Enzymatic synthesis of selenocysteine in rat liver.
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.
D000818:Animals; D003541:Cystathionine beta-Synthase / Q000378:metabolism*; D003542:Cystathionine gamma-Lyase / Q000378:metabolism*; D003545:Cysteine / Q000031:analogs & derivatives* / Q000096:biosynthesis; D006836:Hydro-Lyases / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008190:Lyases / Q000378:metabolism*; D013058:Mass Spectrometry; D051381:Rats; D012643:Selenium / Q000096:biosynthesis*; D017279:Selenocysteine
D017279:Selenocysteine; D008190:Lyases; D006836:Hydro-Lyases; D003541:Cystathionine beta-Synthase; D003542:Cystathionine gamma-Lyase; D012643:Selenium; D003545:Cysteine