Finkelstein J D, Martin J J
J Biol Chem. 1984 Aug 10;259(15):9508-13.
Using an in vitro system which contained enzymes, substrates, and other reactants at concentrations which approximated the in vivo conditions in rat liver, we measured the simultaneous product formation by three enzymes which utilize homocysteine. In the control system, 5-methyltetrahydrofolate homocysteine methyltransferase, betaine homocysteine methyltransferase, and cystathionine beta-synthase accounted for 27, 27, and 46%, respectively, of the homocysteine consumed. Subsequent studies demonstrated that the adaptation from a high protein diet to a low protein diet is achieved by a significant increase in betaine homocysteine methyltransferase, and 83% reduction in cystathionine synthase, and a total decrease of 55% in the consumption of homocysteine. S-Adenosylmethionine, by activating cystathionine synthase, contributes significantly to the regulation of the pathway.
利用一个体外系统，该系统所含的酶、底物和其他反应物的浓度接近大鼠肝脏中的体内条件，我们测量了三种利用同型半胱氨酸的酶同时产生产物的情况。在对照系统中，5-甲基四氢叶酸同型半胱氨酸甲基转移酶、甜菜碱同型半胱氨酸甲基转移酶和胱硫醚β-合酶分别占消耗的同型半胱氨酸的27%、27%和46%。随后的研究表明，从高蛋白饮食转变为低蛋白饮食是通过甜菜碱同型半胱氨酸甲基转移酶显著增加、胱硫醚合酶减少83%以及同型半胱氨酸消耗总量减少55%来实现的。S-腺苷甲硫氨酸通过激活胱硫醚合酶，对该途径的调节有显著作用。
