Mass spectrometry identification of circulating alpha-1-B glycoprotein, increased in aged female C57BL/6 mice

In this study, we surveyed the profiles of mouse circulating proteins by 2-dimensional SDS-PAGE in different strains, sexes and ages. Among visible protein spots on 2-D gels with silver-staining, we identified a unique set of 7 seemingly-related proteins whose levels were consistently elevated in older C57BL/6 female mice. This set of 7 proteins was absent in C57BL/6 males or in BALB/c mice of either sex of any age. When C57BL/6 female mice were crossed with BALB/c males, the age-related increase of these proteins became sporadic and not linear in the F1 offspring. All 7 spots of this protein group were picked and subjected to identification by mass spectrometric analysis after tryptic digestion. The results showed that all 7 spots were different isoforms of alpha(1)B-glycoprotein with different degrees of post-translational modifications, such as phosphorylation. These results suggest that alpha(1)B-glycoprotein changes in mice in a sex and age dependent manner.