C3c is derived from iC3b (inactivated C3b) by proteolytic cleavage (Law, S.K.A. and Reid, K.B.M. (1995)). iC3b is created by cleavage of C3b by factor I in the presence of factor H, CR1 or MCP. C3c can be produced by an additional cleavage by factor I if the iC3b is bound to CR1. Factor H cannot serve as a cofactor for this cleavage. C3c can also be produced by the action of trypsin-like proteases on iC3b. If the C3b precursor was attached to a surface, then the iC3b will remain attached to that surface and when iC3b is cleaved the C3c is released into the surrounding solution while the C3dg/C3d fragment remains on that surface. The breakdown of fluid phase C3b is similar, but in this case both C3c and C3dg/C3d are soluble fragments.
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