Putrescine Breakdown in the Yeast Candida boidinii: Subcellular Location of Some of the Enzymes Involved and Properties of Two Acetamidoaldehyde Dehydrogenases

SUMMARY: Two acetamidoaldehyde dehydrogenases were identified in Candida boidinii grown on putrescine as sole nitrogen source with glucose as carbon source. One of them, enzyme A, although present when cells were grown on ammonium or l-lysine, increased in activity when cells were grown on putrescine or spermidine. The other, enzyme B, was absent when the putrescine was replaced by l-lysine or ammonium, but was present if the nitrogen source was spermidine or acetylputrescine. Both dehydrogenases were active with NAD+ or NADP+ as electron acceptor. Apparent K m values for 3-acetamidopropionaldehyde and 4-acetamidobutyr-aldehyde were respectively 0·83 mM and 0·041 mM for enzyme A and 0·077 mM and 0·015 mM for enzyme B. Enzyme A was competitively inhibited by chloral hydrate with a K i of 0·6 mM, whiile enzyme B was unaffected. Both enzymes were slightly (20%) stimulated by 50 mM-KCl. Although both enzymes catalysed the oxidation of a range of aldehyde substrates, and are thus both general aldehyde dehydrogenases, it is suggested that acetamidoaldehyde dehydrogenase B is more probably specifically involved in putrescine degradation. Subcellular fractionation of spheroplast lysates showed that enzyme B was cytosolic, remaining unsedimented at 100000 g, while enzyme A co-sedimented with mitochondrial marker enzymes in a sucrose density gradient. It was also shown that acetamidoalkanoate deacetylase and acetylputrescine oxidase activities, two other key enzymes in the breakdown of putrescine and spermidine, were respectively cytosolic and peroxisomal in their location in the cell.