title: An abnormal plasma distribution of protein S occurs in functional protein S deficiency.
abstract: Protein S is a natural anticoagulant present in the plasma that serves as a cofactor for activated protein C. Patients deficient in protein S are subject to recurrent venous thrombotic disease. Protein S deficiency differs from other plasma protein deficiencies in that deficient patients often have normal or only mildly reduced levels of protein S in their plasma as detected by conventional immunologic methods but have markedly reduced functional protein S levels. This apparent discrepancy is due to the presence of two forms of protein S in plasma. The protein S is present free and in a complex with C4b-binding protein. The free form is functionally active, whereas the bound form is not. Examination by crossed immunoelectrophoresis of 31 functionally protein S-deficient individuals from seven families reveals that 29 of the 31 have all or most of their protein S complexed to C4b-binding protein with little or no free protein and have correspondingly low levels of protein S functional activity (type I deficiency). Two related protein S-deficient individuals show a different type of distribution with little or no protein S, either bound or free (type II deficiency). The detection and classification of protein S-deficient individuals requires the application of both a functional assay and an assessment of protein S distribution between bound and free forms.
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism; D003169:Complement Inactivator Proteins; D006023:Glycoproteins / Q000172:deficiency* / Q000235:genetics; D006801:Humans; D007122:Immunoelectrophoresis; D010375:Pedigree; D011485:Protein Binding; D017293:Protein S; D013927:Thrombosis / Q000097:blood / Q000235:genetics*
chemical_list: D002352:Carrier Proteins; D003169:Complement Inactivator Proteins; D006023:Glycoproteins; D017293:Protein S