Esaki N, Nakamura T, Tanaka H, Suzuki T, Morino Y, Soda K
Biochemistry. 1981 Jul 21;20(15):4492-6. doi: 10.1021/bi00518a039.
We have investigated selenocysteine (2-amino-3-hydroselenopropionic acid) synthesis with cystathionine beta-synthase (EC 4.2.1.22) and cystathionine gamma-lyase (EC 4.4.1.1) of rat liver. When selenohomocysteine and serine were incubated with cystathionine beta-synthase, selenocystathionine was formed at a rate of 69% of that of cystathionine synthesis. Cystathionine gamma-lyase catalyzed alpha, gamma elimination of selenocystathionine to yield alpha-ketobutyrate, selenocysteine, and NH3. The reaction rate was about 3 times higher than that of cystathionine elimination. Cystathionine beta-synthase, however, did not catalyze direct formation of selenocysteine from serine and H2Se. Thus, selenocysteine is synthesized from selenohomocysteine and cystathionine beta-synthase and cystathionine gamma-lyase reactions. We confirmed this synthetic pathway also with a mixture of both enzymes and with a homogenate of rat liver.
我们研究了大鼠肝脏中胱硫醚β-合酶（EC 4.2.1.22）和胱硫醚γ-裂合酶（EC 4.4.1.1）参与的硒代半胱氨酸（2-氨基-3-氢硒基丙酸）合成过程。当硒代高半胱氨酸和丝氨酸与胱硫醚β-合酶一起温育时，硒代胱硫醚的形成速率为胱硫醚合成速率的69%。胱硫醚γ-裂合酶催化硒代胱硫醚的α,γ消除反应，生成α-酮丁酸、硒代半胱氨酸和NH3。该反应速率比胱硫醚消除反应的速率高约3倍。然而，胱硫醚β-合酶并不催化丝氨酸和H2Se直接生成硒代半胱氨酸。因此，硒代半胱氨酸是通过硒代高半胱氨酸以及胱硫醚β-合酶和胱硫醚γ-裂合酶反应合成的。我们用这两种酶的混合物以及大鼠肝脏匀浆证实了这一合成途径。
