Purification and some properties of factor D of the human properdin system.

Factor D has been purified by gel and ion exchange chromatographies, and by ultrafiltration through different membranes. The final preparation appeared pure in various analytical tests. The molecular weight of human D is 21,500 according to gel chromatography, the isoelectric point was found at pH 7.8. Factor D is an active esterolytic enzyme, it cleaves N-alpha-acetyl-L-lysine methyl ester and N-alpha-acetyl-L-glycyl-L-lysine methyl ester. Both peptide esters inhibit the hydrolytic activation of factor B by D in the presence of cobra venom factor. D is also inhibited by diisopropyl-fluorophosphate and by penylmethyl-sulfonyl-flouride.