Which of the following statements about C3 is NOT correct?
A)C3 contains an internal thioester bond that participates in covalent linkage to cell surfaces.
B)C3 is the most abundant complement protein in the serum.
C)A proteolytic fragment of C3 is part of both the C3 and C5 convertases.
D)Activated C3 is a serine protease that cleaves C4.
E)C3 in the plasma is spontaneously cleaved into C3b.

Question

Quizplus · Accepted Answer

C3,the most abundant complement protein in plasma,is not a protease.The proteolytic fragment of C3,called C3b,is a component of both classical and alternative pathways C3 convertase,which are proteolytic enzymes.An internal thioester bond in C3 becomes metastable when C3 is proteolytically cleaved and contributes to covalent linkage of C3b to cell surfaces.Spontaneous cleavage of C3 in the plasma,called C3 tickover,generates C3b,which initiates the alternative pathway.

Which of the Following Statements About C3 Is NOT Correct