Rat α1‐microglobulin

Abstract

Rat α₁-microglobulin was isolated from the urine of rats treated with sodium chromate, and was purified by the use of gel chromatography, affinity chromatography on concanavalin-A–Sepharose and ion-exchange chromatography. The protein was heterogeneous in charge, had a tendency to form dimers, and was associated with a brown-coloured chromophore. The size of the protein (25 kDa) was similar to guinea pig α₁-microglobulin but smaller than the human protein, when measured with sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Immunological cross-reaction with human and guinea pig α₁-microglobulin was demonstrated. The concentration of α₁-microglobulin in rat serum was 16.4 mg/l (SD = 8.5 mg/l, n= 13) and rat serum α₁-microglobulin was eluted from a gel chromatography column at two different positions corresponding to monomeric α₁-microglobulin and IgA. The latter α₁-microglobulin activity could be absorbed by anti-IgA serum. Rat α₁-microglobulin and albumin were continuously released into the medium of rat hepatocyte monolayers, and α₁-microglobulin was isolated from the medium by the use of immunoprecipitation with anti-(α₁-microglobulin). Tritiated leucine, added to the medium, was incorporated into the protein, suggesting a de novo synthesis of α₁-microglobulin by the hepatocytes. The size of hepatic α₁-microglobulin was similar to that of purified urinary rat α₁-microglobulin, when determined with sodium dodecyl sulfate/polyacrylamide gel electrophoresis.