Effect of ethanol on peptidases of hamster jejunal brush-border membrane

This study was undertaken to investigate the effect of ethanol on the brush-border activity of the small intestine. Brush-border membrane isolated from hamster jejunum was incubated with L-phenylalanylglycine (Phe-Gly), L-leucylglycine (Leu-Gly), or glycyl-L-tyrosine (Gly-Tyr) in the absence and presence of 1-5% (wt/vol) ethanol, and the L-amino acids liberated were determined. Ethanol was found to depress the hydrolysis of all peptides in a dose-dependent manner. The inhibitory effect of ethanol on the peptidases does not appear to be time dependent. The ethanol-induced inhibition of peptidase activity is completely reversible. Kinetic studies indicate that ethanol caused a decrease in the Vmax of the enzymes responsible for the hydrolysis of the Phe-Gly and Gly-Tyr but did not have any effect on their Km. In the hydrolysis of Leu-Gly, two enzymes were involved, and ethanol depressed the Vmax of both without affecting the Km of either. These findings suggest that ethanol produces conformational changes of the peptidases involved in the hydrolysis of these three dipeptides.