DIFFEKENTIAL CALCIUM－BINDING ABILITY OF FREE AND BOUND PROTEINS－SUGGESTIONOFAN0VELPROTEINS／C4B－BINDINGPKOTE

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DIFFEKENTIAL CALCIUM-BINDING ABILITY OFFREE AND BOUND PROTEIN S-SUGGESTION OF AN0VEL PROTEIN S/C4B-BINDING PKOTEIN-BIND-ING FACTOR IN HUMAN PLASMA

The phenotype and calcium-binding ability of protein S(PS)in human plasma andserum were analyzed by crossed immunoelectrophoresis(CIE) and ion exchange chromatography. Whenhuman plasma and serum were applied to CIE in the presence of EDTA ,two PS peaks were detected:free PS appeared as a faster-migrating peak and PS-C4b binding protein complex(PS/C4BP ) ap-peared as a slower-migrating peak. However,when the CIE was performed in the presence of calcium,three PS phenotypes were detected: free PS appeared as a middle-migrating peak and the bound PS ap-peared as a faster-migrating peak. Human plasma and serum was applied to anion exchange chro-matography and the proteins were eluted with NaCl or CaCl2 gradient buffer. When eluted with NaCl,free PS appeared at 0.4 M NaCl and bound PS appeared at 0.25 M NaCl for plasma,but for serum,free and bound PS appeared together at 0.4 M NaCl.When eluted with CaCl2,the free PS appeared at30 mM CaCl2,bound PS appeared at 46 mM CaCl2and C4BPappeared at 5O mM CaCl2. Differentialelectrophoretic mobilities and chromatography elut ion profiles of free and bound PS in the presence andabsence of calcium suggest that(i)free PS has higher calcium-binding affinity than bound one has;(ii)a novel factor may exist in human serum,which binds to PS/C4BP in the presence of calcium.