Multiple choice

Which one of the following acts as C3 convertase in this particular pathway?

The alternative pathway of complement activation is triggered when a breakdown product of C3 hydrolysis, C3b is deposited on the surface of a microbe. Next step in this pathway is to form C3 convertase which enzymatically breaks down more C3.

  1. C3bBb

  2. C3bBbC3b

  3. C3a

  4. C4b2a

  5. C1
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A Correct answer
Explanation

C3bBb. The microbe-bounded C3b becomes substrate for the binding of another protein called Factor B, which is broken down by a plasma membrane to generate the Bb fragment. This fragment remain attached to C3b and the resulting C3bBb acts as C3 convertase in alternative pathway.

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