Characterization of thioltransferase from Kale

초록

Thioltransferase, also known as glutaredoxin, is an enzyme that catalyzes the reduction of a variety of disulfides, including protein disulfides, in the presence of reduced glutathione. Thioltransferase was purified from kale through ammonium sulfate fractionation, DE-52 ion-exchange chromatography, Sephadex G-75 gel filtration, and Q-Sepharose ion-exchange chromatography. Its molecular size was estimated to be about 31,000 daltons on SDS-PAGE. The purified enzyme has an optimum pH of about 8.0 with 2-hydroxyethyl disulfide as a substrate. The enzyme also utilizes L-sulfocysteine, L-cystine, bovine serum albumin, and insulin as substrates in the presence of GSH. The enzyme has K<inf>m</inf> values of 0.24-0.67 mM for these substrates. The enzyme was partly inactivated after heating at 80°C or higher temperature for 30 min. The enzyme was stimulated by various thiol compounds such as reduced glutathione, dithiothreitol, L-cysteine, and β-mercaptoethanol. This is a second example of a plant thioltransferase which was purified and characterized.

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