Carboxylesterase isoenzyme specific deacylation of diacetoxyscirpenol (anguidine).
The deacylation reaction of diacetoxyscirpenol (DAS), a trichothecene mycotoxin, was studied by using five carboxylesterase isoenzymes isolated from mouse liver microsomes. The simultaneous isolation of the five microsomal carboxylesterase isoenzymes was accomplished by chromatofocusing. DAS serves as a unique substrate since both acetyl groups are accessible for hydrolysis, providing an opportunity to investigate the regioselective hydrolysis of DAS with the various isoenzymes. A novel basic carboxylesterase isoenzyme, pI 8.4-8.2, was isolated. This isoenzyme exhibits strict regioselectivity toward DAS hydrolysis; only the acetyl group at C-4, but not that at C-15, is hydrolyzed. Moreover, this is the major isoenzyme responsible for the deacylation of DAS in mouse hepatic microsomes. The rate constant determined for deacylation of DAS at C-4 for this isoenzyme is 130-1000 times greater than that of the other carboxylesterases. This isoenzyme was also the most efficient for the hydrolysis of 4-monoacetoxyscirpenediol with a rate constant 30-100 times greater than that of the other isoenzymes.
Wu
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SE
Department of Applied Biological Sciences, Massachusetts Institute of Technology, Cambridge 02139.
Marletta
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MA
D000818:Animals; D001711:Biotransformation; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D008862:Microsomes, Liver / Q000201:enzymology*; D009183:Mycotoxins / Q000378:metabolism*; D013379:Substrate Specificity; D014255:Trichothecenes / Q000378:metabolism*
D007527:Isoenzymes; D009183:Mycotoxins; D014255:Trichothecenes; D002265:Carboxylic Ester Hydrolases; C001809:diacetoxyscirpenol