SERUM CONCENTRATIONS OF FREE UBIQUITIN AND MULTIUBIQUITIN CHAINS

Ubiquitin, which can conjugate with cellular proteins, is classified i nto two forms: free ubiquitin and multiubiquitin chains. The latter is active as a signal for degradation of the targeted proteins. We found both forms in human serum and, using two immunoassays, quantitated th em in sera from healthy subjects and patients with some diseases. Beca use of putative leakage of erythrocyte ubiquitin, hemolytic serum and serum obtained after long incubation (> 1-2 h) of blood at room temper ature were excluded. Serum concentrations of multiubiquitin chains and free ubiquitin were substantially higher in rheumatoid arthritis and hemodialysis patients, respectively, than healthy subjects. Additional ly, in acute viral hepatitis, serum multiubiquitin chain concentration s were increased in the acute phase, decreased in the recovery phase, and correlated with alanine and aspartate aminotransferase activities (r = 0.676 and 0.610, P < 0.0001 and < 0.001, respectively). Therefore , serum ubiquitin may have prognostic value.