Detection of ubiquitin in serum and urine.

(A) Ubiquitin serum and urine concentrations in healthy volunteers and critically ill patients. The boxes extend from the 25th to 75th percentile; the horizontal line shows the median. Error bars show the range of data. Data are measurements of ubiquitin concentrations in serum samples from 35 healthy uninjured donors, 23 severely injured blunt trauma patients on the day of admission, and 24 patients with sepsis. Ubiquitin urine concentrations were determined in specimens from 19 sepsis patients and 10 healthy individuals. *P < .05 versus concentrations in specimens from healthy volunteers. (B) Detection of free ubiquitin in serum specimen by immunoblotting. Serum proteins were separated by SDS-PAGE, transferred to PVDF membranes, and probed for ubiquitin with antiubiquitin AS (1:200). Lane 1, healthy donors' serum (15 μg); lanes 2-5, patients' serum (lane 2, 10 μg; lane 3, 15 μg; lane 4, 20 μg; lane 5, 25 μg); lane 6, ubiquitin (Ub; 10 ng). (C) Detection of free ubiquitin in urine specimen (10 μL) by immunoblotting. Lane 1, ubiquitin (Ub; 5 ng); lane 2, healthy donors' specimen; lanes 3 and 4, patients' specimens.