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Non-competitive Inhibition

  1. In this type of inhibition, the inhibitor is not structurally similar to the substrate molecule so the inhibitor does not compete with the substrate for binding to the active site of the enzyme.
  2. It binds at a site other than the active site on the surface of the enzyme.
  3. This binding alters the physical structure of the enzyme.
  4. The inhibitor does not interfere with enzyme-substrate binding.
  5. But, catalysis is prevented, due to distortion in the enzyme conformation.
  6. Non-competitive inhibition cannot be reversed by increasing the substrate concentration.

Examples:

  • Cyanides inhibiting the activity of cytochrome oxidase which is essential for nearly all mammalian cells. This results in cyanide poisoning.
  • Heavy metal ions ( Hg2+, Ag+, Pb2+) can non-competitively inhibit the enzymes by binding to the cysteine sulfhydryl groups
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