. "The chemical reactions and pathways resulting in the formation of putrescine, 1,4-diaminobutane; putrescine can be synthesized from arginine or ornithine and is the metabolic precursor of spermidine and spermine." . . . "putrescine biosynthetic process" . "putrescine anabolism" . "putrescine biosynthesis" . "putrescine formation" . "putrescine synthesis" . . . . .