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The article focuses on doctor Sandra L. Ballard's retirement from Appalachian State University after 24 years as the editor of Appalachian Journal. Topics include her significant contributions to promoting Appalachian writers and scholars, her influence on the academic field, and the lasting impact she had on her students, colleagues, and the wider community.

Glycine plays several roles in human metabolism, e.g. as a 1-carbon donor, in purine synthesis, and as a component of glutathione. Glycine is decarboxylated via the glycine cleavage system (GCS) that yields concurrent generation of a 1 -carbon unit as 5,10-methylenetetrahydrofolate (methyleneTHF). Serine hydroxymethyltransferase (SHMT) catalyzes the interconversion of glycine and serine, another 1-carbon donor. The quantitative role of glycine in human 1-carbon metabolism has received little attention. The aim of this protocol was to quantify whole body glycine flux, glycine to serine flux, and rate of glycine cleavage in humans. A primed, constant infusion with 9.26 [micro] mol.[kg.sup.-1] [h.sup.-1] [[1,2-.sup.13] [C.sub.2] ]glycine and 1.87 [micro] mol.[kg.sup.- 1] [h.sup.-1] [[2.sup.H.sub.3]]leucine was used to quantify the kinetic behavior of glycine in young, healthy volunteers (n = 5) in a fed state. The isotopic enrichment of infused tracers and metabolic products in plasma, as well as breath [13.sup.C][O.sub.2] enrichment, were determined for use in kinetic analysis. Serine synthesis by direct conversion from glycine via SHMT occurred at 193 [+ or -] 28 [micro] mol.[kg.sup.-1]. [h.sup.-1] (mean [+ or -] SEM), which comprised 41% of the 463 [+ or -] 55 [micro] mol.[kg.-1] [h.sup.-1] total glycine flux. Nearly one-half (46%) of the glycine-to-serine conversion occurred using GCS-derived methyleneTHF 1-carbon units. Based on breath [[13.sup.C][O.sub.2] measurement, glycine decarboxylation (190 [+ or -] 41 [micro] mol.[kg.sub.-1] [h.sup.-1]) accounted for 39 [+ or -] 6% of whole body glycine flux. This study is the first to our knowledge to quantify human glycine cleavage and glycine-to-serine SHMT kinetics. GCS is responsible for a substantial proportion of whole body glycine flux and constitutes a major route for the generation of 1-carbon units. J. Nutr. 137: 2647-2652, 2007.

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, 0.5, 0.1, or 0 mg of PN/kg diet, n = 5). This design allowed assessment of the effects of supplemental methionine (AIN-76A) vs. cysteine (AIN-93G) in common research diets over a range of vitamin B-6 levels. CBS activity, assayed in the presence or absence of added S-adenosylmethionine, was independent of diet type and PN level. CGL activity was independent of diet type but proportional to dietary PN. Rats fed deficient (0 and 0.1 mg PN/kg) diets exhibited only ~30% of the CGL activity of those fed the 2 mg PN/kg diets. Hepatic cystathionine increased from 20 to 30 nmol/g for the 1-2 mg PN/kg diets to ~85 nmol/g for the 0 mg PN/kg diet; however, cysteine was reduced only in B-6--deficient rats consuming the AIN-93G diet (means of 30-40 nmol/g for adequate to 11.6 nmol/g for 0 mg PN/kg AIN-76A diet). In spite of these effects, hepatic glutathione concentration increased in vitamin B-6 deficiency. These results suggest that vitamin B-6-dependent changes in transsulfuration do not limit hepatic glutathione production.

Hyperhomocysteinemia in humans is associated with genetic variants of several enzymes of folate and one-carbon metabolism and deficiencies of folate and vitamins [B.sub.12] and [B.sub.6]. In each case, hyperhomocysteinemia might be caused by diminished folate-dependent homocysteine remethylation, but this has not been confirmed in vivo. Because published stable isotopic tracer approaches cannot distinguish folate-dependent from folate-independent remethylation, we developed a dual-tracer procedure in which a [U-[sup.13][C.sub.5]]-methionine tracer is used in conjunction with a [3-[sup.13]C]serine tracer to simultaneously measure rates of total and folate-dependent homocysteine remethylation. In young female subjects, plasma [U-[sup.13][C.sub.4]]homocysteine enrichment, a surrogate measure of intracellular [U-[sup.13][C.sub.5]]methionine enrichment, reached ~90% of the plasma [U-[sup.13][C.sub.5]]methionine enrichment. Methionine-methyl and -carboxyl group fluxes were in the range of previous reports (~25 and ~17 [micro]mol*[kg.sup.-1]*[h.sup.-1], respectively). However, the rate of overall homocysteine remethylation (~8 [micro]mol*[kg.sup.-1]*[h.sup.-1]) was twice that of previous reports, which suggests a larger role for homocysteine remethylation in methionine metabolism than previously thought. By use of estimates of intracellular [3-[sup.13]C]serine enrichment based on a conservative correction of plasma [3-[sup.13]C]serine enrichment, serine was calculated to contribute ~100% of the methyl groups used for total body homocysteine remethylation under the conditions of this protocol. This contribution represented only a small fraction (~2.8%) of total serine flux. Our dual-tracer procedure is well suited to measure the effects of nutrient deficiencies, genetic polymorphisms, and other metabolic perturbations on homocysteine synthesis and total and folate-dependent homocysteine remethylation. methionine; methylation cycle; cystathionine

Cuskelly, Geraldine J., Peter W. Stacpoole, Jerry Williamson, Thomas G. Baumgartner, and Jesse F. Gregory III. Deficiencies of folate and vitamin [B.sub.6] exert distinct effects on homocysteine, serine, and methionine kinetics. Am J Physiol Endocrinol Metab 281: E1182-E1190, 2001.--Folate and vitamin [B.sub.6] act in generating methyl groups for homocysteine remethylation, but the kinetic effects of folate or vitamin [B.sub.6] deficiency are not known. We used an intravenous primed, constant infusion of stable isotope-labeled serine, methionine, and leucine to investigate one-carbon metabolism in healthy control (n = 5), folate-deficient (n = 4), and vitamin [B.sub.6]-deficient (n = 5) human subjects. The plasma homocysteine concentration in folate-deficient subjects [15.9 [+ or -] 2.1 (SD) [micro] molfl] was approximately two times that of control (7.4 [+ or -] 1.7 [micro] molfl) and vitamin B6-deficient (7.7 [+ or -] 2.1 [micro] mol/1) subjects. The rate of methionine synthesis by homocysteine remethylation was depressed (P = 0.027) in folate deficiency but not in vitamin B6 deficiency. For all subjects, the homocysteine remethylation rate was not significantly associated with plasma homocysteine concentration (r = -0.44, P = 0.12). The fractional synthesis rate of homocysteine from methionine was positively correlated with plasma homocysteine concentration (r = 0.60, P = 0.031), and a model incorporating both homocysteine re-methylation and synthesis rates closely predicted plasma homocysteine levels (r = 0.85, P = 0.0015). Rates of homocysteine remethylation and serine synthesis were inversely correlated (r = -0.89, P < 0.001). These studies demonstrate distinctly different metabolic consequences of vitamin [B.sub.6] and folate deficiencies. one-carbon metabolism; remethylation; stable isotopes; human; vitamin B6; folate Received 5 March 2001; accepted in final form 19 July 2001

In a 10-wk study with nonpregnant women (21-27 y, n = 5-6 per group), subjects were fed a diet containing [approximately]68 nmol/d (30 [[micro]gram]/d) folate from food that was supplemented with folic acid in apple juice to yield a constant intake of 454, 680 or 907 nmol/d (200, 300 or 400 [[micro]gram]/d) to evaluate folate status and long-term in vivo kinetics. Reported here is an additional phase of this protocol conducted to determine the relationship between short-term urinary excretion after a single isotopically labeled dose and various measures of folate nutritional status. It was hypothesized that urinary excretion from a single [glutamate-2H4]folic acid ([2H4]folic acid) dose would increase in proportion to folate nutritional status due to saturable cellular uptake and retention processes along with saturation of renal reabsorption. Each subject was given 1.13 [micro]mol (500 [[micro]gram]) of [2H4]folic acid orally on the morning of d 70 of the study, followed by a complete 24-h urine collection. Urine was analyzed to determine the isotopic enrichment of urinary folate by gas chromatography-mass spectrometry and the concentration of urinary folate by HPLC. Urinary excretion of [2H4]folate was greatest at the 907 nmol/d intake and was positively correlated with serum folate concentration but was not correlated with erythrocyte folate. Excretion of [2H4]folate tended to be greatest when plasma homocysteine concentrations were low ( KEY WORDS: * folate * urinary excretion * homocysteine * stable isotopes * humans

Vitamin B-6 deficiency causes mild elevation in plasma homocysteine, but the mechanism has not been clearly established. Serine is a substrate in one-carbon metabolism and in the transsulfuration pathway of homocysteine catabolism, and pyridoxal phosphate (PLP) plays a key role as coenzyme for serine hydroxymethyltransferase (SHMT) and enzymes of transsulfuration. In this study we used [[sup.2][H.sub.3]]serine as a primary tracer to examine the remethylation pathway in adequately nourished and vitamin B-6-deficient rats [7 and 0.1 mg pyridoxine (PN)/kg diet]. [[sup.2][H.sub.3]]Leucine and [1-[sup.13]C]methionine were also used to examine turnover of protein and methionine pools, respectively. All tracers were injected intraperitoneally as a bolus dose, and then rats were killed (n = 4/time point) after 30, 60 and 120 min. Rats fed the low-PN diet had significantly lower growth and plasma and liver PLP concentrations, reduced liver SHMT activity, greater plasma and liver total homocysteine concentration, and reduced liver S-adenosylmethionine concentration. Hepatic and whole body protein turnover were reduced in vitamin B-6-deficient rats as evidenced by greater isotopic enrichment of [[sup.2][H.sub.3]]leucine. Hepatic [[sup.2][H.sub.2]]methionine production from [[sup.2][H.sub.3]]serine via cytosolic SHMT and the remethylation pathway was reduced by 80.6% in vitamin B-6 deficiency. The deficiency did not significantly reduce hepatic cystathionine-[Beta]-synthase activity, and in vivo hepatic transsulfuration flux shown by production of [[sup.2][H.sub.3]]cysteine from the [[sup.2][H.sub.3]serine increased over twofold. In contrast, plasma appearance of [[sup.2][H.sub.3]]cysteine was decreased by 89% in vitamin B-6 deficiency. The rate of hepatic homocysteine production shown by the ratio of [1-[sup.13]C]homocysteine/[1-[sup.13]C]methionine areas under enrichment vs. time curves was not affected by vitamin B-6 deficiency. Overall, these results indicate that vitamin B-6 deficiency substantially affects one-carbon metabolism by impairing both methyl group production for homocysteine remethylation and flux through whole-body transsulfuration. J. Nutr. 130: 1115-1123, 2000. KEY WORDS: * one-carbon metabolism * homocysteine * transsulfuration * vitamin B-6 * rats

In a 10-wk study of folate metabolism in nonpregnant women (21-27 y, n =5-6 per group), subjects were fed a diet containing [approximately]68 nmol/d (30 [[micro]gram]/d) folate from food. The remainder of the ingested folate was provided as folic acid in apple juice (as nonlabeled during wk 1-2, as [2H2]folic acid during wk 3-10) to yield a constant intake of 454, 680 or 907 nmol/d (200, 300 or 400 [[micro]gram]/d). Isotopic enrichment of total urinary folate and the primary catabolite para-acetamidobenzoylglutamate (ApABG) was determined. Isotopic enrichment of ApABG served as an indicator of labeling of tissue folates. A kinetic model consisting of fast- and slow-turnover nonsaturable pools and a saturable slow-turnover pool, with provisions for urinary and fecal excretion, catabolism and enterohepatic circulation, yielded a close fit to the data. Mean residence times for total body folate were 212, 169 and 124 d for folate intakes of 454, 680, and 907 nmol/d, respectively. The model predicted that variation in folate intake over this range had little effect on the mass of the large saturable folate pool; however, the fast-turnover nonsaturable pools increased in proportion to folate intake, whereas the slow nonsaturable pool also tended to increase. This model will aid in evaluation of folate turnover and in predicting kinetic consequences of physiologic conditions associated with altered folate requirements. KEY WORDS: * folate * kinetics * modeling * requirements * stable isotopes * humans

Presents information on a study that determines the relationship between controlled folate status and the extent of urinary excretion of deuterium-labeled folate derived from a bolus dose of deuterated folic acid. Subjects and methods; Results and discussion.

Glycine is a precursor in the synthesis of DNA, protein, glutathione, and one-carbon units. Glycine decarboxylation through glycine cleavage system (GCS) and glycine-serine transformation by serine hydroxymethyltransferase (SHMT) require pyridoxal phosphate (PLP) as coenzyme. Primed, constant infusions of 9.26 µmol/(kg*h) [1,2-13C2]glycine and 1.87 µ*h) [5,5,5-²H3]leucine were used to quantify whole body glycine flux, flux of glycine decarboxylation, glycine to serine flux, and their dependence on vitamin B6 status in healthy volunteers (4 male, 1 female; aged 21-34y). Mean (± SEM) concentration of plasma PLP decreased from 59 ± 20 nmol/L to 23 ± 4 nmol/L during a 28-d vitamin B6-restricted diet. The rate of [13C2]serine synthesis derived from [13C2]glycine via SHMT was 183 ± 5 µmol/(kg*h) pre and 202 ± 18 µmol/(kg*h) post vitamin B6 restriction. The rate of [13C1]serine synthesis via GCS and SHMT was 80 ± 12 µmol/(kg*h) before and 78 ± 12 µmol/(kg*h) after the diet. No significant enrichment of methionine was detected at the glycine infusion rate used. Breath CO2 data show a glycine decarboxylation rate of 66.6 ± 8.3 µmol/(kg*h) and 59.7 ± 4.0 µmol/(kg*h), respectively, indicating that GCS accounted for 37 ± 4% and 32 ± 2% of whole body glycine flux, respectively, before and after vitamin B6 restriction. [ABSTRACT FROM AUTHOR]

Examines the effects of folate and vitamin B6 deficiency on homocysteine, serine and methionine kinetics. Analysis on one-carbon metabolism; Depression of methionine synthesis by homocysteine remethylation; Risk factors for plasma homocysteine elevation.