Metabolism of biphenyl by Aspergillus toxicarius: induction of hydroxylating activity and accumulation of water-soluble conjugates.
Biphenyl metabolism in Aspergillus toxicarius occurs by successive hydroxylations in the 4- and 4'-positions, followed by conjugation with sulfate to produce 4-hydroxybiphenyl-O-sulfonic acid and 4,4'-dihydroxybiphenyl-O-sulfonic acid. The hydroxylation reactions normally occur only after a prolonged lag period after which the appearance of the monohydroxylated compound precedes the dihydroxylated compound. The accumulation of the monohydroxy compound is transient; therefore, it is an intermediate in the hydroxylating pathway. The onset of hydroxylating activity can be greatly accelerated when the culture is primed with the intermediate or product of the reaction (4-hydroxybiphenyl or 4,4'-dihydroxybiphenyl) at the time of biphenyl addition; a concentration of 0.05 mg 4,4'-dihydroxybiphenyl per ml produces optimal induction. Water-soluble conjugates of 4-hydroxybiphenyl and 4,4'-dihydroxybiphenyl were found in cultures of A. toxicarius grown in the presence of biphenyl plus inducer. The conjugate was shown to be the sulfate ester; no glucuronide or other conjugate species was found in any phase of the transformation. As with hydroxylating activity, the sulfotransferase activity appeared to be induced by the products of biphenyl metabolism.
D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism; D001230:Aspergillus / Q000378:metabolism*; D001713:Biphenyl Compounds / Q000378:metabolism* / Q000494:pharmacology; D004790:Enzyme Induction; D006900:Hydroxylation; D007700:Kinetics
D001189:Aryl Hydrocarbon Hydroxylases; D001713:Biphenyl Compounds; C039430:4-hydroxybiphenyl-O-sulfonic acid; C010574:biphenyl; C039429:4,4'-dihydroxybiphenyl-O-disulfonic acid; C019046:4-phenylphenol; C027439:4,4'-dihydroxybiphenyl