Moderate Dietary Vitamin B-6 Restriction Raises Plasma Glycine and Cystathionine Concentrations While Minimally Affecting the Rates of Glycine Turnover and Glycine Cleavage in Healthy Men and Women  

Oleh:

Lamers, Yvonne ; Williamson, Jerry ; Ralat, Maria ; Quinlivan, Eoin P. ; Gilbert, Lesa R.

Jenis: Article from Journal - ilmiah internasional
Dalam koleksi: JN: The Journal of Nutrition vol. 139 no. 03 (Mar. 2009), page 452.

Ketersediaan

Perpustakaan FK Nomor Panggil: J42.K.2009.01 Non-tandon: 1 (dapat dipinjam: 0) Tandon: tidak ada

Lihat Detail Induk

Isi artikel

Glycine is a precursor of purines, protein, glutathione, and 1-carbon units as 5,10-methylenetetrahydrofolate. Glycine decarboxylation through the glycine cleavage system (GCS) and glycine-serine transformation by serine hydroxymethyltransferase (SHMT) require pyridoxal 5'-phosphate (PLP; active form of vitamin B-6) as a coenzyme. The intake of vitamin B-6 is frequently low in humans. Therefore, we determined the effects of vitamin B-6 restriction on whole-body glycine flux, the rate of glycine decarboxylation, glycine-to-serine conversion, use of glycine carbons in nucleoside synthesis, and other aspects of 1-carbon metabolism. We used a primed, constant infusion of [1,2-13C2]glycine and [5,5,5-2H3]leucine to quantify in vivo kinetics in healthy adults (7 males, 6 females; 20–39 y) of normal vitamin B-6 status or marginal vitamin B-6 deficiency. Vitamin B-6 restriction lowered the plasma PLP concentration from 55 ± 4 nmol/L (mean ± SEM) to 23 ± 1 nmol/L (P < 0.0001), which is consistent with marginal deficiency, whereas the plasma glycine concentration increased (P < 0.01). SHMT-mediated conversion of glycine to serine increased from 182 ± 7 to 205 ± 9 µmol·kg–1·h–1 (P < 0.05), but serine production using a GCS-derived 1-carbon unit (93 ± 9 vs. 91 ± 6 µmol·kg–1·h–1) and glycine cleavage (163 ± 11 vs. 151 ± 8 µmol·kg–1·h–1) were not changed by vitamin B-6 restriction. The GCS produced 1-carbon units at a rate (140–170 µmol·kg–1·h–1) that greatly exceeds the demand for remethylation and transmethylation processes (4–7 µmol·kg–1·h–1). We conclude that the in vivo GCS and SHMT reactions are quite resilient to the effects of marginal vitamin B-6 deficiency, presumably through a compensatory effect of increasing substrate concentration.

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