Purification and Properties of Thermostable Tryptophanase from an Obligately Symbiotic Thermophile, Symbiobactevium thermophilum

Abstract

A thermostable tryptophanase was extracted from a thermophilic bacterium, Symbiobacterium thermophilum strain T, which is obligately symbiotic with the thermophilic Bacillus strain S. The enzyme was purified 21-fold to homogeneity with 19% recovery by a series of chromatographies using anion-exchange, hydroxylapatite, hydrophobic interaction, and MonoQ anion-exchange columns. The molecular weight of the purified enzyme was estimated to be approximately 210,000 by gel filtration, while the molecular weight of its subunit was 46,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, which indicates that the native enzyme is composed of four homologous subunits. The isoelectric point of the enzyme was 4.9. The tryptophanase was stable to heating at 65°C for 20 min and the optimum temperature for the enzyme activity for 20 min reaction was 70°C. The optimum PH was 7.0. The NH2-terminal amino acid sequence of this tryptophanase shows similarity to that of Escherichia coli K-12, despite a great diffe...