Tauropine dehydrogenase from the starfish Asterina pectinifera (Echinodermata: Asteroidea): presence of opine production pathway in a deuterostome invertebrate.

Tauropine dehydrogenase (tauropine:NAD oxidoreductase; TaDH) was purified to homogeneity from the body wall of the starfish Asterina pectinifera Müller at Troschel(Echinodermata: Asteroidea) by means of (NH4)2SO4 precipitation followed by column chromatographies in DEAE-cellulose, Sephadex G75, Macro-prep ceramic hydroxyapatite, PBE 94, and Toyopearl HW50S. The enzyme was a monomeric protein of approximately 42000 Da and pI 5.2. The maximum rate of the tauropine biosynthetic reaction was observed at pH 6.0, and that of the tauropine catabolic reaction was at pH 8.7-9.2. Taurine and pyruvate were the preferred substrates. The tauropine catabolic reaction was inhibited by the substrate tauropine: the peak rate was observed at 12.5 mM. Apparent Km values for NADH, taurine, and pyruvate were 0.036 +/- 0.002, 21.3 +/- 1.6, and 0.46 +/- 0.02 mM, respectively, and for tauropine and NAD+ were 2.64 +/- 0.73 and 0.068 +/- 0.005 mM, respectively. The molecular and catalytic properties of the starfish TaDH were basically similar to those of TaDH from other species belonging to the lower invertebrate phyla and the middle phyla of Prostostomia. Tauropine accumulation in vivo during experimental anoxia was also demonstrated. These results gave clear evidence of opine production pathway in deutrostome invertebrate.