Purification of native properdin by reversed affinity chromatography and its activation by proteolytic enzymes

A highly purified preparation of human properdin (P) has been obtained in a simple two-step procedure utilizing reversed application of the technique of affinity chromatography. The method involved precipitation of properdin from human serum and subsequent passage through an immunoadsorbent column of Sepharose anti-RP globulin which bound the contaminating proteins. The immunochemical properties of the isolated properdin (P) was found to be different from those of activated properdin (P). P was shown to be a 6.1S, beta2 globulin with a mean subunit m.w. of 57,900. P on the other hand was a 5.1S protein with gamma2 mobility and a subunit m.w. of 53,000 daltons. Double diffusion analysis using anti-P revealed a reaction of identity between P and P. However, when the reaction was developed with anti-P, a reaction of partial identity was obtained and the precipitin line of P was seen to spur over the line developed with P. Mild treatment with plasmin or trypsin converted P to P. Unlike P, P was ineffective in triggering the activation of the Properdin System in RP unless trace amounts of zymosan were added. Under these conditions P was found to be converted to P. The results indicate that properdin is present in fresh serum in a precursor form and its activation to P involves a limited proteolytic cleavage of the molecule.