Isoenzymes

ISOENZYMES


ISOENZYMES (ISOZYMES)

  • Isoenzymes are the physically distinct forms of the same enzyme.
  • Isoenzymes differ from each other structurally, electrophoretically and immunologically.
  • Isoenzymes possess quaternary structure and are made up of two or three different subunit (mutimeric).
  • Isoenzymes catalyze the same reaction and act on same substrate, but with different Km and Vmax values i.e. isozymes have different kinetics.

Plasma Enzymes-

  • Functional plasma enzymes- specific function in the plasma. E.g. Coagulation factors (thrombin), lipoprotein lipase, clotting factors.
  • Non functional enzymes- E.g. alkaline phosphatase, acid phosphatase, gamma glutamyl transpeptidase, LDH, Creatine kinase.

Lactate Dehydrogenase (LDH)

  • LDH with two subunits- H(heart) and M(muscle)
  • It has five isoenzymes.
Name of the isoenzyme Tissue location
LDH-1 Heart muscle
LDH-2 RBC
LDH-3 Brain
LDH-4 Liver and skeletal muscle
LDH-5 Liver and skeletal muscle
  • In MI, LDH1 is raised more than LDH2.
  • Normal LDH pattern on electrophoresis is LDH2 > LDHI > LDH 3 > LDH 4>LDH5
  • Increased in LDH level- pancreatitis.

Creatine Kinase (CK)

  • Three isoenzymes.
  • It is subunit M(myocardium) and B (Brain).
Name of isoenzyme Tissue localisation
CK-1 Brain
CK-2 Heart
CK-3 Skeletal Muscle

Alkaline Phosphatase (ALP)-

Isoenzyme Tissue Location
Alpha-1 ALP Epithelial cells of biliary canaculi
Alpha-2 heat liable ALP Hepatic cells
Alpha-2 heat stable ALP Placenta (Inhibited by Phenylalanine)
Pre beta ALP Osteoblast
Gamma ALP Intestinal cells
Leukocyte ALP Leukocytes
  • Raised activity of alkaline phosphatase is useful in diagnosis of bone and liver pathology.

 Transaminase-

  • Aspartate Transaminase- increase in myocardium.
  • Mitochondrial isoenzyme present in liver.
  • Alanine Transaminase (ALT)-  mainly in liver and entirely in Cytoplasm. 

Protease-

  • Serine Proteasesserine residue at the active site(serine, histidine, aspirate).
  • E.g.- Trypsin, chymotrypsin, elastase (catalytic traid)
  • Inhibited by disopropylphosphofluridate binds covalently to serine residue.
  • Activated in intestine by proteolytic activation.

Carboxyl or acid Proteases-

  • Most important carboxyl proteases is Pepsin.

Exam Important

  1. Isoenzymes differ from each other structurally, electrophoretically and immunologically.
  2. Isoenzymes possess quaternary structure and are made up of two or three different subunit (mutimeric).
  3. Functional plasma enzymes- specific function in the plasma.- E.g. Coagulation factors (thrombin), lipoprotein lipase, clotting factors.
  4. Non functional enzymes  E.g. alkaline phosphatase, acid phosphatase, gamma glutamyl transpeptidase, LDH, Creatine kinase.
  5.  LDH has five isoenzymes.
Name of the isoenzyme Tissue location
LDH-1 Heart muscle
LDH-2 RBC
LDH-3 Brain
LDH-4 Liver and skeletal muscle
LDH-5 Liver and skeletal muscle

 6. In MI, LDH1 is raised more than LDH2.

 7. Creatine Kinase (CK)- Three isoenzymes.

CK-1 Brain
CK-2 Heart

 8. ALP found in liver, bone, kidney, intestinal mucosa and placenta.

9. Serine Proteasesserine residue at the active site(serine, histidine, aspirate).

10. Serine proteases- E.g.- Trypsin, chymotrypsin, elastase (Catalytic triad).

11. Serine proteases activated in intestine by proteolytic activation.

12.  Most important carboxyl proteases is Pepsin.

Don’t Forget to Solve all the previous Year Question asked on ISOENZYMES

Module Below Start Quiz

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