Mitochondrial aldehyde dehydrogenase from the liver of skipjack tuna Katsuwonus pelamis

Abstract

Aldehyde dehydrogenase (EC 1.2.1.3) in the liver of skipjack tuna ( Katsuwonus pelamis) was extracted from mitochondrial fractions by Triton X-100. The enzyme was purified by ammonium sulfate fractionation, Toyopearl HW-55F, DEAE-Toyopearl 650M, and 5′-AMP-Sepharose 4B column chromatography. The molecular mass of skipjack ALDH (200 kDa) was similar to those of mammals and yeast. The optimum pH was around 10.0 and the enzyme was stable at pH 9.0 and 10.5, but it gradually became unstable when the pH was lower than 7.0. The optimum temperature was around 40°C. The enzyme was stable at 30°C for 60 min, but only 10% of the original activity remained at 40°C for 60 min. The enzyme was activated by Mg 2+ and Mn 2+, and inhibited by Li +, Ba 2+, Cu 2+ and Fe 3+. The K m values for skipjack ALDH were: 15.0 M for acetaldehyde, 32.1 μM for propionaldehyde, 25.9 μM for formaldehyde, 58.7 μM for octylaldehyde, 24.6 μM for benzaldehyde and 40.2 μM for 5-hydroxyindoleacetaldehyde. Skipjack ALDH showed different affinities for substrates than mammalian ALDHs: high affinity against formaldehyde, low affinity against benzaldehyde and medium affinity towards acetaldehyde and propionaldehyde.