Abstract

Extracellular liquid of the edible fungus Lepista irina was found to effectively degrade β,β-carotene. β-Ionone, β-cyclocitral, dihydroactinidiolide, and 2-hydroxy-2,6,6-trimethylcyclohexanone were formed as volatile breakdown products of β,β-carotene with mycelium-free culture supernatants, whereas β-apo 10'-carotenal was identified as non-volatile degradation product. The key enzyme catalyzing the oxidative cleavage of β,β-carotene was purified with an overall yield of 63% and a purification factor of 43. Biochemical characterization showed a molecular mass of 50.5 kDa and an isoelectric point of 3.75. Fastest β,β-carotene degradation occurred at 34C and pH values between 3.5 and 4. Degenerate oligonucleotides were derived from N-terminal and internal amino acid sequences. By means of PCRbased cDNA-library screening a 1284 bp cDNA was identified which showed great overall similarity to Pleurotus eryngii polyvalent peroxidases. The obtained sequence contains an open reading frame of 1083 nucleotides, encoding a polypeptide of 361 amino acids. A 30 amino acid signal peptide was identified upstream of the Nterminal sequence of the mature enzyme. The L. irina versatile peroxidase represents the first microbial enzyme capable of carotenoid degradation that has been characterized on a molecular level, proving the participation of extracellular enzymes of white rot fungi in biotic carotenoid degradation processes.