1.1.1.3 -20°C, 0.05 M potassium phosphate buffer, pH 7.5, 1.0 mM EDTA, 2.0 mM dithioerythritol, 5.0 mM L-threonine, 20% v/v glycerol, at least 2 years 1.1.1.3 -20°C, 30 mM potassium phosphate buffer, pH 7.5, 50% v/v glycerol, threonine resistant isozyme at least 2 months stable, threonine sensitive isozyme at least 4 months stable 1.1.1.3 -25°C, 50 mM potassium phosphate buffer, pH 7.2, 15% v/v glycerol, 1 mM EDTA, 1 mM threonine, 14 mM 2-mercaptoethanol 1.1.1.3 -80°C, purified recombinant soluble enzyme, at 3 mg/ml, stable