A MODEL SYSTEM FOR THE HYDROGEN-BONDED CHAIN IN THE ACTIVE-CENTER OF THE MALTODEXTRINPHOSPHORYLASE - A FTIR STUDY

Model systems for the hydrogen bonded chain in the active centre of ma ltodextrinphosphorylase are synthesized and studied by FTIR spectrosco py. A hydrogen bonded system between an amine, the phosphate group of pyridoxalphosphate (PLP) and the phosphate group of glucose-1-phosphor ic acid (GLC-1-P) causes an intense continuum in the IR spectrum, indi cating that this hydrogen bonded chain shows large proton polarizabili ty owing to collective proton tunnelling in multi-minima proton potent ials. If the sodium salt of stearic acid is added to this hydrogen bon ded chain, a very intense continuum is again observed. In addition, th e carboxylate group of the stearic acid sodium salt becomes partially protonated since a v(C=O) vibration of the carboxyl group arises at 16 78 cm(-1). The protons are located in this additional part of the chai n.