Vitamin B-6 deficiency suppresses the hepatic transsulfuration pathway but increases glutathione concentration in rats fed AIN-76A or AIN-93G diets.

The transsulfuration pathway, which aids in regulating homocysteine concentration and mediates cysteine synthesis, may be sensitive to vitamin B-6 status because cystathionine beta-synthase (CBS) and cystathionine gamma-lyase (CGL) require pyridoxal 5'-phosphate (PLP). To assess relations between vitamin B-6 and transsulfuration, we evaluated the effects of dietary pyridoxine (PN) on the hepatic concentration of relevant metabolites and in vitro activity of CBS and CGL. Growing rats were fed AIN-93G- or AIN-76A-based diets that ranged from adequate to deficient in vitamin B-6 (2, 1, 0.

Dietary vitamin B-6 restriction does not alter rates of homocysteine remethylation or synthesis in healthy young women and men.

Background: The effects of vitamin B-6 status on steady-state kinetics of homocysteine metabolism in humans are unclear.

Objective: The objective was to determine the effects of dietary vitamin B-6 restriction on the rates of homocysteine remethylation and synthesis in healthy humans.

Design: Primed, constant infusions of [(13)C(5)]methionine, [3-(13)C]serine, and [(2)H(3)]leucine were conducted in healthy female (n=5) and male (n=4) volunteers (20-30 y) before and after 4 wk of dietary vitamin B-6 restriction (<0.

Activities of hepatic cytosolic and mitochondrial forms of serine hydroxymethyltransferase and hepatic glycine concentration are affected by vitamin B-6 intake in rats.

Serine hydroxymethyltransferase (SHMT) is a pyridoxal phosphate (PLP)-dependent enzyme that exists as cytosolic and mitochondrial isozymes that catalyze the reversible interconversion of serine and tetrahydrofolate (THF) to glycine and 5,10-methyleneTHF. SHMT is a major source of one-carbon units for cellular metabolism, but its sensitivity to various degrees of altered vitamin B-6 nutritional status has not been determined. In this study, cytosolic and mitochondrial SHMT activities were measured in liver from rats fed dietary pyridoxine (PN) ranging from adequate to deficient levels (2, 1, 0.