The effects of long-term and short-term exposure of rats to ethanol on aldehyde
dehydrogenase (ALDH) activity in the liver mitochondria were investigated. The specific
activities of mitochondrial high Km ALDH and low Km ALDH after the prolonged administration
of ethanol were both increased to levels about 2.5 times that of the control group. In
contrast, high Km and low Km ALDH showed maximum activity 12 h after administration
of a single large dose of ethanol, increasing 21 and 4.4 times, respectively, over the level in
the control group. When ethanol was administered for a long time, the two ALDH isoenzyme
levels showed approximately the same increase, while the high Km ALDH level was more
significantly increased than the low Km ALDH level after a single large dose. These results
suggest that the high Km ALDH level of the outer membrane was increased as a result of a
transient increase in the level of acetaldehyde around the liver mitochondria after a single
large dose of ethanol, and that high Km ALDH plays an important role in acetaldehyde
metabolism. However, when ethanol was administered for a long time, the mitochondria
were exposed to low concentrations of acetaldehyde over a long time, leading to an increase
in levels of low and high Km ALDH in the matrix.