title: Isolation and characterization of factor I of the bovine complement system.
abstract: OBJECTIVE
  To isolate and characterize factor I of the bovine complement system. Sample Population-Serum obtained from the blood of beef cattle.
  
  
  METHODS
  Serum samples were fractionated to yield factor I by means of sequential precipitation, ion-exchange, and gel-filtration chromatography. The protein was identified throughout the procedure on the basis of its ability to degrade the alpha'-chain of bovine C3b in the presence of bovine factor H. Electrophoresis in polyacrylamide gels was used to assess the degradation of C3b and determine the molecular weights of factor I and its component polypeptide chains.
  
  
  RESULTS
  Bovine factor I had an apparent molecular weight of 94 kd and consisted of 2 disulfide-bonded polypeptides that had apparent molecular weights of 51 and 42 kd (under reducing conditions). Factor H was required for the factor I cleavage of the alpha'-chain of bovine C3b into iC3b. A similar cofactor effect was provided by trypsinized bovine erythrocytes or erythrocyte ghosts. Bovine properdin was prepared and shown to be a single polypeptide chain of 58 kd in the reduced form.
  
  
  CONCLUSIONS
  Bovine factor I can be purified from serum by a simple 4-step procedure. It is structurally and functionally comparable to factor I of other species, and its purification completes the isolation and characterization of all the soluble components of the bovine alternative complement pathway.
authors.affiliation: Department of Microbiology and Immunology, Faculty of Health Sciences, Queen's University, Kingston, ON, Canada K7L.
authors.forename: Marilyn
authors.initials: M
authors.lastname: Menger
authors.forename: W Peter
authors.initials: WP
authors.lastname: Aston
mesh_terms: D000818:Animals; D002417:Cattle / Q000276:immunology*; D017244:Complement Factor I / Q000737:chemistry* / Q000302:isolation & purification* / Q000378:metabolism; D004912:Erythrocytes; D008970:Molecular Weight
chemical_list: D017244:Complement Factor I