Johnson J L, Hainline B E, Rajagopalan K V, Arison B H
J Biol Chem. 1984 May 10;259(9):5414-22.
Two stable fluorescent derivatives of molybdopterin have been structurally characterized. Form A is an oxidized pterin with a 6-alkyl substituent. Results of chemical, mass spectral, and NMR studies are consistent with the side chain formulation -C identical to C--CH-OHCH2OPO2-3. Similar studies on the Form B derivative indicate that it is the phosphorylated analog of urothione but lacks the 3-methylthio function. Form B (dephospho) can be synthesized from urothione by desulfuration with Raney nickel and oxidation with SeO2. Chicken liver sulfite oxidase (sulfite:ferricytochrome c oxidoreductase, EC 1.8.2.1) contains one phosphate residue (as molybdopterin) per subunit. The phosphate is noncovalently bound but is not released by trichloroacetic acid at 4 degrees C. The yield of Form A and Form B from sulfite oxidase is 0.50 and 0.27/subunit, respectively. The phosphate ester bond in isolated molybdopterin (Form B) is partially hydrolyzed by 1 N HCl at 100 degrees C (33% in 1 h). The release of inorganic phosphate from sulfite oxidase was more rapid (35% in 10 min) due to the presence of molybdate in the denatured enzyme mixture but slower than expected from a high energy phosphate bond. The presence of molybdopterin in a wide variety of molybdenum- and tungsten-containing enzymes has been demonstrated. Glucose oxidase and the iron and manganese superoxide dismutases are devoid of molybdopterin.
已对钼蝶呤的两种稳定荧光衍生物进行了结构表征。形式A是一种带有6-烷基取代基的氧化蝶呤。化学、质谱和核磁共振研究结果与侧链结构-C≡C--CH-OHCH2OPO2-3一致。对形式B衍生物的类似研究表明，它是尿硫酮的磷酸化类似物，但缺乏3-甲硫基官能团。形式B（去磷酸化）可通过用雷尼镍脱硫并用二氧化硒氧化从尿硫酮合成。鸡肝亚硫酸盐氧化酶（亚硫酸盐：铁细胞色素c氧化还原酶，EC 1.8.2.1）每个亚基含有一个磷酸残基（作为钼蝶呤）。该磷酸是非共价结合的，但在4℃下不会被三氯乙酸释放。从亚硫酸盐氧化酶中得到形式A和形式B的产率分别为0.50和0.27/亚基。分离出的钼蝶呤（形式B）中的磷酸酯键在100℃下被1 N盐酸部分水解（1小时内水解33%）。由于变性酶混合物中存在钼酸盐，亚硫酸盐氧化酶中无机磷酸盐的释放更快（10分钟内释放35%），但比高能磷酸键预期的要慢。已证明多种含钼和含钨的酶中存在钼蝶呤。葡萄糖氧化酶以及铁和锰超氧化物歧化酶不含钼蝶呤。
