Miyazaki K, Oshima T
Department of Life Science, Tokyo Institute of Technology, Yokohama, Japan.
FEBS Lett. 1993 Oct 11;332(1-2):37-8. doi: 10.1016/0014-5793(93)80478-d.
The role of Tyr-139, which is thought to be located at the active site of Thermus thermophilus HB8 3-isopropylmalate dehydrogenase, has been investigated by site-specific replacement with phenylalanine. The replacement scarcely affected the Michaelis constant (Km) for 3-isopropylmalate, but caused a 13-fold decrease of that for NAD. The catalytic constant (kcat) showed a 14-fold decrease. Accordingly, the catalytic efficiency (kcat/Km) decreased for 3-isopropylmalate but not for NAD. The results suggest that Tyr-139 is involved in the catalytic function through interaction with 3-isopropylmalate.
人们认为位于嗜热栖热菌HB8 3-异丙基苹果酸脱氢酶活性位点的酪氨酸-139的作用，已通过用苯丙氨酸进行位点特异性置换来研究。该置换对3-异丙基苹果酸的米氏常数（Km）几乎没有影响，但使NAD的米氏常数降低了13倍。催化常数（kcat）降低了14倍。因此，3-异丙基苹果酸的催化效率（kcat/Km）降低，但NAD的催化效率未降低。结果表明，酪氨酸-139通过与3-异丙基苹果酸相互作用参与催化功能。
