Molecular weight estimates of MCP-1 in serum and plasma. Results of size exclusion chromatography for MCP-1 (dashed lines) in (A) EDTA plasma, (B) serum, and (C) heparin plasma. Arrows indicate elution of molecular weight standards, in kDa; solid line indicates absorbance at 280 nm. (A) In EDTA plasma MCP-1 predominantly elutes from the gel filtration column at a molecular weight of approximately 13 500 kDa. The slight shoulder suggests possible dimerization. (B) MCP-1 in serum elutes predominantly as a single peak similar to EDTA plasma. (C) MCP-1 in heparin plasma elutes at a large molecular weight range, suggesting binding of the MCP-1 to the various molecular weight glycosaminoglycans present in unfractionated heparin.