Stipanuk Martha H
227 Savage Hall, Division of Nutritional Sciences, Cornell University, Ithaca, New York 14853, USA.
Neurochem Res. 2004 Jan;29(1):105-10. doi: 10.1023/b:nere.0000010438.40376.c9.
The first-pass metabolism of dietary sulfur amino acids by the liver and the robust upregulation of hepatic cysteine dioxygenase activity in response to an increase in dietary protein or sulfur amino acid level gives the liver a primary role in the removal of excess cysteine and in the synthesis of taurine. Hepatic taurine synthesis is largely restricted by the low availability of cysteinesulfinate as substrate for cysteinesulfinate decarboxylase, and taurine production is increased when cysteinesulfinate increases in response to an increase in the hepatic cysteine concentration and the associated increase in cysteine dioxygenase activity. The upregulation of cysteine dioxygenase in the presence of cysteine is a consequence of diminished ubiquitination of cysteine dioxygenase and a slower rate of degradation by the 26S proteasome.
肝脏对膳食中含硫氨基酸的首过代谢，以及随着膳食蛋白质或含硫氨基酸水平升高而肝脏半胱氨酸双加氧酶活性的强劲上调，使肝脏在清除过量半胱氨酸和合成牛磺酸方面发挥主要作用。肝脏牛磺酸的合成在很大程度上受限于半胱氨酸亚磺酸盐作为半胱氨酸亚磺酸盐脱羧酶底物的低可用性，当半胱氨酸亚磺酸盐因肝脏半胱氨酸浓度升高及相关的半胱氨酸双加氧酶活性增加而增加时，牛磺酸的生成量会增加。在半胱氨酸存在的情况下，半胱氨酸双加氧酶的上调是由于半胱氨酸双加氧酶泛素化减少以及26S蛋白酶体降解速率减慢所致。
