Biogenesis of microsomal aldehyde dehydrogenase in rat liver

The biogenesis of a microsomal NAD(P)+-dependent aldehyde dehydrogenase (AlDH) in rat liver was studied using specific antibody raised against the purified enzyme prepared by the method of Nakayasu et al. (Nakayasu, H., Mihara, K., & Sato, R. (1978) Biochem. Biophys. Res. Commun. 83, 697-703). The antibody raised against purified AlDH inhibited the activity of microsome-bound AlDH as effectively as that of the detergent-solubilized enzyme, suggesting that AlDH molecules are present on the outer surface of microsomal vesicles and that a major portion of each molecule, including the active site, is exposed. The cell-free translation of RNA preparations extracted from free and membrane-bound polysomes showed that AlDH was exclusively synthesized on free polysomes. The in vitro synthesized AlDH had the same molecular weight as the authentic enzyme. When a single intravenous injection of [3H]leucine was given to rats, there was no detectable difference in the specific radioactivities of AlDH in rough and smooth microsomes even at the shortest time point, suggesting random incorporation of newly synthesized AlDH molecules into rough and smooth endoplasmic reticulum.