Crystallization and Characterization of a Novel Aminopeptidase from Trichosporon cutaneum

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A new N-terminal exopeptidase, L-tryptophan aminopeptidase, was purified and crystallized from the cell-free extract of Trichosporon cutaneum. Enzyme purification was performed by a method involving heat treatment, ammonium sulfate fractionation, chromatographies on DEAE-cellulose and hydroxyapatite columns, and isoelectrofocusing. The enzyme was purified about 1, 600-fold with an overall yield of 23%. The crystallized enzyme was homogeneous on polyacrylamide gel electrophoresis. The molecular weight of the enzyme was determined to be 270, 000 by gel filtration and the enzyme was dissociated into four subunits having a molecular weight of 68, 000 upon sodium dodecylsulfate polyacrylamide gel electrophoresis. L-Tryptophanamide and dipeptides possessing L-tryptophan at the N-terminal moiety were the most favorable substrates. The enzyme activity was absolutely dependent on Mn2+. The enzyme catalyzed the hydrolysis at pH9.0 to 9.5 most rapidly. Other catalytic and physicochemical properties of the enzyme were also examined in some detail.
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