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Isozymes / Isoenzymes:

  1. Multiple forms of an enzyme catalyzing the same reaction are called as isoenzymes or isozymes.
  2. They have similar biological action but maybe obtained from different sources.
  3. They have slightly different molecular structure but perform the same catalytic function.
  4. The enzyme Lactate Dehydrogenase (LDH) is present in most animal tissues as five isozymes.
  5. It has to subunits— H(heart) polypeptide and M(muscle) polypeptide. Four units in different combinations, make up the five different molecular forms of LDH.
  6. The five isoenzymes of LDH are:
    HHHH or H4
    HHHM or H3M

    HHMM or H2M2
    MMMM or M4
  7. Isoenzymes differ in their physical and chemical properties.
  8. They provide a clue to the genetic relationships of organisms.
  9. The sequence of amino-acids present in an enzyme is related to the structure of DNA.
  10. Therefore, similarity in isoenzymes is correlated with similarity in DNA structure.
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