Hydrolysis of γ -glutamyl linkages by Fusobacterium nucleatum

Abstract

The cell extracts of two human oral strains (FN2 and FN3) of Fusobacterium nucleatum displayed exceptionally high γ -glutamylpeptidase activity as determined with N-γ - l -glutamyl-2-naphthylamine as substrate. This activity was so dominant that the hydrolysis of other N -aminoacyl-2-naphthylamines progressed at a rate <10% of the former. Two major enzymes (I and II) were partially purified from FN2. I had a molecular weight of 115,000 and did not hydrolyze γ -glutamylcysteinylglycine (glutathione). II had a molecular weight of 70,000 and rapidly liberated only glutamic acid from glutathione. Strain FN3 contained several enzymes hydrolyzing γ -glu-2NA. Direct anion exchange chromatography of FN3 cell extracts separated one enzyme that liberated both glutamic acid and glycine from glutathione, one that was inactive against glutathione (but hydrolyzed γ -glu-2NA), and one that liberated only glutamic acid. Although γ -glu-2NA was a good synthetic substrate, glutathione was hydrolyzed at least 500 times faster by an enzyme present in both strains. These results indicate that the presence of γ -glutamylpeptidase activity is very characteristic of these F. nucleatum strains.