Unconjugated bilirubin inhibits C1 esterase activity.
OBJECTIVE
To evaluate if unconjugated bilirubin (UB) inhibits C1 esterase activity.


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.
Arriaga
Sandra M
SM
Area Bioquímica Clínica y Fisiopatología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Rosario, Argentina. sarriaga@fbioyf.unr.edu.ar
Basiglio
Cecilia L
CL
Mottino
Aldo D
AD
Almará
Adriana M
AM
D001663:Bilirubin / Q000737:chemistry* / Q000494:pharmacology*; D003173:Complement C1s / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D015151:Immunoblotting
D003173:Complement C1s; D001663:Bilirubin