scholarly journals Amino acid transport systems of lysosomes: Possible substitute utility of a surviving transport system for one congenitally defective or absent

1988 ◽  
Vol 8 (2) ◽  
pp. 121-129 ◽  
Author(s):  
Halvor N. Christensen
Keyword(s):  
Plasma Membrane ◽  
Amino Acid ◽  
Transport System ◽  
Amino Acid Transport ◽  
Transport Systems ◽  
Acid Transport

Ways in which other transport systems may compensate for one that is genetically defective are considered. Comparisons of the transport systems of organelles (here the lysosome) with the transport system at the plasma membrane has significant implications for chemotherapy.

scholarly journals Discrimination of two amino acid transport activities in 4F2 heavy chain- expressing Xenopus laevis oocytes

1998 ◽  
Vol 333 (3) ◽  
pp. 549-554 ◽  
Author(s):  
Angelika BRÖER ◽  
Bernd HAMPRECHT ◽  
Stefan BRÖER
Keyword(s):  
Amino Acid ◽  
Transport System ◽  
Amino Acid Transport ◽  
Transport Systems ◽  
Xenopus Laevis Oocytes ◽  
Acid Transport ◽  
Transport Activity ◽  
Independent System ◽  
Leucine Transport ◽  
Dependent Transport

Expression of the type II membrane proteins of the rbAT/4F2hc family in Xenopus laevisoocytes results in the induction of amino acid transport activity. To elucidate the mechanism of action, amino acid transport was investigated in oocytes expressing the surface antigen 4F2hc. Leucine transport was mediated by a Na+-independent and a Na+-dependent transport mechanism. Both systems could be further discriminated by their stereochemical constraints. Isoleucine, with a branch at the β-position, shared only the Na+-independent transport system with leucine. Both transport systems were sensitive to inhibition by arginine, but only the Na+-independent system was sensitive to inhibition by 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid. When compared with known transport systems the two transport activities could be described as similar to, but not identical with, mammalian systems b0,+ and y+L. The Na+-independent b0,+-like transport system was found both in rbAT and 4F2hc expressing oocytes, indicating that both proteins act in a similar way.

Molecular Biology of Mammalian Plasma Membrane Amino Acid Transporters

1998 ◽  
Vol 78 (4) ◽  
pp. 969-1054 ◽  
Author(s):  
MANUEL PALACÍN ◽  
RAÚL ESTÉVEZ ◽  
JOAN BERTRAN ◽  
ANTONIO ZORZANO
Keyword(s):  
Plasma Membrane ◽  
Amino Acid ◽  
Molecular Biology ◽  
Structure Function ◽  
Amino Acid Transport ◽  
Transport Systems ◽  
Amino Acid Transporters ◽  
Acid Transport ◽  
Cationic Amino Acid ◽  
Function Relationship

Palacı́n, Manuel, Raúl Estévez, Joan Bertran, and Antonio Zorzano. Molecular Biology of Mammalian Plasma Membrane Amino Acid Transporters. Physiol. Rev. 78: 969–1054, 1998. — Molecular biology entered the field of mammalian amino acid transporters in 1990–1991 with the cloning of the first GABA and cationic amino acid transporters. Since then, cDNA have been isolated for more than 20 mammalian amino acid transporters. All of them belong to four protein families. Here we describe the tissue expression, transport characteristics, structure-function relationship, and the putative physiological roles of these transporters. Wherever possible, the ascription of these transporters to known amino acid transport systems is suggested. Significant contributions have been made to the molecular biology of amino acid transport in mammals in the last 3 years, such as the construction of knockouts for the CAT-1 cationic amino acid transporter and the EAAT2 and EAAT3 glutamate transporters, as well as a growing number of studies aimed to elucidate the structure-function relationship of the amino acid transporter. In addition, the first gene ( rBAT) responsible for an inherited disease of amino acid transport (cystinuria) has been identified. Identifying the molecular structure of amino acid transport systems of high physiological relevance (e.g., system A, L, N, and x−c) and of the genes responsible for other aminoacidurias as well as revealing the key molecular mechanisms of the amino acid transporters are the main challenges of the future in this field.

scholarly journals Characterization of uptake and compartmentalization of 3,5,3'-tri-iodothyronine in cultured neonatal rat cardiomyocytes

2001 ◽  
Vol 171 (1) ◽  
pp. 183-192 ◽  
Author(s):  
HH van der Putten ◽  
BJ Joosten ◽  
PH Klaren ◽  
ME Everts
Keyword(s):  
Plasma Membrane ◽  
Amino Acid ◽  
Transport System ◽  
Cellular Uptake ◽  
Amino Acid Transport ◽  
Neonatal Rat ◽  
Acid Transport ◽  
Amino Acid Transport System ◽  
Rat Cardiomyocytes ◽  
Neonatal Rat Cardiomyocytes

The uptake of tri-iodothyronine (T(3)) in cultured neonatal rat cardiomyocytes was investigated and compared with the uptake of reverse T(3 )(rT(3)) and thyroxine (T(4)). Cellular compartmentalization of T(3) was studied by distinguishing T(3) activity associated with the plasma membrane from that in the cytosol or incorporated in the cell nucleus. T(3) and T(4) uptake displayed similar temperature dependencies which, in magnitude, differed from that of rT(3) uptake. T(3) uptake was Na(+ )independent, and sensitive to oligomycin and monodansylcadaverine (42-49% and 25% inhibition of 15-min cellular uptake respectively). Furthermore, T(3) uptake could be inhibited by tryptophan (20%) and tyrosine (12%), while 2-aminobicyclo[2,2,1]heptane-carboxylic acid had no effect. Co-incubation with tryptophan and oligomycin resulted in an additive inhibition of T(3) uptake (77%). We therefore conclude that (i) T(3) uptake is energy dependent, (ii) receptor-mediated endocytosis may be involved and (iii) the aromatic amino acid transport system T may play a role, while system L is not involved in T(3) transport in cardiomyocytes. Co-incubation with unlabeled iodothyronines showed that 3,3'-di-iodothyronine and T(3) itself were the most effective inhibitors of T(3) uptake (30% and 36% inhibition of 15-min cellular uptake respectively). At 15-min incubation time, 38% of the total cell-associated T(3) was present in the cytosol and nucleus, and 62% remained associated to the plasma membrane. Unidirectional uptake rates did not saturate over a free T(3) concentration range up to 3.9 microM. We have concluded that T(3) uptake in neonatal rat cardiomyocytes occurs by an energy- and temperature-dependent mechanism that may include endocytosis and amino acid transport system T, and is not sensitive to the Na(+) gradient. Elucidation of the molecular basis for the T(3) transporter is the subject of current investigation.

Osmotic Regulation of ATA2 mRNA Expression and Amino Acid Transport System A Activity

2001 ◽  
Vol 283 (1) ◽  
pp. 174-178 ◽  
Author(s):  
Roberta R. Alfieri ◽  
Pier-Giorgio Petronini ◽  
Mara A. Bonelli ◽  
Alessandro E. Caccamo ◽  
Andrea Cavazzoni ◽  
...  
Keyword(s):  
Amino Acid ◽  
Mrna Expression ◽  
Transport System ◽  
Amino Acid Transport ◽  
Osmotic Regulation ◽  
Acid Transport ◽  
Amino Acid Transport System ◽  
System A

Amino Acid Transport in a Water-mould: The Possible Regulatory Roles of Calcium and N6-(Δ2-isopentenyl)adenine

1975 ◽  
Vol 53 (9) ◽  
pp. 975-988 ◽  
Author(s):  
Danny P. Singh ◽  
Hérb. B. LéJohn
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Amino Acid Transport ◽  
Osmotic Shock ◽  
Inhibitory Effect ◽  
Transport Systems ◽  
Acid Transport ◽  
Isopentenyl Adenine ◽  
Energy Dependent ◽  
Water Mould

Transport of amino acids in the water-mould Achlya is an energy-dependent process. Based on competition kinetics and studies involving the influence of pH and temperature on the initial transport rates, it was concluded that the 20 amino acids (L-isomers) commonly found in proteins were transported by more than one, possibly nine, uptake systems. This is similar to the pattern elucidated for some bacteria but unlike those uncovered for all fungi studied to date. The nine different transport systems elucidated are: (i) methionine, (ii) cysteine, (iii) proline, (iv) serine–threonine, (v) aspartic and glutamic acids, (vi) glutamine and asparagine, (vii) glycine and alanine, (viii) histidine, lysine, and arginine, and (ix) phenylalanine–tyrosine–tryptophan and leucine–isoleucine–valine as two overlapping groups. Transport of all of these amino acids was inhibited by azide, cyanide, and its derivatives and 2,4-dinitrophenol. These agents normally interfere with metabolism at the level of the electron transport chain and oxidative phosphorylation. Osmotic shock treatment of the cells released, into the shock fluid, a glycopeptide that binds calcium as well as tryptophan but no other amino acid. The shocked cells are incapable of concentrating amino acids, but remain viable and reacquire this capacity when the glycopeptide is resynthesized.Calcium played more than a secondary role in the transport of the amino acids. When bound to the membrane-localized glycopeptide, it permits concentrative transport to take place. However, excess calcium can inhibit transport which can be overcome by chelating with citrate. Calculations show that the concentration of free citrate is most important. At low citrate concentrations (less than 1 mM) in the absence of exogenously supplied calcium, enhancement of amino acid transport occurs. At high concentrations (greater than 5 mM), citrate inhibits but this effect can be reversed by titrating with calcium. Evidently, the glycopeptide acts as a calcium sink to regulate the concentration of calcium made available to the cell for its membrane activities.N6-(Δ2-isopentenyl) adenine (a plant growth 'hormone') and analogues mimic the inhibitory effect of citrate and bind to the glycopeptide as well. Replot data for citrate and N6-(Δ2-isopentyl) adenine inhibition indicate that both agents have no more than one binding constant. These results implicate calcium, glycopeptide, and energy-dependent transport of solutes in some, as yet undefinable, way.

Placental amino acid transport

1995 ◽  
Vol 268 (6) ◽  
pp. C1321-C1331 ◽  
Author(s):  
A. J. Moe
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Human Placenta ◽  
Amino Acid Transport ◽  
Single Layer ◽  
Maternal Blood ◽  
Transport Systems ◽  
Amino Acid Transporters ◽  
Acid Transport ◽  
Principal Mechanism

Normal fetal growth and development depend on a continuous supply of amino acids from the mother to the fetus. The placenta is responsible for the transfer of amino acids between the two circulations. The human placenta is hemomonochorial, meaning that the maternal and fetal circulations are separated by a single layer of polarized epithelium called the syncytiotrophoblast, which is in direct contact with maternal blood. Transport proteins located in the microvillous and basal membranes of the syncytiotrophoblast are the principal mechanism for transfer from maternal blood to fetal blood. Knowledge of the function and regulation of syncytiotrophoblast amino acid transporters is of great importance in understanding the mechanism of placental transport and potentially improving fetal and newborn outcomes. The development of methods for the isolation of microvillous and basal membrane vesicles from human placenta over the past two decades has contributed greatly to this understanding. Now a primary cultured trophoblast model is available to study amino acid transport and regulation as the cells differentiate. The types of amino acid transporters and their distribution between the syncytiotrophoblast microvillous and basal membranes are somewhat unique compared with other polarized epithelia. These differences may reflect the unusual circumstance of this epithelium that is exposed to blood on both sides. The current state of knowledge as to the types of transport systems present in syncytiotrophoblast, their regulation, and the effects of maternal consumption of drugs on transport are discussed.

Sign in / Sign up

Export Citation Format

Share Document