Clinical enzymology

Clinical enzymologyUniversity of Babylon College of pharmacySecond semester -biochemistry3rdclass 2014 –2015 By Dr. Abdulhussien M. K. Aljebory

Enzyme activityEnzyme assays usually depend on the measurement the catalytic activity of the enzyme, rather than the concentration of the enzyme protein itself. •One international unitis the amount of enzyme that will convert one micromole of substrate per minute per litreof sample and is abbreviated as U/L. •Katal(catalytic activity)is defined as the number of mole of substrate transformed per second per litreof sample.
Disadvantages of enzyme assaysA major disadvantage in the use of enzymes for the diagnosis of tissue damage is their lack of specificity to a particular tissue or cell type. Many enzymes are common to more than one tissue. •This problem may be obviated to some extent in two ways: •first, different tissues may contain (and thus release when they are damaged) two or more enzymes in different proportions•Second, some enzymes exist in different forms (isoforms)•Individual isoformsare often characteristic of a particular tissue: although they may have similar catalytic activities
Enzymes as Cardiac MarkersCreatinekinase(CK or CPK) Aspartateamino transferase(AST)Lactate dehydrogenase(LDH or LD)Creatine KinaseA cytoplasmicand mitochondriacenzymeTotal CK is %40 sensitive and %80 specific CK-1(BB) : BrainCK-2(MB) :MyocardiumCK-3(MM) :Skeletal muscle ,heartCK-3 has 3 isoforms:CK-31, CK-32and CK-33(posttranslational products)CK-2 has 2 isoforms
Half life :CK-31> CK-32>CK-33, CK-21>CK-22•CK-MB (CK-2) has the most specificity for cardiac muscle (>%85)•CK-MB (CK-2) accounts for only 3-20 % of total CK activity in heart•Normal skeletal muscle contains 1 % CK-2CK-2 is increased insevereskeletal muscle injury (trauma/surgery ),chronic muscle disease (musculardystrophy,polymyositis) and extreme exercise.Reason:Regenerationprocess of muscle (reexpressionof CK-MB genes )In AMI,CK-MB increases at least 4-6 hr.afteronset of chest pain,makesa peak at 12-24 hr.andreturns to baseline level in 2-3 days (t 1/2 is 10-12 hr )