FIG. 4.

Biosynthetic pathway of polyamines. In Buchnera, the pathways to synthesize putrescine are absent. The enzymes encoded by the genes are as follows: speA, arginine decarboxylase (EC 4.1.1.19); speB, agmatinase (EC 3.5.3.11); speC, ornithine decarboxylase isozyme (EC 4.1.1.17); speD, S-adenosylmethionine decarboxylase (EC 4.1.1.50); speE, spermidine synthase=putrescine aminopropyl transferase (EC 2.5.1.16); speF, ornithine decarboxylase, inducible (EC 4.1.1.17). Genes present in the Buchnera genome are boxed, while those absent are in parentheses.