Solubilization of thiamine triphosphatase from the electric organ of Electrophorus electricus

Abstract

The membrane-associated, anion-regulated thiamine triphosphatase from Electrophorus electricus electric organ can be solubilized by various neutral detergents. Polyoxyethylene ethers are the most effective. Anionic detergents readily inactivate the enzyme. A 6.4-fold increase in specific activity is obtained by successive treatment of crude membranes with octanoyl-N-methylglucamide, which solubilized other proteins, and Lubrol-PX with releases 60% of the thiamine triphosphatase (TTPase) activity. Solubilization by Lubrol-PX rapidly modifies kinetic parameters. The Km, Vmax and pH optimum are decreased. However, the solubilized TTPase may be kept at 0°C for many hours without further change in specific activity. At 35°C, the half-life is still 83 min at pH 5.0, but denaturation becomes rapid at pH ⩾ 7. Solubilization modifies anion effects on TTPase activity. The activating effect of nitrate is nearly lost, while inhibition by sulfate is no longer time-dependent.