title: Fourier transform infrared spectroscopic studies of proton transfer processes and the dissociation of Zn2+-bound water in alcohol dehydrogenases.
abstract: The following complexes were investigated by Fourier transform difference spectroscopy: binary complexes of alcohol dehydrogenases from yeast (YADH) and horse liver (LADH) with nicotinamide adenine dinucleotide (NAD+) and adenosine (5')-diphospho(5)-beta-D-ribose (ADP-Rib); the binary complex of Zn2+-free YADH with NAD+, the ternary complex of LADH with NAD+ and 2,2,2-trifluoroethanol. After addition of NAD+ to YADH and LADH, protonation of the N1 atom of the adenine ring of NAD+ is observed. It is shown that this proton arises from the dissociation of the Zn2+-bound water. The interaction of the Zn2+ ion with water is very strong, since this interaction is not just an electrostatic interaction. If the Zn2+ ions are in a tetrahedral environment, a large covalent contribution also occurs. If ADP-Rib is present instead of NAD+, no protonation of the N1 atom of the adenine ring of ADP-Rib is found, which demonstrates that the positively charged nicotinamide ring favors the conduction of the positive charge. All these results confirm the mechanism of Brändén et al. (1975): the Zn2+-bound water is split and the arising (OH)- deprotonates the alcohol. In the case of the ternary complex of LADH with NAD+ and 2,2,2-trifluoroethanol, we demonstrate that the alcohol is deprotonated and the alcoholate ion is bound directly to the Zn2+ ion. The conduction of the proton from the active site to the N1 atom of adenine occurs via a hydrogen-bonded chain with large proton polarizability due to collective proton motion. The nature and mechanism of this pathway are discussed on the basis of data from previous studies.
authors.affiliation: Institute of Physical Chemistry, University of Munich, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Nadolny
authors.forename: G
authors.initials: G
authors.lastname: Zundel
mesh_terms: D000225:Adenine / Q000737:chemistry; D000246:Adenosine Diphosphate Ribose / Q000737:chemistry; D000426:Alcohol Dehydrogenase / Q000737:chemistry*; D000818:Animals; D006639:Histidine / Q000737:chemistry; D006736:Horses; D006860:Hydrogen Bonding; D008099:Liver / Q000201:enzymology; D009243:NAD / Q000737:chemistry; D011522:Protons; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D017550:Spectroscopy, Fourier Transform Infrared; D014270:Trifluoroethanol / Q000737:chemistry; D014867:Water / Q000737:chemistry; D015032:Zinc / Q000737:chemistry*
chemical_list: D011522:Protons; D014867:Water; D009243:NAD; D000246:Adenosine Diphosphate Ribose; D006639:Histidine; D014270:Trifluoroethanol; D000426:Alcohol Dehydrogenase; D015032:Zinc; D000225:Adenine