Distinct but parallel evolutionary patterns between alcohol and aldehyde dehydrogenases: addition of fish/human betaine aldehyde dehydrogenase divergence

Alcohol dehydrogenases (ADHs) of the MDR type (medium-chain dehydrogenases/reductases) have diverged into two evolutionary groups in eukaryotes: a set of 'constant' enzymes (class III) typical of basal enzymes, and a set of 'variable' enzymes (remaining classes) suggesting 'evolving' forms. The variable set has larger overall variability, different segment variability, and variability also in functional segments. Using a major aldehyde dehydrogenase (ALDH) from cod liver and fish ALDHs deduced from the draft genome sequence of Fugu rubripes (Japanese puffer fish), we found that ALDHs form more complex patterns than the ADHs. Nevertheless, ALDHs also group into 'constant' and 'variable' sets, have separate segment variabilities, and distinct functions. Betaine ALDH (class 9 ALDH) is 'constant,' has three segments of variability, all non-functional, and a limited fish/human divergence, reminiscent of the ADH class III pattern. Enzymatic properties of fish betaine ALDH were also determined. Although all ALDH patterns are still not known, overall patterns are related to those of ADH, and group separations may be distinguished. The results can be interpreted functionally, support ALDH isozyme distinctions, and assign properties to the multiplicities of the ADH and ALDH enzymes.     

A hydrogen-bonding network in mammalian sorbitol dehydrogenase stabilizes the tetrameric state and is essential for the catalytic power

Subunit interaction in sorbitol dehydrogenase (SDH) has been studied with in vitro and in silico methods identifying a vital hydrogen-bonding network, which is strictly conserved among mammalian SDH proteins. Mutation of one of the residues in the hydrogen-bonding network, Tyr110Phe, abolished the enzymatic activity and destabilized the protein into tetramers, dimers and monomers as judged from gel filtration experiments at different temperatures compared to only tetramers for the wild-type protein below 307 K. The determined equilibrium constants revealed a large difference in Gibbs energy (8 kJ/mol) for the tetramer stability between wild-type SDH and the mutated form Tyr110Phe SDH. The results focus on a network of coupled hydrogen bonds in wild-type SDH that uphold the protein interface, which is specific and favorable to electrostatic, van der Waals and hydrogen-bond interactions between subunits, interactions that are crucial for the catalytic power of SDH. Received 13 July 2007; received after revision 30 September 2007; accepted 1 October 2007     

Developmental changes of aldehyde dehydrogenase isozymes in human livers: Mitochondrial ALDH2 isozyme is expressed in fetal livers

Summary Previous reports suggested that the major cytosolic aldehyde dehydrogenase (ALDH₁) was present in fetal and infant livers, but the major mitochondrial isozyme (ALDH₂) was absent or severely diminished. Re-examination by means of starch gel electrophoresis followed by enzyme activity staining, and by means of dot blot immuno-hybridization of liver samples with known genotypes of theALDH ₂ locus, indicated that bothALDH ₁ andALDH ₂ genes are expressed in fetal and infant livers. In addition, ALDH₄ isozyme was also observed. The results imply that a fetus with the usual homozygousALDH ₂ ¹ /ALDH ₂ ¹ genotype, but not one with the atypicalALDH ₂ ¹ /ALDH ₂ ² orALDH ₂ ² /ALDH ₂ ² , is capable of detoxifying acetaldehyde transferred from the mother.