Jones Dylan E, Ricker J David, Geary Laina M, Kosma Dylan K, Ryan Robert O
Department of Biochemistry and Molecular Biology University of Nevada Reno Reno Nevada USA.
Department of Chemistry University of Nevada Reno Reno Nevada USA.
JIMD Rep. 2020 Nov 11;58(1):61-69. doi: 10.1002/jmd2.12185. eCollection 2021 Mar.
3-Methylglutaconic (3MGC) aciduria is a common phenotypic feature of a growing number of inborn errors of metabolism. "Primary" 3MGC aciduria is caused by deficiencies in leucine pathway enzymes while "secondary" 3MGC aciduria results from inborn errors of metabolism that impact mitochondrial energy production. The metabolic precursor of 3MGC acid is -3MGC CoA, an intermediate in the leucine catabolism pathway. Gas chromatography-mass spectrometry (GC-MS) analysis of commercially available -3MGC acid yielded a mixture of and isomers while H-NMR spectroscopy of -3MGC acid at 25°C provided no evidence for the isomer. When -3MGC acid was incubated under conditions used for sample derivatization prior to GC-MS (but with no trimethylsilane added), H-NMR spectroscopy provided evidence of to isomerization. Incubation of -3MGC acid at 37°C resulted in time-dependent isomerization to -3MGC acid. -3MGC acid behaved in a similar manner except that, under identical incubation conditions, less isomerization occurred. In agreement with these experimental results, molecular modeling studies provided evidence that the energy minimized structure of -3MGC acid is 4 kJ/mol more stable than that for -3MGC acid. Once generated in vivo, -3MGC acid is proposed to isomerize via a mechanism involving π electron delocalization with formation of a resonance structure that permits bond rotation. The data presented are consistent with the occurrence of both diastereomers in urine samples of subjects with 3MGC aciduria.
3-甲基戊二酸（3MGC）尿症是越来越多先天性代谢缺陷中常见的表型特征。“原发性”3MGC尿症由亮氨酸途径酶缺乏引起，而“继发性”3MGC尿症则源于影响线粒体能量产生的先天性代谢缺陷。3MGC酸的代谢前体是β-3MGC辅酶A，它是亮氨酸分解代谢途径中的一种中间体。对市售的β-3MGC酸进行气相色谱-质谱（GC-MS）分析，得到了α和β异构体的混合物，而在25°C下对β-3MGC酸进行1H-NMR光谱分析，未发现α异构体的证据。当β-3MGC酸在用于GC-MS分析前样品衍生化的条件下孵育（但不添加三甲基硅烷）时，1H-NMR光谱提供了β向α异构化的证据。β-3MGC酸在37°C下孵育会导致随时间向α-3MGC酸异构化。α-3MGC酸表现出类似的方式，只是在相同的孵育条件下，异构化程度较小。与这些实验结果一致，分子建模研究提供了证据，表明β-3MGC酸的能量最小化结构比α-3MGC酸的结构稳定4 kJ/mol。一旦在体内生成，β-3MGC酸被认为会通过一种涉及π电子离域并形成允许键旋转的共振结构的机制进行异构化。所呈现的数据与3MGC尿症患者尿液样本中两种非对映异构体的存在情况一致。
