Partial characterization of folate uptake in microvillous membrane vesicles isolated from human placenta

The purpose of the present study was to determine biochemical parameters of folate uptake, and the putative contribution of the membrane-anchored folate receptor in microvillous membrane vesicles obtained from the syncytiotrophoblast of human term placenta. Uptake of [3H]-pteroylglutamic acid (PGA) by microvillous membrane vesicles was pH dependent with a maximum at pH 6.0, and attained equilibrium at 60 min of incubation. Uptake was higher in the presence of an inward pH gradient (pHout = 6.0; pHin = 7.5) than in the absence of the gradient (pHout = pHin = 6.0). The effect of changes in medium osmolality showed that both binding to the vesicular membrane and internalization contributed to the measured [3H]-PGA uptake. Equilibrium uptake experiments using [3H]-PGA concentrations within the physiological range of folate in blood serum showed that saturation was achieved at 30 nM and revealed a single class of binding sites with a Kd of 1.8 nM for [3H]-PGA. Cleavage of the glycosyl-phosphatidylinositol moiety of the folate receptor, which anchors the receptor to the membrane, with phosphatidylinositolspecific phospholipase C resulted in a reduction of about 80 per cent in [3H]-PGA uptake. In conclusion, our results showed that the folate uptake in the maternally facing membrane of the human placenta presents a saturable component and is mediated by the folate receptor to ensure an adequate maternal-fetal folate transfer.

Iron uptake from lactoferrin by intestinal brush-border membrane vesicles of human neonates

It is uncertain to what extent the binding of human lactoferrin (LF) to its receptor in the intestinal brush-border membrane affects iron uptake in infants. The purpose of this study was to investigate iron uptake from human LF by brush-border membrane vesicles (BBMV) obtained from the small intestine of human neonates. LF was purified from pooled human colostrum. Uptake experiments were performed by incubation of 55Fe-citrate or 55Fe-LF with BBMV, followed by rapid filtration through microporous filters. 55Fe uptake from LF by BBMV was dependent on pH, with a maximum at 7.5, and increased with incubation time, reaching a maximum at 1 min. When 55Fe was bound to citrate, uptake was slower (maximum at 5 min) and not dependent on pH. In both experiments, the maximum uptake of iron bound to LF was about twice that of iron bound to citrate (230 pmol and 105 pmol/mg microvillus protein, respectively). Partial degradation of LF in two fragments resulted in the loss of its capacity to increase iron uptake by BBMV. From these preliminary results we conclude that LF may increase iron absorption during the neonatal period, contributing to the high bioavailability of this mineral in human milk.

Lactoferrin levels and unsaturated iron-binding capacity in colostrum of Brazilian women of two socioecomic levels

The objetive of this study was to compare lactoferrin (LF) levels and unsaturated iron-binding capacity (UIBC) of colostrum from Brazilian women aged 20-38 years of low (N = 28) and high (N = 15) socioeconomic level. Both groups received a similar amount of supplental iron (25-65 mg/day) during pregnancy. We also determined the relationship between LF levels and UIBC, and between these components and maternal iron status. Both groups (low and high socieconomic level) showed adequate and similar mean hematocrit (35.0 ñ 13% and 35.9 ñ 1.3%, respectively) and serum ferritin (64 ñ 12 µg/1 and 57 ñ 12 µg/1, respectively) levels. Furthermore, LF levels (5.7 ñ 0.9 mg/ml and 5.5 ñ 0.6 mg/ml) and UIBC (3.8 ñ 0.3 µg/ml and 3/1 ñ 0.3 µg/ml) were not significantly different in the two groups of women, nor were they related to maternal hematocrit or serum ferritin. UIBC was significantly (P = 0.009), although weakly positively correlated (r= 0.45) with LF levels, suggesting that other colostrum ligands may contribute substantially to the capacity of colostrum to bind exogenous iron

Estado Nutricional y composición de la leche materna en Hierro, Zinc, Folato y Vitamina B12 de madres de bajo nivel socioeconómico de Río de Janeiro / Nutritional status and iron, zinc, folate and vitamin B12 milk composition in mothers of low socioeconomic level in Río de Janeiro

El objetivo del estudio fue verificar si el uso durante el embarazo de suplemento de hierro, folato y vitamina B12 por mujeres brasileñas de bajo nivel socioeconómico es suficiente para lograr un estado nutricional satisfactorio en estos nutrientes durante la amamantación y una composición adecuada de la leche. Como complemento del estudio fue analizado el estado nutricional de las madres y la composición de la leche en relación al zinc. Considerando los valores promedio, el estado nutricional de las madres en relación a los nutrientes estudiados fue adecuado. Sin embargo algunas madres tuvieron índices menores que los normales para mujeres no embarazadas. Estos bajos índices especialmente 30 días después del parto, sugieren que estas madres presentan un estado nutricional inadecuado. La composición de la leche en relación a los nutrientes estudiados fue comparable a la de mujeres bien nutridas de países desarrollados. Las madres que recibieron suplemento de folato durante el embarazo tuvieron niveles más altos en el suero inmediatamente después del parto, que las que no recibieron suplemento. Sin embargo, la composición de la leche no fue afectada. Se concluye que el suplemento recibido fue insuficiente para cubrir las demandas de este período y mantener reservas adecuadas

Characterization of the vitamin B12 - binding protein isolated from sow's milk and its affinity for cyanocobalamin and other corrinoids

1. Unsaturated vitamin B12-binding protein was isolated from sow's milk whey by affinity chromatography on a vitamin B12-Sepharose colmn with a yield of 54% (3920-fold purification). The purified binding protein was homogeneous was homogeneous by the criteria of polyacrylamide gel electrophoresis and high speed sedimentation equilibrium. 2. The isolated vitamin B12-biding protein was a glycoprotein was a glycoprotein with 24% carbohydrates (fucose, galactose, mannose, galactosamine, glucosamine and sialic acid_ and high levels of aspartic and glutamic acids. The protein which has a molecular weight of 61800 determined by ultracentrifugation, consisted of a single polypepide chain, bound vitamin B12 on an equimolar vasis and had a partial specific volume of 0.697 ml/g (mechanical oscillaltor technique). 3. Its dissociation constant, Kd'for cyanocoballamin was 8.8 x 10-10M. The binding protein showed similar affinities for hidroxo-, and adenosylcobalamin when compared to cyanocobalamin relative affinity ratios, but lower affinities (31-49%) for cobinamide, Co-alfa [adenyl] cobamide and Co-alfa-[2-methyl-adenyl]cobamide. Therefore, the substitution of axial ligand to the cobalt atom in the corin ring of vitamin B12 had no effect on affinity, whereas the differences in the nucleotide part of the molecule caused a small decrease in energy of the interation. 4. The present results indicate close similarity of the vitamin B12-binding protein from sow's milk to vitamin B12-biding proteins from other