1.Four multiple molecular forms of NADPH-dependent aldehyde reductase are isolated by ion-exchange and gel chromatography from human brain. Using the same procedure two multiple forms of NADPH-dependent aldehyde reductase are found in rat brain.2. The molecular weight of two of the forms of human brain aldehyde reductase is 40000 and of the other two forms it is 44000.3. Large differences with respect to substrate specificity with a wide range of aliphatic and aromatic aldehydes are observed between the multiple enzyme forms of each species.4. All enzyme forms use NADPH as coenzyme; additionally one enzyme of each species can use NADH as well.5. Classical inhibitors of aldehyde and alcohol dehydrogenase do not affect the activity of the multiple molecular forms of aldehyde reductase from human and rat brain, but psychoactive substances such as barbiturates and chlorpromazine as well as "biogenic" acids are inhibitory. I n view of the possibility that biogenic aldehydes are physiologically active [17,18] and involved in the mechanism of action of psychoactive drugs [19,20] it seemed of interest to characterize the enzymes involved in the metabolism of these aldehydes. This paper reports on the isolation and characterization of aldehydc,reductases from human and rat brain. Preliminary account of the heterogeneity of these enzymes has been presented [21,22].
WATERIALS AND METHODSHuman brains without cortex and cerebellum from both sexes were obtained from legal medical autopsies, death causes being traffic accidents, homicides and cardiovascular diseases. The organs were frozen 6-20 h after death and stored a t -20 "C. Rat brains (RAC rats from the Tierfarm AG, Sisseln, Switzerland) were either frozen 4-6 h after decapitation and stored at -20 "C or used freshly.
A method for the determination of acetaldehyde in human plasma by headspace gas chromatography is described. Chloralhydrate, an inhibitor of aldehyde dehydrogenase, is immediately added to the blood sample to prevent a rapid disappearance of acetaldehyde in the erythrocytes.
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