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Isolation and characterization of factor I of the bovine complement system

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  • 1 Department of Microbiology and Immunology, Faculty of Health Sciences, Queen's University, Kingston, ON, Canada K7L 3N6.
  • | 2 Present address is GenVec Incorporated, 12111 Parklawn Dr, Rockville, MD 20852.
  • | 3 Department of Microbiology and Immunology, Faculty of Health Sciences, Queen's University, Kingston, ON, Canada K7L 3N6.

Abstract

Objective—To isolate and characterize factor I of the bovine complement system.

Sample Population—Serum obtained from the blood of beef cattle.

Procedures—Serum samples were fractionated to yield factor I by means of sequential precipitation, ionexchange, and gel-filtration chromatography. The protein was identified throughout the procedure on the basis of its ability to degrade the α'-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 α'-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 and Clinical Relevance—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. (Am J Vet Res 2003;64:989–993)

Abstract

Objective—To isolate and characterize factor I of the bovine complement system.

Sample Population—Serum obtained from the blood of beef cattle.

Procedures—Serum samples were fractionated to yield factor I by means of sequential precipitation, ionexchange, and gel-filtration chromatography. The protein was identified throughout the procedure on the basis of its ability to degrade the α'-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 α'-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 and Clinical Relevance—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. (Am J Vet Res 2003;64:989–993)