Substrate specificity and reaction mechanism of putrescine oxidase

Putrescine oxidase [EC 1.4.3.4] of Micrococcus rubens oxidizes many kinds of synthetic polyamines: triamines (spermidine types), tetramines (spermine types), and N-substituted putrescines. Polyamines possessing terminal 4-aminobutylimino groups in their structures were more active as substrates. Putreanine was oxidized at a rate comparable to that of putrescine, and was converted to 1-pyrroline and beta=alanine. Activities and Km values for polyamines were affected by the substituent attached to the 4-aminobutylimino group of the polyamine, and especially by its methylene chain length. It was also found that two types of oxidation occurred in the oxidation of polyamines by putrescine oxidase. When the moieties attached to the 4-aminobutylimino groups in polyamines were less hydrophobic, these polyamines were oxidized at the secondary amino groups to form 1-pyrroline. Polyamines which contained a hydrophobic substituent attached to the 4-aminobutylimino moiety to form ammonia. N,N'-Bis (4-aminobutyl)-1,3-diaminopropane ([II, 4-3-4]) and N-(4-aminobutyl)-N'-(3-aminopropyl)-1,3-diaminopropane ([II, 4-3-3]) were oxidized to form 1-pyrrolinium salt derivatives as a result of oxidation of the terminal primary amino groups. It was concluded that the essential structure for substrates of putrescine oxidase is a 4-aminobutylimino group (NH2(CH2)4NH-).