Amino Acid Transport Properties Research Articles

Detailed characterization of the UMAMIT proteins provides insight into their evolution, amino acid transport properties, and role in the plant.

Amino acid transporters play a critical role in distributing amino acids within the cell compartments and between plant organs. Despite this importance, relatively few amino acid transporter genes have been characterized and their role elucidated with certainty. Two main families of proteins encode amino acid transporters in plants: the amino acid-polyamine-organocation superfamily, containing mostly importers, and the UMAMIT (usually multiple acids move in and out transporter) family, apparently encoding exporters, totaling 63 and 44 genes in Arabidopsis, respectively. Knowledge of UMAMITs is scarce, based on six Arabidopsis genes and a handful of genes from other species. To gain insight into the role of the members of this family and provide data to be used for future characterization, we studied the evolution of the UMAMITs in plants, and determined the functional properties, the structure, and localization of the 47 Arabidopsis UMAMITs. Our analysis showed that the AtUMAMITs are essentially localized at the tonoplast or the plasma membrane, and that most of them are able to export amino acids from the cytosol, confirming a role in intra- and intercellular amino acid transport. As an example, this set of data was used to hypothesize the role of a few AtUMAMITs in the plant and the cell.

Developmental Effects of Intrauterine Growth Retardation on Cerebral Amino Acid Transport

Early restriction of nutrients during the perinatal period of life can modify the development of the mammalian fetus and have marked repercussions on the ontogeny of the CNS. The brain is vulnerable to undernutrition, with delayed morphologic and biochemical maturation leading to impaired functions. The aim of the present investigation was to assess whether modified brain neurotransmitter and amino acid concentrations found in an animal model of intrauterine growth retardation were related to modified blood-brain amino acid transport properties. Four amino acids were tested: alanine and taurine, plus two neurotransmitter precursors, tryptophan and tyrosine. Intrauterine growth retardation was induced by restriction of maternal-fetal blood flow from the 17th d of gestation. Blood-brain transport of these amino acids was measured by i.v. injection of radiolabeled amino acids in 7-d-old, 21-d-old, and 60-d-old intrauterine growth-retarded or control rats. No major statistical differences were revealed either for brain regional transport or between intrauterine growth-retarded animals and controls at any age studied. Transfer coefficients and influxes remained statistically similar for almost all brain regions in both groups. A significant decrease and different time course for amino acid transport with age related to the blood-brain barrier maturation are confirmed in this model. Our results are related to a major role of the blood-brain barrier as a part of mechanisms leading to "brain growth sparing."

Sugar and amino acid transport properties of the chicken ceca.

Chickens have two well-developed ceca, with an epithelium that is histologically and functionally heterogeneous. The proximal region, close to the ileorectal junction, has well-developed villi and microvilli and is able to transport sugars and amino acids against a concentration gradient, by mechanisms virtually identical to those described for the small intestine. The medial-distal region does not have true villi but has mounds and ridges, and it cannot transport either sugars or amino acids in the adult bird. In newborn chicks, the whole cecum can accumulate and transport sugars, but this property is soon restricted to the proximal region. The medial cecum, however, retains some transport capacity until the 8th week after the hatch. Ceca are thus well suited for sugar and amino acid absorption. Their contribution to the overall nutrient absorption is, however, limited, because the absorbing epithelium is exposed to the intestinal contents only during the filling and emptying of the cecal segments.

A rapid method for the reconstitution of Na+-dependent neutral amino acid transport from bovine renal brush-border membranes.

1. A simple and rapid method for the reconstitution of Na+-dependent neutral amino acid transport activity from bovine renal brush border membranes is described. 2. The neutral detergent decanoyl-N-methylglucamide ('MEGA-10') was employed to solubilize the membrane protein. This obviated the necessity for a prolonged dialysis step. 3. The properties of amino acid transport in these vesicles were similar to those observed in native membranes. 4. This should be a useful procedure in the eventual identification and isolation of amino acid transport proteins.

Neutral amino acid transport properties of cerebral endothelial cells in vitro.

An A and L system of neutral amino acid transport has been demonstrated previously in cerebral microvessels in vivo and in isolated microvessels in vitro. This report describes the neutral amino acid transport properties of cultured cerebral endothelial cells and investigates the influence of astroglia on the transport process. These studies confirm the presence of a sodium-dependent A-system and a sodium-independent L-system of neutral amino acid transport in cultured cerebral endothelial cells. The A-system transport is slower than L-system transport and each is variably inhibited by other amino acids. Transport is enhanced in log phase cells as compared to stationary phase contact-inhibited cells. Contact with glial cells or exposure to glial-conditioned media enhances neutral amino acid transport. These in vitro studies indicate that the A- and L-systems of neutral amino acid transport are in a dynamic state and are influenced by the phase of cell growth and contact with astroglia.

The effect of changes in osmolality on amino acid transport in the proximal convoluted tubule of the rat kidney.

In order to differentiate between the effect of increased amino acid (substrate) concentration and the accompanying rise in fluid osmolality on renal tubular amino acid transport properties, the transport of cycloleucine has been examined under conditions where the osmolality only was altered with raffinose. In stationary microperfusion experiments it has been demonstrated that an increase in osmolality to 400 mosmol/kg on both sides of the epithelium at once does not alter the active transporting capacity achieved. Although no experimental evidence is yet available, theoretical considerations suggest that neither component of this active transporting capacity, viz. active transepithelial transport rate or the permeability coefficient, would have changed.

Close linkage between the C blood group locus and the locus controlling amino acid transport in sheep erythrocytes.

Data from 838 Finnish Landrace or Finnish Landrace crossbred sheep showed a highly significant correlation between phenotypes of the C blood group system and erythrocyte amino acid transport variants. Erythrocytes with normal amino acid transport properties (GSH high, Ly- type) were Cb-positive or Cb-negative. Erythrocytes with the amino acid transport lesion (GSH low, Ly +) were never Cb-negative. Sheep erythrocytes homozygous for Cb showed stronger lysis reactions with anti-Cb than heterozygous cells. Ly + sheep were nearly always homozygous for Cb, whereas most Ly- sheep were heterozygous for Cb-negative. Inheritance studies provided strong evidence that this association is due to close genetic linkage.

Amino acid transport properties of erythrocytes from normal newborn lambs and lambs with an inherited defect in amino acid transport

An amino acid transport defect which occurs in the erythrocytes of adult sheep is also present in foetal erythrocytes from newborn lambs which have inherited the lesion. The transport defect in erythrocytes from adult sheep is associated with high intracellular levels of ornithine and lysine and a markedly diminished GSH concentration. Although the lesion in foetal cells also results in the accumulation of ornithine and lysine, the intracellular GSH concentration is only moderately diminished.