosphate

ATP ADP

*CK is a dimmer (consists of 2 protomers)

*the protomers are 2 types:

1-B (after brain)

2-M (after muscle)

*so CK has 3 isoenzymes:-

.CPK1 (CPK-BB) is the characteristic isoenzyme in brain and is in significant amounts in smooth muscle and is 0% of the normal serum total.

**It increases in brain tumors.

.CPK2 (CPK-MB) accounts for about 35% of the CPK activity in cardiac muscle , but less than 5% in skeletal muscle and is 0% of the normal serum total.

**It increases in heart diseases.

.CPK3 (CPK-MM) is the predominant isoenzyme in muscle and is 100% of the normal serum total.

**It increases in skeletal muscle diseases.

Alanine transminase(ALT)

*It is also called serum glutamic pyruvic transminase(SGPT)

*ALT is particularly diagnostic of liver involvement as this enzyme is found predominantly in hepatocytes.

*It increases in liver & heart diseases.

*It catalyzes transfer of amino group (NH2) from amino acid (alanine) to a-keto acid producting a new amino acid & a new keto acid

Glutamic oxalacetic transminase(SGOT)

Aspartate transminase(AST)

*It is also called aspartate glutamic oxalacetic transminase(SGOT)

*It increases in liver & heart diseases *When assaying for both ALT and AST the ratio of the level of these two enzymes can also be diagnostic. Normally in liver disease or damage that is not of viral origin the ratio of ALT/AST is less than1.with viral hepatitis the ALT/AST ratio will be greater than1.

*The level of AST elevation in the serum is directly proportional to the number of cells involved as well as on the time following injury that the AST assay was performed. Following injury, levels of AST rise within 8 hours and peak 24–36 hours later. Within 3–7 days the level of AST should return to pre-injury levels unless further injury occurs.

* Although measurement of AST is not, in and of itself, diagnostic for myocardial infarction, taken together with LDH and CK measurements the level of AST is useful for timing of the infarct

Alkaline phosphatase**It is an enzyme which transport phosphate groups across cell membranes of organs.

**It is found in the osteoblasts,bile canali ,small intestinal epithelium and proximal tubule.

**Increases mainly in bone diseases such as Osteogenic sarcoma ,liver & bilary tract diseases and hyperparathyroidism

Acid phosphatase**is found in the prostate, red blood cells, small amounts are found in bone, liver, spleen and pancreas.

**The assay of serum acid phosphatase is mostly used to detect prostatic carcinoma and to monitor the treatment.

**Amylase and lypase enzymes increases in diseases of the pancreas as

acute pancreatitis

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