A Novel Putrescine Utilization Pathway Involves γ-Glutamylated Intermediates of Escherichia coli K-12

A novel bacterial putrescine utilization pathway was discovered. Seven genes, the functions of whose products were not known, are involved in this novel pathway. Five of them encode enzymes that catabolize putrescine; one encodes a putrescine importer, and the other encodes a transcriptional regulator. This novel pathway involves six sequential steps as follows: 1) import of putrescine; 2) ATP-dependent γ-glutamylation of putrescine; 3) oxidization of γ-glutamylputrescine; 4) dehydrogenation of γ-glutamyl-γ-aminobutyraldehyde; 5) hydrolysis of the γ-glutamyl linkage of γ-glutamyl-γ-aminobutyrate; and 6) transamination of γ-aminobutyrate to form the final product of this pathway, succinate semialdehyde, which is the precursor of succinate.