COMPLEX-FORMING GLYCOPROTEIN HETEROGENEOUS IN CHARGE AND PRESENT IN HUMAN-PLASMA, URINE, AND CEREBROSPINAL-FLUID

A glycoprotein from the urine of 1 healthy individual was purified by ultrafiltration, ion-exchange chromatography, gel chromatography and immunosorption [using rabbit antiserum]. The protein contained only 1 polypeptide chain with an approximate MW of 31,000 and was associated with a brown color which did not disappear even after total reduction and alkylation of the protein followed by dialysis in 6 M guanidine hydrochloride. The protein appeared homogeneous on sodium dodecyl sulfate-polyacrylamide electrophoresis and gel chromatography. It had only 1 N-terminal amino acid sequence, Gly-Pro, and gave only 1 precipiate with a polyvalent antiserum but was very heterogeneous on agarose gel electrophoresis and on isoelectric focusing. Desialylation of the protein failed to alter this heterogeneity. An electroimmunoassay system was designed to measure the amount of the protein in normal human plasma, urine and CSF where the mean concentrations were about 100, 10 and 0.3 mg/l, respectively. The protein occurred in normal plasma and urine as free monomers and dimers and as complexes with IgA [immunoglobulin A] and albumin.