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Acetolactate Synthase (ALS) was partially purified from the yeast and its basic biochemical studies were carried out. Yeast was grown in the minimum media containing 0.5% glucose, 51 mM K2HPO4, 22 mM KH2PO4, 8 mM (NH4)2SO4, 0.4 mM MgSO4 for 18 hours at 37 ℃. The cell was ruptured in the buffer (20 mM phosphate buffer pH 7.0, 0.1 mM TPP, 0.5 mM DTT, 1 μM FAD, and 1 mM MgCl2) following an overnight suspension. The supernatant fraction was collected from 10,000×g and the enzyme was further purified by ammonium sulfate fractionation, DEAE-Sephacel chromatography and leucine-agarose chromatography. The enzyme activity was measured under the various conditions by the function of protein concentration, time, temperature, pH, and substrate. The optimum temperature was found to be 50℃, optimum pH 8.0∼8.5. The kinetic parameters, Km and Vmax were 8.4 mM and 17.9 nmol/mg/min respectively. Stability of the enzyme was studied with ethylene glycol and glycerol added to the enzyme solution. Both ethylene glycol and glycerol improved the enzyme stability up to 50%. The study of feedback inhibition showed that valine was a strong inhibitor while leucine was a weak inhibitor.
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