Purification and properties of a histidine decarboxylase from Tetragenococcus muriaticus, a halophilic lactic acid bacterium

摘要

Aims: A histidine decarboxylase from Tetragenococcus muriaticus, a halophilic histamine-producing bacterium isolated from Japanese fermented squid liver sauce, was purified to homogeneity, for the first time. Methods and Results: The enzyme was purified 16-fold from cell-free extract by ammonium sulphate precipitation, anion exchange chromatography and hydroxyapatite chromatography. The pure enzyme consisted of two polypeptide chains with molecules mass of 28.8 and 13.4 kDa. The N-terminal amino acid sequence of these polypeptide highly correlated with those of the α- and β-chains of other Gram-positive bacterial histidine decarboxylases. The optimum and stable pH for the enzyme was 4.5-7.0 and 4.0-7.0, respectively. This enzyme did not decarboxylate lysine, arginine, tyrosine, tryptophan and ornithine. The enzyme activity decreased with the addition of NaCl. At pH 4.8, the V_(max) and K_m values were 16.8 μmol histamine min~(-1) mg~(-1) and 0.74 mmol l~(-1), respectively. Conclusions: The very similar physiological properties of this enzyme and almost identical N-terminal amino acid sequences to those from other Gram-positive bacteria indicated that this enzyme may be evolutionally highly conserved among Gram-positive bacteria. Significance and Impact of the Study: Information on this enzyme could be useful for studying the mechanism of histamine accumulation in salted foods. In addition, the N-terminal amino acid sequence can be utilized to design oligonucleotide probes, which may prove valuable in the rapid monitoring of halophilic histamine producers in salted products.