Bellahsene Z, Dhondt J L, Farriaux J P
Biochem J. 1984 Jan 1;217(1):59-65. doi: 10.1042/bj2170059.
The GTP cyclohydrolase activity of rat tissues has been studied by means of the measurement of formic acid release and neopterin synthesis from GTP. After gel filtration of a 45%-satd.-(NH4)2SO4 fraction of liver homogenates, three enzyme fractions were separated and named A1, A2 and A3 according to the order of their elution. Fractions A1 and A3 displayed an 8-formyl-GTP deformylase activity; no proof of cyclized product has yet been established. This activity was heat-labile and required Mg2+ for maximal activity. Fraction A2 displayed a 'neopterin-synthetase' activity, with dihydroneopterin triphosphate and formic acid formed in stochiometric amounts. Fraction A1 isolated from heat-treated homogenates also produced dihydroneopterin triphosphate. Neopterin synthetase activity in fractions A1 and A2 was heat-resistant and inhibited by Mg2+. In liver the A2 fraction represented 70-75% of the neopterin synthetase capacity and was inhibited by reduced pterines (sepiapterin, dihydrobiopterin and tetrahydrobiopterin) and to a lesser extent by reduced forms of folic acid. In kidney and brain, fraction A1 and A3 GTP 8-formylhydrolase activities were found in significant amounts, in contrast with the neopterin synthetase activity, which was low and appeared to be confined to the A1 fraction.
通过测量甲酸释放量以及从鸟苷三磷酸（GTP）合成新蝶呤的量，对大鼠组织中的GTP环化水解酶活性进行了研究。对肝脏匀浆45%饱和度硫酸铵分级分离后的组分进行凝胶过滤后，分离出三个酶组分，按照洗脱顺序分别命名为A1、A2和A3。组分A1和A3表现出8-甲酰基-GTP脱甲酰酶活性；尚未证实有环化产物。该活性对热不稳定，最大活性需要镁离子。组分A2表现出“新蝶呤合成酶”活性，以化学计量产生三磷酸二氢新蝶呤和甲酸。从热处理匀浆中分离出的组分A1也产生三磷酸二氢新蝶呤。组分A1和A2中的新蝶呤合成酶活性耐热且受镁离子抑制。在肝脏中，A2组分占新蝶呤合成酶总活性的70%-75%，并受到还原型蝶呤（异翼蝶呤、二氢生物蝶呤和四氢生物蝶呤）的抑制，在较小程度上也受到还原型叶酸的抑制。在肾脏和大脑中，发现组分A1和A3有大量的GTP 8-甲酰水解酶活性，与之形成对比的是，新蝶呤合成酶活性较低，似乎仅限于A1组分。
