Measurement of beta 2-microglobulin in bovine serum and urine by radioimmunoassay.

A radioimmunoassay (RIA) system for quantification of bovine beta 2-microglobulin (beta 2-M) in serum and urine was developed. The protein isolated from bovine colostrum showed a single band in SDS-PAGE, and its molecular weight was approximately 11,600. Amino acid sequences for the first 24 residues and the amino acid composition of the protein were in agreement with those in the bovine beta 2-M of previous research works. In an Ouchterlony test, a single precipitation line was formed between the protein and the antiserum made by the protein. From these results, it was confirmed that the protein isolated from the colostrum was pure bovine beta 2-M. For creation of an RIA calibration curve for urine, a urine void of beta 2-M, as much as possible (beta 2-M-free urine), and a PBS were used as diluents. Intraassay (n = 10) and interassay (n = 3) variances were 1.7-4.6% and 7.1-11.5% in the PBS dilute method, and were 1.4-5.1% and 12.3-13.5% in the beta 2-M-free urine dilute method, respectively. Mean recoveries were 160 +/- 19% (mean +/- SD) and 98.4 +/- 7.9% in PBS and beta-M-free urine, respectively. It was found that the method using the beta 2-M-free urine as a diluent was more accurate than using PBS. The beta 2-M concentrations in serum and urine of healthy Holstein cows measured by this RIA system showed a logarithmic normal distribution for urine and a normal distribution for serum. The mean beta 2-M concentrations were 0.0305(+0.04443)(-0.0210) mg/l (Geometric mean +/- S.D., n = 43) in urine and 2.87 +/- 0.45 mg/l (Arithmetic mean +/- S.D., n = 26) in sera. Further, we could not observe the particular tendency of daily variation in urinary beta 2-M concentrations of healthy cows (Holstein, n = 3 x 2 days).