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Enzymic Catalysis of the Accumulation of Acetaldehyde From Ethanol in Human Prenatal Cephalic Tissues: Evaluation of the Relative Contributions of CYP2E1, Alcohol Dehydrogenase, and Catalase/Peroxidases
Author(s) -
Person Richard E.,
Chen Hao,
Fantel Alan G.,
Juchau Mont R.
Publication year - 2000
Publication title -
alcoholism: clinical and experimental research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.267
H-Index - 153
eISSN - 1530-0277
pISSN - 0145-6008
DOI - 10.1111/j.1530-0277.2000.tb02114.x
Subject(s) - acetaldehyde , alcohol dehydrogenase , catalase , cyp2e1 , ethanol , peroxidase , chemistry , biochemistry , alcohol , catalysis , aldehyde dehydrogenase , enzyme , microsome
Background: The human prenatal brain is very sensitive to the toxic effects of ethanol, but very little information is available concerning the conversion of ethanol to the highly cytotoxic metabolite, acetaldehyde, in that organ. Thus, experiments were designed to investigate rates of accumulation of acetaldehyde from ethanol in the prenatal human brain. Methods: Prenatal human cephalic tissue homogenates were used as enzyme sources and were compared with analogous preparations of adult rat livers. Generated acetaldehyde was derivatized with cyclohexane‐1,3‐dione to yield fluorescent decahydroacrizine‐1,8‐dione, which was readily separated, detected, and quantitated with HPLC. Results: Detected rates of accumulation were unexpectedly high, even in the absence of added NADPH, NAD + , or H 2 O 2 , which are cofactors/cosubstrates for cytochrome P‐450‐, alcohol dehydrogenase‐ and catalase/peroxidase‐catalyzed reactions, respectively. Without added cofactors/cosubstrates or other components and under linear reaction conditions, rates in human prenatal cephalic preparations were approximately 20% of those observed with analogous preparations of adult rat livers. Cofactor/cosubstrate‐independent reactions were localized in the cytosolic (soluble) fraction and were strongly dependent on molecular oxygen (O 2 ). They were not inhibited substantially by carbon monoxide (CO:O 2 = 80:20 vs N 2 :O 2 = 80:20) or by pyrazole in concentrations up to 10 mM and were only weakly inhibited by azide. Preincubations with excess catalase did not result in decreased activity. Reactions exhibited substrate saturation and heat inactivation indicating enzymic catalysis. Conclusions: Experiments indicated a relatively rapid accumulation of acetaldehyde from ethanol in human prenatal brain tissues and suggested that the observed cofactor/cosubstrate‐independent reactions were largely independent of P‐450 cytochromes, alcohol dehydrogenases, or catalase/peroxidases. Results were consistent with catalysis by an as yet unidentified cytosolic oxidase(s).