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 inactivated by pyridoxal-5'-phosphate (PLP). The inactivation was reversible in as much as the loss of enzyme activity was completely reversed by prolonged dialysis. PLP-modified dextransucrase after reduction with sodium 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 residues are essential for the activity of dextransucrase.