Purification and Properties of a New Enzyme, L-Glutamate Oxidase, from Streptomyces sp. X-119-6 Grown on Wheat Bran

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A new flavoprotein enzyme, L-glutamate oxidase, was purified to homogeneity from an aqueous extract of a wheat bran culture of Streptomyces sp. X-119-6. It showed absorption maxima at 273, 385 and 465nm and a shoulder around 490nm, and contained 2 mol of FAD per mol of enzyme. The enzyme had a molecular weight of approximately 140, 000 and consisted of three sizes of subunits with molecular weights of 44, 000, 16, 000 and 9, 000. Balance studies showed that 1 mol of L-glutamate was converted to 1 mol of α-ketoglutarate, ammonia and hydrogen peroxide with the consumption of 1 mol of oxygen. In addition to L-glutamate, L-aspartate was oxidized by the enzyme but only to an extent of 0.6% at pH 7.4; the Michaelis constants were as follows: 0.21 mM for L-glutamate and 29mM for L-aspartate. The isoelectric point was pH 6.2, and the enzyme activity was optimal between pH 7.0 and 8.0. When the enzyme was heated at pH 5.5 for 15 min, the remaining activity was 100% of the original activity level at 65°C, 87% at 75°C and 47% at 85°C.
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