Fujioka M, Takata Y
J Biol Chem. 1981 Feb 25;256(4):1631-5.
S-Adenosylhomocysteine hydrolase (EC 3.3.1.1) from rat liver was purified to homogeneity. The enzyme had a molecular weight of 188,000 and was composed of 4 subunits with a molecular weight of 47,000. The isoelectric pH of the enzyme was at 5.7. The Km values for S-adenosyl-L-homocysteine, adenosine, and DL-homocysteine were 15.2 microM, 1.05 microM, and 155 microM, respectively, at pH 7.2 and 25 degrees C. The enzyme showed a fluorescence with an emission maximum at 350 nm when excited at 280 nm. The protein fluorescence was partially quenched on addition of adenosine. The fluorescence quenching as a function of adenosine concentration indicated that the enzyme contained four binding sites for adenosine per molecule. The same data provided a value of 0.63 microM for the dissociation constant of adenosine. The enzyme possessed 4 mol of tightly bound NAD+/mol. The addition of adenosine to the enzyme caused the appearance of a peak at 327 nm in a concentration-dependent manner. The enzyme-bound NAD+ readily formed an adduct with bisulfite with the concomitant loss of enzyme activity. These data suggest that the bound NAD+ is involved in the catalytic mechanism of the enzyme.
大鼠肝脏中的S-腺苷同型半胱氨酸水解酶（EC 3.3.1.1）被纯化至同质。该酶的分子量为188,000，由4个分子量为47,000的亚基组成。酶的等电pH值为5.7。在pH 7.2和25℃下，S-腺苷-L-同型半胱氨酸、腺苷和DL-同型半胱氨酸的Km值分别为15.2 microM、1.05 microM和155 microM。当在280 nm激发时，该酶在350 nm处有最大发射荧光。加入腺苷后，蛋白质荧光部分猝灭。荧光猝灭作为腺苷浓度的函数表明，该酶每分子含有四个腺苷结合位点。相同的数据给出腺苷解离常数的值为0.63 microM。该酶每摩尔含有4摩尔紧密结合的NAD+。向酶中加入腺苷会以浓度依赖的方式在327 nm处出现一个峰。酶结合的NAD+很容易与亚硫酸氢盐形成加合物，同时酶活性丧失。这些数据表明结合的NAD+参与了酶的催化机制。
