Liang Tang, Glenn Frank
Identification and Characterization of an Aromatic Amino Acid Decarboxylase from the Filarial Nematode, Dirofilaria immitis
A novel secreted aromatic amino acid decarboxylase-like molecule was identified in the excretory/secretory
products of L3/L4 larvae as well as in an extract
of adult Dirofilaria immitis. The secretion of the
enzyme was developmentally regulated. Peak enzyme
activities were detected in the culture medium
before and after the molting of L3 larvae in vitro. The
enzyme was purified from D. immitis adult extracts
and the excretory/secretory products of L3/L4 larvae
using different chromatographic methods followed
by isoelectric focusing and SDS-PAGE. The enzyme
has a molecular mass of 48 kDa and a pI of 5.6, and
shows a specific enzymatic activity towards the aromatic
amino acid substrates phenylalanine, tyrosine
and tryptophan. The enzymes activity did not show
an absolute requirement for exogenous pyridoxal-5-phosphate. However, addition of pyridoxal-5-phosphate
at 5 ?M in the reaction increased the enzyme
activity greatly. The enzyme had the ability to catalyze
the formation of dopamine from L-dopa. Studies on
the effects of inhibitors on the enzyme activity
showed that the enzyme was sensitive to Pefabloc
and p-chloromercuribenzoic acid, but not to diisopropyl
flurophosphate. The Km values of the enzyme for H-Phe-AMC, H-Tyr-AMC and H-Trp-AMC were calculated to be 32.1 ?M, 35.1 ?M and 29.1 ?M, respectively.
Biological Chemistry, Walter de Gruyter
Print ISSN: 1431-6730
Volume: 382, 02/2001
Pages: 115 - 122
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