Different forms of alpha 2u-globulin in male and female rat urine.

alpha 2u-Globulin is usually considered to be present only in male rat urine. This study demonstrates that a very similar protein exists in female rat urine and compares its properties with those of the male form. Isoelectric focusing followed by immunofixation reveals considerable microheterogeneity of alpha 2u-globulin in male and female rat urine. Important sex differences are noted in the banding pattern. The isoelectric point of the major male component (pI approximately equal to 5.3) is considerably higher than that of the major female components (pI approximately equal to 4.6). In addition, the female form of alpha 2u-globulin has a somewhat higher mobility on sodium dodecyl sulphate/polyacrylamide gel electrophoresis than its male counterpart. These sex differences are preserved after purification of alpha 2u-globulin from male and female rat urine by affinity chromatography and enrichment of the major male and female components by ion-exchange chromatography. Immunologically no differences are observed between these purified components and their amino acid composition reveals only minor differences. A slightly higher carbohydrate content is observed in the major female component than in the major male component. Finally evidence is presented that oestrogen treatment suppresses the male forms of alpha 2u-globulin but has no effect on the female forms. The observed differences between the male and female forms and their different hormonal control suggest that they are encoded by different genes.