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DIAGNOSTIC ENZYMES AND THEIR CLINICAL IMPORTANCE

Updated on March 15, 2010

Enzymes are substances which catalyse metabolic and biochemical reactions.They are also known as biological catalysts.They enable metabolic and biochemical reactions to occur by lowering the activation energy of such reactions.The following are examples of diagnostic enzymes viz,lactate dehydrogenase(LDH),creatinekinase(CPK),alkaline phosphatase,aspartate aminotransferace(AST) ,alanine aminotransferace(ALT),acid phosphatase,glucose-6-phosphate dehydrogenase and so on.

It is pertinent to note that the rationale for assaying enzyme activities is based on the premise that changes in activities reflect changes that have occurred in aspecific tissue or organ.

Lactate dehydrogenase is an important enzyme involved in glucose metabolism.It is a tetramer(has 2 different subunits).It has five isoenzymes which are designated LDH1(HHHH),LDH2(HHHM),LDH3(HHMM),LDH4(HMMM) and LDH5(MMMM) respectively.Isoenzymes catalyse similar reaction but migrate differently when subjected to electrophoresis.Hence,lactate dehydrogenase activity is found in cardiac muscles and red blood cells( i.e LDH1,LDH2 and LDH4),skeletal muscle(LDH5),Liver (LDH5),kidney and brain (LDH3).Hence,increased LDH activities can be used to detect myocardial infarction,leukaemia,liver cirrhosis,tumours of the central nervous system.

Creatinekinase(CPK) exists as a dimeric enzyme with three isoenzymes CPK1,CPK2, and CPK3.The subunits are designated BB,MB, and MM respectively.Total creatinekinase activity shows an increase following myocardial infarction.It is pertinent to note that it is only when CPK2(i.e MB subunit) contribute more than 6% of the total creatinekinase activity that creatinekinase is implicated in myocardial infarction.

Alkaline phosphatase is an enzyme which transport phosphate groups across cell membranes of organs.It is found in the osteoblasts(bone cells),bile canali ( in the liver),small intestinal epithelium,proximal tubule(kidney) and placenta.Increase in alkaline phosphatase occurs mainly in bone diseases such as Paget disease,Osteogenic sarcoma,liver diseases and bilary tract.

Aspartate aminotransferase (AST) is an enzyme involved in transamination reactions. Transamination reactions produce keto and amino acids simultaneously in tissues where they occur.The assay of serum AST is particularly useful in the diagnosis of myocardial infarction.Elevated AST levels is indicative of damage to the myocardium. Although AST activity is still used in the diagnosis of myocardial infarction,it has been replaced to some extent by the assay of total creatinekinase activity(especially the isoenzyme CPK2).

Serum aminotransferase activities are sensitive indicators of parenchymal liver damage.Both alanine and aspartate aminotransferases have been implicated in infective hepatitis,infectious mononucleosis and hepatocellular damage.Exposure to toxic substances such as carbontetrachloride poisoning ,therapeutic substances such as chlormphenicol, cephalosporins and paracetamol overdose have also resulted in elevated AST and ALT activities.

The serum barely detectable glucose-6-phosphate dehydrogenase activity .An elevated activity is indicative of myocardial infarction .Red blood cells contain 120 – 240 units per 1012 cells. Defeciency of this enzyme can result in hemolytic anaemia through the use of antimalarials such as primaquine, aromatic compounds ,it has also been associated to Favism (resulting from Fava beans consumption.)

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.

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    • profile image

      ERICK KIPNGENO 

      2 years ago

      This article is smart but it is incomplete wonderful job

    • profile image

      vivek Singh 

      2 years ago

      Well n good for concept

    • profile image

      anurag 

      2 years ago

      In complete article

    • profile image

      saikhom mocha singh from manipur 

      4 years ago

      Thanks a lot

    • profile image

      Ahmed Saleh 

      4 years ago

      Thanks a lot ..

      you gave a good idea for this topic

    • profile image

      rasika avatade 

      4 years ago

      Gvng nice n gud infrmation

    • profile image

      drahmed 

      4 years ago

      this is good,

    • profile image

      falak noor 

      4 years ago

      nice article........

    • profile image

      Raziq 

      5 years ago

      good but need more explanation in clinical importance ..

    • profile image

      powell 

      5 years ago

      interesting but incomplete

    • profile image

      INAM KHAN 

      5 years ago

      INTERESTING AND GOOD EFFORT THANKS

    • profile image

      mustafe xuseen xoog 

      6 years ago

      very good but incomplete specially in clinical importance

    • profile image

      Tesfaamlak 

      6 years ago

      great but not completed

    • profile image

      tehseen 

      6 years ago

      good

    • profile image

      faisal iqbal laghari 

      6 years ago

      incomplete article

    • profile image

      amit jaat 

      6 years ago

      it is not complete plz give all enzyme

    • profile image

      vineeth 

      6 years ago

      excellent article. good attempt to constrict a big topic into few important statements. if examples were also there it would have become perfect.

    • profile image

      Sharmila 

      6 years ago

      Nice but want to include clinical importance

    • profile image

      ashwitha 

      7 years ago

      its an incomplete article

    • profile image

      morgan 

      7 years ago

      u are good

    • profile image

      Dr.Devidas Navale 

      7 years ago

      This is a nice article but it is incompleate ... u should include all the enzymes....

    • profile image

      Dr swati Hiwale  

      8 years ago

      this article is good but incomplete .you should inlculde all the diagnostically improtant enzyme .

      swati.bodhey@gmail.com

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