Some Catalytic and Molecular Properties of Threonine Deaminase from Bacillus stearothermophilus
1976 年 80 巻 3 号 p. 485-490
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1976 年 80 巻 3 号 p. 485-490
Threonine deaminase [EC 4.2.1.16] was highly purified from Bacillus stearothermophilus. The enzyme exhibited maximum activity at 65° and at pH 9.2-9.6. It was inactivated on dilution and on storage at 4°, but was protected by egg albumin. The enzyme was labile at 65°, but became stable in the presence of egg albumin and isoleucine at pH 7.0. The substrate saturation curve for the enzyme reaction at 40 or 65° was hyperbolic, but in the presence of isoleucine, the curve became sigmoidal (n=2). The enzyme was more sensitive to isoleucine at 40° than at 65°, while valine slightly inhibited the enzyme at both 40 and 65°. Inhibition of the enzyme by isoleucine was antagonized by valine at 40 and 65°. These properties were essentially similar to those of the enzymes from mesophilic and thermophilic bacteria. The enzyme existed in two forms with different molecular sizes, 1.5-5×106 and 2×105 daltons, at pH 7.0 and at temperatures below 40°. The larger component disaggregated into the small one at pH 8.5 or above, at temperatures above 50° or in the presence of isoleucine and valine.
