Tauropine dehydrogenase from the sandworm Arabella iricolor (Polychaeta: Errantia): Purification and characterization

This is thr first report of the purification of tauropine dehydrogenase (NAD: tauropine oxidoreductase) from a polychaete worm. In the sandworm Arabella iridolor Montagu (Polychaeta: Errantia), two forms of TaDH were detected: major component (pI = 7.5) and minor one (pI = 6.4). The major TaDH component was purified to homogeneity by means of (NH4)(2)SO4 precipitation, anion-exchange, affinity, chromatofocusing and hydrophobic chromatography, and characterized. From the molecular mass of 43.7 kDa obtained by rapid gel-filtration and that of 43.5 kDa by SDS-PAGE, the sandworm enzyme appeared to he a monomeric protein. Maximum rates of reduction of pyruvate and oxidation of tauropine were observed at pH 7.0 and 8.5, respectively. Pyruvate and taurine were preferred substrate for thr enzyme. Apparent K-m values determined using constant co-substrate concentrations were: 35.7 mM, 0.34 mM, and 0.036 mM for taurine, pyruvate: and NADH, respectively, in the tauropine synthesizing reaction; and 4.8 mM and 0.051 mM for tauropine and NAD', respectively, in the tauropine oxidizing reaction. The tauropine synthesizing reaction was subject to substrate: inhibition hy pyruvate: maximum rate was observed at 2.5-3.0 mM (inhibitory range of pyruvate concentration producing half-maximal rate was 26.8 mM).