ISOENZYMES
-Keshava Pavan K

• Multiple forms of same enzyme catalysing
the same reaction
• Differ in physico-chemical properties

• Amino acid composition
– Electrophoretic separation
• Heat stability
– Placental and intestinal isoenzymes of the 6
isoenzymes of alkaline phosphatase are heat
stable
• Susceptibility to inhibitors
– Acid phosphatase-6 isoenzymes
– Prostate portion is tartarate labile
– Bone portion is urea labile

• Enzyme kinetics
– Km and Vmax differ
• Immunological properties
– Eg,. CKMB estimation
• Different coenzymes
– Isocitrate dehydrogenase
– Mitochondria- NADH
– Cytoplasm- NADPH

• Synthesized from different genes
– Eg,. Salivary and pancreatic amylase are each
formed from different genes
• Oligomeric enzymes
– Lactate dehydrogenase ( polypeptide chains)
– Creatine kinase (4 polypeptide chains)
• Glycoproteins : different amount of
carbohydrate
– Eg,. Alkaline phosphatase – sialic acid ( N Acetyl
neuraminic acid)

• Produced from same locus of gene in
different persons
– G6P dehydrogenase has 400 types.