The Linear Dependence of Log(kcat/Km) for Reduction of NAD+ by PhCH2OH on the Distance between Reactants when Catalyzed by Horse Liver Alcohol Dehydrogenase and 203 Single Point Mutants
✍ Scribed by Jia Luo; Kalju Kahn; Thomas C. Bruice
- Publisher
- Elsevier Science
- Year
- 1999
- Tongue
- English
- Weight
- 482 KB
- Volume
- 27
- Category
- Article
- ISSN
- 0045-2068
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✦ Synopsis
Like most dehydrogenases, with horse liver alcohol dehydrogenase (LADH), a bulky amino acid residue (Val 203) is positioned at the face of NAD + distal to substrate alcohol in order to restrict the separation of reactants and to control the stereochemistry. Molecular dynamics simulations of native (Val203) and single-point mutants (Leu203, Ala203, and Gly203) of LADHиPhCH 2 OHиNAD + provide the close contact distances (CCD) between PhCH 2 OH and NAD + reactants. It is found that log(k cat /K m ) is linearly dependent upon CCD. This linear dependence of log(k cat /K m ) upon CCD is expected if hydride transfer is the rate-determining step. Since log(k cat /K m ) has been found to be a linear function of tunneling, ln(k H /k T ) /ln(k D / k T ), it follows that tunneling in LADH has a linear dependence upon CCD.