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Updated: Jun 26, 2026

Mass Spectrometry and Luminogenic-based Approaches to Characterize Phase I Metabolic Competency of In Vitro Cell Cultures
Published on: March 28, 2017
Unconjugated bilirubin inhibits C1 esterase activity
Sandra M Arriaga1, Cecilia L Basiglio, Aldo D Mottino
1Area Bioquímica Clínica y Fisiopatología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Rosario, Argentina. sarriaga@fbioyf.unr.edu.ar
Objective:
To evaluate if unconjugated bilirubin (UB) inhibits C1 esterase activity.
Design And Methods:
Esterase activity was evaluated by C1-mediated hydrolysis of N-acetyl-L-tyrosine ethyl ester, and binding of UB to C1r and C1s was assessed by dot-blot analysis.
Results:
UB inhibited C1 enzymatic activity. C1r, C1s and human serum albumin bound [(14)C]-UB to a similar extent.
Conclusions:
UB inhibits C1 esterase activity, apparently due to a direct pigment-protein interaction. This could explain the inhibitory action of UB on complement activation.
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