First fungal aromatic L-amino acid decarboxylase from a paclitaxel-producing Penicillium 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.