Rat α1‐microglobulin

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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.