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Candida boidinii grows well on spermidine as sole nitrogen source, but poorly on spermine. Cells grown on spermidine, cadaverine, putrescine and 1,3-diaminopropane contained a polyamine oxidase which attacks spermine and spermidine at the secondary amino groups, forming putrescine and a product thought to be 3-aminopropionaldehyde. The enzyme was synthesized before growth began when C. boidinii that had been grown in medium containing glucose + ammonium was transferred to medium in which spermidine replaced ammonium. Other enzymes increasing in specific activity during this adaptation were catalase, benzylamine oxidase and N AD-dependent glutamate dehydrogenase. The polyamine oxidase was purified to 50% homogeneity, but was too unstable to obtain completely pure. It had a pH optimum of 10.0, and could be stabilized by addition of inert protein. It oxidized spermine, spermidine, N 1- acetylspermidine, N-n-butylpropylamine, di-n-butylamine and di-n-hexylamine. It did not oxidize di-n-propylamine, diethylamine or N 1,N 8-diacetylspermidine. Apparent Km values were determined for the active substrates. The enzyme was potently inhibited by quinacrine and by divalent cations. The stoicheiometry of the enzyme reaction was established using di-n-butylamine as substrate. The enzyme has a molecular weight in the range 80000 to 110000. Putrescine (the oxidation product of spermidine) was not oxidized by cell-free extracts, but evidence of aminotransferase activity was found. The oxidation/transamination product of putrescine, 4-aminobutyraldehyde (1-pyrroline), was oxidized by extracts and a scheme is presented by which spermidine could be catabolized. Polyamine oxidase was shown to co-sediment with NAD-dependent glycerol 3-phosphate dehydrogenase and catalase in sucrose gradients after mechanical breakage of spheroplasts, and is thus a peroxisomal enzyme. Polyamine oxidase was present in some other yeasts when grown on spermidine, C. nagoyaensis, Hansenula polymorpha and Trichosporon melibiosaceum, but absent from C. steatolytica, Pichia pastoris and Sporopachydermia cereana. These latter yeasts probably contained an enzyme resembling benzylamine/putrescine oxidase which attacks the primary amino groups of spermidine.
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