Functional and immunochemical comparison of hepatic UDP-glucuronosyltransferases in a piscine and a mammalian species.
1. The aglycone specificity of hepatic microsomal glucuronidation was compared under uniform conditions in a fish, Pleuronectes platessa and a mammal, Rattus norvegicus, representative of the most primitive and advanced vertebrate classes. 2. Both species exhibited comparable UDP-glucuronosyltransferase (UDPGT) activity towards planar phenolic substrates (1-naphthol, 4-nitrophenol); however, plaice activity towards bulky non-planar substrates such as (-)-morphine was either 200-fold lower, or for an arylacetic acid (RS-2-phenylpropionic acid) and an aryloxyacetic acid (clofibric acid) non-detectable. 3. Conjugation of the endogenous substrates, bilirubin and steroids were 4- to 40-fold lower in the plaice than in the rat. Whilst both species formed diglucuronides of the asymmetrical bilirubin IX alpha, they displayed a reciprocal preference for the initial esterification, conjugation of the C-8 side chain predominating in the rat and of C-12 in the fish. 4. Immunoblot analysis using two polyclonal antisera preparations raised against rat UDPGTs demonstrated the presence of multiple weakly cross-reacting polypeptides in fish microsomes indicative of multiple isoforms and conservation of common structural motifs over more than 350 million years since evolutionary divergence of the mammals.
Clarke
D J
DJ
Department of Biochemical Medicine, University of Dundee, Ninewells Hospital and Medical School, U.K.
Burchell
B
B
George
S G
SG
D000818:Animals; D001663:Bilirubin / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D005432:Flounder; D014453:Glucuronosyltransferase / Q000378:metabolism*; D015151:Immunoblotting; D008862:Microsomes, Liver / Q000201:enzymology*; D009020:Morphine / Q000378:metabolism; D051381:Rats; D013045:Species Specificity; D013379:Substrate Specificity
D009020:Morphine; D014453:Glucuronosyltransferase; D001663:Bilirubin