Jones John G, Garcia Paula, Barosa Cristina, Delgado Teresa C, Caldeira M Madalena, Diogo Luisa
NMR Research Unit, Department of Biochemistry and Center for Neurosciences and Cell Biology, University of Coimbra, Portugal.
Magn Reson Med. 2008 Feb;59(2):423-9. doi: 10.1002/mrm.21451.
Exchange of hepatic glucose-6-phosphate (G6P) and glyceraldehyde-3-phosphate via transaldolase modifies hepatic G6P enrichment from glucose or gluconeogenic tracers. Transaldolase exchange was quantified in five healthy, fed subjects following an oral bolus of [1,2,3-(13)C(3)]glycerol (25-30 mg/kg) and paracetamol (10-12 mg/kg). (13)C Isotopomers of hepatic G6P were quantified by (13)C NMR spectroscopy of urinary glucuronide. [1,2,3-(13)C(3)]- and [4,5,6-(13)C(3)]glucuronide isotopomers, representing the conversion of [1,2,3-(13)C(3)]glycerol to G6P via dihydroxyacetone phosphate, were resolved from [1,2-(13)C(2)]- and [5,6-(13)C(2)]glucuronide (13)C-isotopomers, derived from metabolism of [1,2,3-(13)C(3)]glycerol via pyruvate and phosphoenolpyruvate. Enrichment of [1,2,3-(13)C(3)]glucuronide was significantly less than that of [4,5,6-(13)C(3)]glucuronide (1.30 +/- 0.57% versus 1.67 +/- 0.42%, P < 0.05). Also, [1,2-(13)C(2)]glucuronide enrichment was significantly less than that of [5,6-(13)C(2)]glucuronide (0.28 +/- 0.08% versus 0.36 +/- 0.03%, P < 0.05). Transaldolase and triose phosphate isomerase exchange activities were estimated by applying the (13)C-isotopomer data to a model of hepatic sugar phosphate metabolism. Triose phosphate isomerase exchange was approximately 99% complete and did not contribute significantly to the unequal (13)C-isotopomer distributions of the glucuronide triose halves. Instead, this was attributable to 25 +/- 23% of hepatic G6P flux undergoing transaldolase exchange. This results in substantial overestimates of indirect pathway contributions to hepatic glycogen synthesis with tracers such as [5-(3)H]glucose and (2)H(2)O.
通过转醛醇酶进行的肝葡萄糖-6-磷酸（G6P）和磷酸二羟丙酮之间的交换改变了来自葡萄糖或糖异生示踪剂的肝G6P富集情况。在五名健康、进食后的受试者口服给予[1,2,3-(13)C(3)]甘油（25 - 30 mg/kg）和对乙酰氨基酚（10 - 12 mg/kg）后，对转醛醇酶交换进行了定量分析。通过尿葡萄糖醛酸的(13)C核磁共振波谱对肝G6P的(13)C同位素异构体进行定量。代表[1,2,3-(13)C(3)]甘油通过磷酸二羟丙酮转化为G6P的[1,2,3-(13)C(3)] - 和[4,5,6-(13)C(3)]葡萄糖醛酸同位素异构体，与源自[1,2,3-(13)C(3)]甘油经丙酮酸和磷酸烯醇丙酮酸代谢的[1,2-(13)C(2)] - 和[5,6-(13)C(2)]葡萄糖醛酸(13)C - 同位素异构体得以区分。[1,2,3-(13)C(3)]葡萄糖醛酸的富集显著低于[4,5,6-(13)C(3)]葡萄糖醛酸（1.30±0.57%对1.67±0.42%，P < 0.05）。此外，[1,2-(13)C(2)]葡萄糖醛酸的富集显著低于[5,6-(13)C(2)]葡萄糖醛酸（0.28±0.08%对0.36±0.03%，P < 0.05）。通过将(13)C - 同位素异构体数据应用于肝磷酸糖代谢模型来估计转醛醇酶和磷酸丙糖异构酶的交换活性。磷酸丙糖异构酶交换约99%完成，对葡萄糖醛酸丙糖两半不相等的(13)C - 同位素异构体分布贡献不显著。相反，这归因于25±23%的肝G6P通量进行了转醛醇酶交换。这导致使用诸如[5-(3)H]葡萄糖和(2)H(2)O等示踪剂时，对肝糖原合成间接途径贡献的大幅高估。
