title: The autoactivation of rabbit Hageman factor.
abstract: Proteolytic cleavage and activation of isolated, single chain, zymogen Hageman factor was observed in the presence of kaolin alone. The rate of cleavage of kaolin-bound Hageman factor was enhanced 50-fold by the presence of prekallikrein and high molecular weight kininogen. The two-chain 82,000 dalton form of activated Hageman factor (alpha-HF(a)) also cleaved kaolin- bound single-chain Hageman factor in a dose-dependent manner, yielding fragments of 28,000 and, 50,000 dahons under reducing conditions. Cleavage of kaolin-bound single-chain Hageman factor was not inhibited by preincubation with diisopropylfluorophosphate (12 mM) for 10 min, but long-term incubation of Hageman factor with diisopropylfluorophosphate (up to 48 h) resulted in inhibition of cleavage of kaolin-bound Hageman factor to an extent proportional to the inhibition of procoagulant Hageman factor activity. Hageman factor cleavage was maximal when the kaolin concentration was {approximately} 10-fold greater than the Hageman factor concentration (wt:wt), and was partially inhibited by high molecular weight kininogen. Kaolin-bound Hageman factor cleaved clotting factor XI in an amount which correlated with the extent of cleavage of the Hageman factor. These findings are compatible with the concept that single-chain Hageman factor and alpha- HF(a), are both capable of cleaving and activating kaolin-bound Hageman factor and that a close molecular association of kaolin-bound Hageman factor molecules is required for this reaction.
mesh_terms: D000818:Animals; D001778:Blood Coagulation Disorders / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005174:Factor XII / Q000302:isolation & purification / Q000378:metabolism*; D007531:Isoflurophate / Q000378:metabolism*; D007610:Kallikreins; D007616:Kaolin / Q000378:metabolism; D007704:Kininogens / Q000378:metabolism; D011288:Prekallikrein; D011817:Rabbits; D014316:Tritium
chemical_list: D007704:Kininogens; D014316:Tritium; D007531:Isoflurophate; D007616:Kaolin; D005174:Factor XII; D011288:Prekallikrein; D007610:Kallikreins