Abstract
α1 microglobulin has been isolated from urine of guinea‐pigs with renal damage, induced by sodium chromate. Ultrafiltration, gel chromatography, zone electrophoresis and ion‐exchange chromatography were used for the purification. The protein was shown to be homologous to human α1 microglobulin, as the antiserum against this protein binds guinea‐pig α1 microglobulin. The molecular weight of the protein was 26000 when determined on sodium dodecyl sulfate/polyacrylamide gel electrophoresis, 23000 as determined by gel chromatography in 6 M guanidine hydrochloride, and 24000 estimated from sedimentation and diffusion data. The amino acid content of guinea‐pig α1 microglobulin was similar to that of human α1 microglobulin. The carbohydrate content was 16% and composed of sialic acid, glucosamine and neutral hexoses. The protein was markedly heterogeneous in charge. It was shown to consist of a number of subgroups with different isoelectric points, which showed extreme conservation between the guinea‐pig and human α1 microglobulin. The heterogeneity apparently does not reside in the carbohydrate moiety, since digestion with neuraminidase did not reduce the heterogeneity when tested on agarose gel electrophoresis. Only one band was observed when guinea‐pig α1 microglobulin was subjected to sodium dodecyl sulfate/polyacrylamide gel electrophoresis under reducing conditions. The native protein has a tendency to form dimers. A brown substance is strongly bound to the protein and caused absorbance of light in the ultraviolet and visible regions. Fluorescence was observed in the high‐frequency visible region. α1 microglobulin was present in the serum of guinca‐pigs at a mean concentration of 26.4 mg/ml as determined with radioimmunoassay. The antigenically active α1 microglobulin was eluted as four components of different size when serum of guinea‐pigs was chromatographed on a Sephadex G‐200 column.
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