First fungal aromatic L-amino acid decarboxylase from a paclitaxel-producingPenicillium raistrickii

This is the first description of a fungal aromatic L-amino acid decarboxylase. It was isolated from a paclitaxel producing Penicillium, raistrickii isolate H10BA2, isolated from Taxus brevifolia phloem. The enzyme was purified to homogeneity as demonstrated by the presence of one protein band (125 000 ± 3000 Da) in a silver stained SDS-PAGE gel, and yielded a monomer under reducing conditions. Optimum pH for catalysis by this enzyme was pH 5.0 to 5.6 at 36 C. The enzyme had a broad substrate specificity utilizing L-tryptophan (Km = 49 μM), L-tyrosine (Km = 1064 μM), and L-phenylalanine (Km = 99 μM), as well as o-fluorophenylalanine, and p-fluorophenylalanine. Enzyme activity was not detected with either D-phenylalanine, L-5-hydroxytryptophan or L-histidine as substrate. The protein had a pI of 6.2-6.4, as determined by enzyme activity in this pH range in an isoelectric focusing gel. This fungal aromatic amino acid decarboxylase was not inhibited by the suicide inhibitors L-α-fluoromethyltyrosine and L-α-fluoromethyl(3,4-dihydroxyphenyl)alanine. This enzyme activity was not detectable in P. raistrickii ATCC #46878, isolated from Eucalyptus sp. leaves. This enzyme was compared to previously described aromatic amino acid decarboxylases, and its possible function in secondary metabolism is discussed.