γ-Glutamyl-γ-aminobutyrate hydrolase in the putrescine utilization pathway of Escherichia coli K-12

gamma-Glutamyl-gamma-aminobutyrate hydrolase (PuuD) was purified and the properties of the enzyme were characterized. The active center of PuuD was identified as Cys-114 by site-directed mutagenesis. The expression of PuuD was induced by putrescine and O-2 (substrates of the Puu pathway), while the addition of succinate or NH4Cl (products of the Puu pathway) to the medium reduced the expression of PuuD. The findings that the puuD-deficient strain accumulated gamma-glutamyl-gamma-aminobutyrate (gamma-Glu-GABA) and could not grow on putrescine as a sole nitrogen source indicate that PuuD is physiologically important as a gamma-Glu-GABA hydrolase.