The biosynthetic origin of carbonyl oxygen of uroporphyrinogen III was investigated. A model experiment using methyl benzoate labeled with 13C and 18O revealed isotope shifts of 0.015 and 0.036 ppm, corresponding to alkoxy-18O- and carbonyl-18O-labeled carbonyl carbons, in the 13C-NMR spectrum. Doubly 18O-labeled methyl benzoate showed an isotope shift of 0.050 ppm, equal to the sum of the two singly 18O-labeled carbonyl carbons. Next, [1-13C, 1, 1, 4-18O3]5-aminolevulinic acid (ALA) was fed to Arthrobacter hyalinus, and the resulting porphyrin was esterified with trimethyloxonium tetrafluoroborate to afford 13C- and 18O-labeled uroporphyrin III octamethyl ester. The 13C-NMR signals exhibited carbonyl carbon 18O-isotope shifts of 0.013, 0.036 and 0.051 ppm, close to those obtained in the model experiment. Thus, the carbonyl oxygens of uroporphyrinogen III ang its oxidized product uroporpyrin III originated from ALA. This result shows that the loss of 18O at the acetate carbonyls of the A-ring in vitamin B12 does not occur before the formation of uroporphyrinogen III.
研究了尿
卟啉原 III 的羰基氧的
生物合成来源。使用 13C 和 18O 标记的
苯甲酸甲酯进行的模型实验显示,在 13C-NMR 光谱中,与烷氧基-18O-和羰基-18O-标记的羰基碳相对应的同位素位移分别为 0.015 和 0.036 ppm。双 18O 标记的
苯甲酸甲酯显示出 0.050 ppm 的同位素偏移,相当于两个单 18O 标记的羰基碳的总和。接着,将[1-13C, 1, 1, 4-18O3]
5-氨基乙酰丙酸(A
LA)注入透明节杆菌,得到的
卟啉与三甲基氧四
氟硼酸酯化,得到 13C 和 18O 标记的尿
卟啉 III 八甲酯。13C-NMR 信号显示羰基碳 18O 同位素偏移分别为 0.013、0.036 和 0.051 ppm,与模型实验中得到的信号接近。因此,uroporphyrinogen III ang 其氧化产物 uroporpyrin III 的羰基氧根来源于 A
LA。这一结果表明,
维生素 B12 中 A 环
乙酸酯羰基上 18O 的损失并不是在尿
卟啉原 III 形成之前发生的。