Diagnostic Enzymology (How to calculate enzyme activity)

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Enzymes plays a vital role in catalyzing biochemical reactions reaction which are necessary for normal human growth,maturation and reproduction.

Diagnostic enzymology  involves the measurement of enzymes activities in body fluids in order to diagnose a disease.In most cases,serum or blood are the most useful samples used although urine,cerebrospinal fluid and extracellular fluids are sometimes needed.

Most enzymes used for diagnostic purposes have no direct physiological role in the blood.Their natural presence under normal circumstances is as a result of natural ageing and turn over of living cells.

High level of enzymes in blood can indicate increase cellular turnover (increase enzymatic activity) and necrosis caused by disease.Important and largely overlooked cause of high enzyme level in blood is tissue synthesis of new enzymes that occur in response to disease,induction by various drugs and carcinogenesis for examples in obstructive liver disease,hepatic Alkaline Phosphatase is increased largely because of increase synthesis due to abnormal intracanalicular pressure.Phenobarbital and several other drugs induce microsomal enzyme production that lead to increase production or synthesis of Gamma glutamyl transpeptidase

Enzyme Kinetics (Lock and Key Method)

Action of enzyme (Lock and Key method)
Action of enzyme (Lock and Key method)

Enzymes (E) are biological catalysts that combine with substrate (S) to form intermediate complexes (ES) leading to the formation of products (P)  and restoration of the original enzyme.Reaction involving one substrate exhibit the following kinetic

Enzyme substrate reaction
Enzyme substrate reaction

Some enzymes catalyze more complexe reactions in which there are two or more substrates that form multiple productions.The reactions is a function of several factors including;

  • Substrates and enzyme concentration
  • Temperature
  • pH
  • Presence of cofactors
  • Presence of coenzymes
  • Presence of inhibitors or inhibition

Empirical observation shows that the rate or reaction velocity is proportional to substrate concentration at relatively low values

Also read  3% Sulfosalicylic Acid Test for the Detection of Proteinuria

In diagnostic enzymology,the goal is the measurement of the activity or the concentration of the enzyme itself.Therefore,test condition such that the reaction rate will depend only on the concentration of the enzyme present in the sample to be measured.The substrate concentration should be made sufficient and all other factors that influence the reaction rate should be optimized and controlled.

How to calculate enzymes activity

Enzyme activity can be expressed either in international  unit per litre (Ul) or nanokeital per liltre (nkat/l).Because Beer’s lambert law states that ‘’ Concentration is directly proportional to absorbance”,Enzyme activity each be determined from the change in absorbance per unit time

Calculating enzyme activity
Calculating enzyme activity


  • which enzyme is best used to diagnose alcoholic liver disease?
  • What is the Chemical nature of enzyme

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About the Author: Arthur Westmann

DEFFE ARTHUR (AMOEBAMANN) is the founder and author of MLTGEEKS and MLTEXPO.He’s from Cameroon and is currently a Final year State Medical Laboratory Technician (MLT MA). Beyond lab works, he’s a passionate internet user with a keen interest in web design and blogging. Furthermore He likes traveling, hanging around with friends and social networking to do in his spare time.

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