Free protein S levels are elevated in familial C4b-binding protein deficiency.
In plasma, 40% of the protein S is free and functions as a cofactor for the anticoagulant effects of activated protein C. The remaining 60% of protein S is complexed to C4b-binding protein and is functionally inactive. A family with hereditary C4b binding protein deficiency has been identified with C4b-binding protein levels in an affected father and daughter of 37 micrograms/mL and 23 micrograms/mL, respectively; these values are significantly below the normal range for this protein of 180 micrograms/mL +/- 44 micrograms/mL (mean +/- 2 SD). The total protein S (free + bound) is normal in these individuals (23.2 micrograms/mL and 17.8 micrograms/mL, respectively; normal 19.1 micrograms/mL +/- 6.0 micrograms/mL). The free protein S levels are markedly increased at 22.5 micrograms/mL and 17.4 micrograms/mL, respectively (normal 5.9 micrograms/mL +/- 2.4 micrograms/mL). This experiment of nature shows that total protein S levels in plasma are not affected by the absence of C4b-binding protein and that chronic elevation of free protein S is not associated with increased hemorrhagic tendencies.
Comp
P C
PC
Department of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City 73104.
Forristall
J
J
West
C D
CD
Trapp
R G
RG
D000328:Adult; D002352:Carrier Proteins / Q000097:blood*; D003169:Complement Inactivator Proteins; D005192:Family Health; D005260:Female; D006023:Glycoproteins / Q000097:blood*; D006801:Humans; D007123:Immunoelectrophoresis, Two-Dimensional; D008297:Male; D010375:Pedigree; D011488:Protein Deficiency / Q000097:blood* / Q000235:genetics; D017293:Protein S
D002352:Carrier Proteins; D003169:Complement Inactivator Proteins; D006023:Glycoproteins; D017293:Protein S