Isolation and Properties of a Low Molecular Weight β2-Globulin Occurring in Human Biological Fluids

TLDR

β2‑microglobulin, a low‑molecular‑weight β2‑globulin, is present in small amounts in normal human urine, plasma, and cerebrospinal fluid and is elevated in patients with tubular proteinuria. The protein was isolated by sequential ultrafiltration, zone electrophoresis, gel chromatography, and ion‑exchange chromatography. Purification yielded 11–13 % of the 2.8–89 mg of β2‑microglobulin excreted per day, producing a homogeneous 11,600‑Da protein composed of a single 100‑residue polypeptide with a disulfide bond, N‑terminal isoleucine, and no carbohydrate.

Abstract

A low molecular weight β2-globulin (β2-microglobulin) has been purified from urine of patients with tubular proteinurias. The isolation procedure includes ultrafiltration, zone electrophoresis, gel chromatography, and ion exchange chromatography. The yield of purified protein was 11 to 13% of a total amount of 2.8 to 89 mg of β2-microglobulin per 24-hour urine volume. The β2-microglobulin occurs in small quantities in normal human urine, plasma, and cerebrospinal fluid. The purified protein appeared homogeneous in Ouchterlony immunodiffusion, immunoelectrophoresis, starch gel electrophoresis, and ultracentrifugation. The molecular weight found from equilibrium ultracentrifugation was 11,600. Amino acid analyses indicated the presence of 100 residues, giving a calculated molecular weight of 11,815. The protein appears to consist of a single polypeptide chain with 2 half-cystine residues involved in a disulfide bond. Isoleucine was identified as the NH2-terminal residue. The β2-microglobulin is devoid of carbohydrate.