MODEL MOLECULES FOR THE ACTIVE-CENTER OF ALCOHOLDEHYDROGENASES - AN FT-IR STUDY

We synthesized a triamide of Kemp's acid with two cysteine groups and one histidine group (compound 1), and a triamide of 1,3,5-pentane tric arboxylic acid with tyrosine, histidine, and arginine molecules (compo und 2). From compound 1 we obtained the hydrated Zn2+ complex, compoun d 3. The FT-IR spectra of various complexes of compounds 1-3 with NAD( +) show no IR continua and hence, no hydrogen-bonded chains with proto n polarizability are present. In the case of the complex (compounds 2 and 3 and NAD(+)) an intense continuum demonstrates that a hydrogen-bo nded chain is formed with large proton polarizability due to collectiv e proton motion. This proton pathway is discussed. The O atom of the n icotinamide group of NAD(+) is a strong hydrogen bond acceptor. This r esult is discussed with regard to the catalytic mechanism. (C) 1997 Ac ademic Press.