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 decarboxyla se. It was isolated from a paclitaxel producing Penicillium raistrickii iso late H10BA2, isolated from Taxus brevifolia phloem. The enzyme was purified to homogeneity as demonstrated by the presence of one protein band (125 00 0 +/- 3000 Da) in a silver stained SDS-PAGE gel, and yielded a monomer unde r reducing conditions. Optimum pH for catalysis by this enzyme was pH 5.0 t o 5.6 at 36 C. The enzyme had a broad substrate specificity utilizing L-try ptophan (Km = 49 mu M), L-tyrosine (Km = 1064 mu M), and L-phenylalanine (K m = 99 mu M), as well as o-fluorophenylalanine, and p-fluorophenylalanine. Enzyme activity was not detected with either D-phenylalanine, L-5-hydroxytr yptophan or L-histidine as substrate. The protein had a pI of 6.2-6.4, as d etermined by enzyme activity in this PH range in an isoelectric focusing ge l. This fungal aromatic amino acid decarboxylase was not inhibited by the s uicide inhibitors L-alpha-fluoromethyltyrosine and L-alpha-fluoromethyl (3, 4-dihydroxyphenyl) alanine. This enzyme activity was not detectable in P. r aistrickii ATCC #46878, isolated from Eucalyptus sp. leaves. This enzyme wa s compared to previously described aromatic amino acid decarboxylases, and its possible function in secondary metabolism is discussed.