Alternative pathway of complement: nonenzymatic, reversible transition of precursor to active properdin.
A method for the purification of properdin in precursor state (pre-P) has been elaborated. Precursor properdin, in contrast to activated properdin (P), does not initiate the formation of a C3 convertase when added to properdin-depleted serum, rather it requires the presence of an activating substance such as zymosan for expression of its activity. Comparing the activities of pre-P and P it was found that some P preparations contained significant amounts of pre-P because they were fully active only in the presence of zymosan. This observation indicated that P can partly revert to pre-P. Comparison by immunoelectrophoresis and sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed no charge or size differences between pre-P and P. Radiolabeled pre-P, when analyzed after its participation in the reactions of the pathway, displayed an unchanged subunit m.w. of 50,000. Taken together, these results strongly suggest that the transition of pre-P to P is due to a partly reversible change in the conformation of the protein rather than the result of proteolytic cleavage.
D003165:Complement System Proteins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008970:Molecular Weight; D011414:Properdin / Q000032:analysis / Q000302:isolation & purification / Q000378:metabolism*; D011498:Protein Precursors / Q000302:isolation & purification; D013997:Time Factors
D011498:Protein Precursors; D011414:Properdin; D003165:Complement System Proteins