Production of 1-Carbon Units from Glycine Is Extensive in Healthy Men and Women  

Oleh:

Lamers, Yvonne ; Williamson, Jerry ; Theriaque, Douglas W. ; Shuster, Jonathan J.

Jenis: Article from Journal - ilmiah internasional
Dalam koleksi: JN: The Journal of Nutrition vol. 139 no. 04 (Apr. 2009), page 666-671.
Topik: Nutrient Physiology; Metabolism; and Nutrient-Nutrient Interactions

Ketersediaan

Perpustakaan FK Nomor Panggil: J42.K.2009.02 Non-tandon: 1 (dapat dipinjam: 0) Tandon: tidak ada

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Isi artikel

Glycine undergoes decarboxylation in the glycine cleavage system (GCS) to yield CO2, NH3, and a 1-carbon unit. CO2 also can be generated from the 2-carbon of glycine by 10-formyltetrahydrofolate-dehydrogenase and, after glycine-to-serine conversion by serine hydroxymethyltransferase, from the tricarboxylic acid cycle. To evaluate the relative fates of glycine carbons in CO2 generation in healthy volunteers (3 male, 3 female, aged 21–26 y), primed, constant infusions were conducted using 9.26 µmol•h–1•kg–1 of [1,2-13C]glycine and 1.87 µmol•h–1•kg–1 of [5,5,5-2H3]leucine, followed by an infusion protocol using [1-13C]glycine as the glycine tracer. The time period between the infusion protocols was >6 mo. In vivo rates of whole-body glycine and leucine flux were nearly identical in protocols with [1,2-13C]glycine and [5,5,5-2H3]leucine and with [1-13C]glycine and [5,5,5-2H3]leucine tracers, which showed high reproducibility between the tracer protocols. Using the [1-13C]glycine tracer, breath CO2 data showed a total rate of glycine decarboxylation of 96 ± 8 µmol•h–1•kg–1, which was 22 ± 3% of whole-body glycine flux. In contrast, infusion of [1,2-13C]glycine yielded a glycine-to-CO2 flux of 146 ± 37 µmol•h–1•kg–1 (P = 0.026). By difference, this implies a rate of CO2 formation from the glycine 2-carbon of 51 ± 40 µmol•h–1•kg–1, which accounts for 35% of the total CO2 generated in glycine catabolism. These findings also indicate that 65% of the CO2 generation from glycine occurs by decarboxylation, primarily from the GCS. Further, these results suggest that the GCS is responsible for the entry of 5,10-methylenetetrahydrofolate into 1-carbon metabolism at a very high rate ( 96 µmol•h–1•kg–1), which is 20 times the demand for methyl groups for homocysteine remethylation.

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