CHEMICAL MODIFICATION OF DEXTRANSUCRASE FROM LEUCONOSTOC-MESENTEROIDES NRRL B-512F BY PYRIDOXAL 5'-PHOSPHATE - EVIDENCE FOR THE PRESENCE OFAN ESSENTIAL LYSINE RESIDUE AT THE ACTIVE-SITE

The treatment of Leuconostoc mesenteroides NRRL B-512F dextransucrase with lysine specific reagent, pyridoxal 5'-phosphate (PLP) at pH 5.2 a nd 30 degrees C resulted in the loss of enzyme activity. The inactivat ion by PLP could be reversed completely by dilution or dialysis. Sucro se as well as acceptor substrates, glucose and dextran protected the e nzyme against inactivation by PLP. A statistical, kinetic analysis of the inactivation by PLP showed that one lysine residue is essential fo r the enzyme activity. All these results showed that one lysine residu e present at the active is essential for the activity of dextransucras e.