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→Alternative Pathway
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To begin the cascade C3b binds to a surface that stabilises the C3b. C3b can bind to any surface as it has a binding site that anchors it to any surface, however it is only the surfaces of certain activators that can stabilise the otherwise short-lived C3b in the absence of antibody. These include Gram-negative bacteria, yeasts and fungi. When the active C3b is bound to particle surfaces, it is protected from inactivation by another complement component, properdin. Therefore, having the C3b bound to a surface enables the C3b to become active for longer. The C3b can then bind Factor B producing the complex C3bB. While in this complex, Factor B can become a substrate for the plasma enzyme known as Factor D. Factor D then splits a small peptide (the Ba peptide) from Factor B to generate the '''C3 convertase (althernative pathway)''' made of C3b¯Bb.
To begin the cascade C3b binds to a surface that stabilises the C3b. C3b can bind to any surface as it has a binding site that anchors it to any surface, however it is only the surfaces of certain activators that can stabilise the otherwise short-lived C3b in the absence of antibody. These include Gram-negative bacteria, yeasts and fungi. When the active C3b is bound to particle surfaces, it is protected from inactivation by another complement component, properdin. Therefore, having the C3b bound to a surface enables the C3b to become active for longer. The C3b can then bind Factor B producing the complex C3bB. While in this complex, Factor B can become a substrate for the plasma enzyme known as Factor D. Factor D then splits a small peptide (the Ba peptide) from Factor B to generate the '''C3 convertase (alternative pathway)''' made of C3b¯Bb.
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