Maras B, Stover P, Valiante S, Barra D, Schirch V
Dipartimento di Scienze Biochimiche, Università La Sapienza, Rome, Italy.
J Biol Chem. 1994 Jul 15;269(28):18429-33.
The primary sequence of 5,10-methenyltetrahydrofolate synthetase from rabbit liver was determined by amino acid sequencing of the purified enzyme. The enzyme contains 201 amino acid residues with a predicted mass of 22,779 Da. The enzyme is located in the cytosolic fraction of liver homogenates. Carbodiimide-activated 5-formyltetrahydropteroylmonoglutamate and the pentaglutamate form of the substrate both irreversibly inactivate the enzyme by forming a covalent bond to Lys-18. Non-activated 5-formyltetrahydropteroylpentaglutamate protected against this inactivation. Substrate specificity studies showed that increasing the number of glutamate residues from zero to five on 5-formyltetrahydropteroate results in a 2 order of magnitude increase in the affinity of the substrate for the enzyme but only a 3-fold increase in the value of Vmax.
通过对纯化的兔肝5,10-亚甲基四氢叶酸合成酶进行氨基酸测序，确定了其一级序列。该酶含有201个氨基酸残基，预测分子量为22,779道尔顿。该酶位于肝匀浆的胞质部分。碳二亚胺活化的5-甲酰基四氢蝶酰单谷氨酸和底物的五谷氨酸形式均通过与赖氨酸-18形成共价键而使该酶不可逆地失活。未活化的5-甲酰基四氢蝶酰五谷氨酸可防止这种失活。底物特异性研究表明，5-甲酰基四氢蝶酸上的谷氨酸残基数量从零增加到五个，会使底物对该酶的亲和力增加2个数量级，但Vmax值仅增加3倍。
