Involved in the putrescine catabolism. Catalyzes the transfer of the amino group from putrescine to pyruvate to yield 4-aminobutanal and alanine. putrescine + pyruvate = 4-aminobutanal + L-alanine Amine and polyamine degradation; putrescine degradation; 4-aminobutanal from putrescine (transaminase route). By putrescine and agmatine. Also regulated by the global CbrA/CbrB two-component system. Cells lacking this gene are unable to utilize putrescine as the sole source of carbon and nitrogen. Belongs to the class-III pyridoxal-phosphate-dependent aminotransferase family.