INACTIVATION OF LEUCONOSTOC MESENTEROIDS NRRL B-512F DEXTRANSUCRASE BY SPECIFIC MODIFICATION OF LYSINE RESIDUES WITH PYRIDOXAL-5'-PHOSPHATE

Dextransucrase from Leuconostoc mesenteroides NRRL B-512F was inactiva ted by pyridoxal-5'-phosphate (PLP). The inactivation was reversible i n as much as the loss of enzyme activity was completely reversed by pr olonged dialysis. PLP-modified dextransucrase after reduction with sod ium borohydride showed a characteristic fluorescence emission maximum at 397 nm when excited at 325 nm. The stoichiometric results indicated that four lysine residues are modified by PLP under the experimental conditions. These results established for the first time that lysine r esidues are essential for the activity of dextransucrase.