Differences in Affinity and Energetics of the Active Transport Systems for Amino Acids in Chang Liver Cells

1979 ◽  
Keyword(s):  
Amino Acids ◽  
Active Transport ◽  
Liver Cells ◽  
Transport Systems ◽  
Chang Liver

scholarly journals Characteristics of the transport of alanine, serine and glutamine across the plasma membrane of isolated rat liver cells

1978 ◽  
Vol 176 (3) ◽  
pp. 827-836 ◽  
Author(s):  
S K Joseph ◽  
N M Bradford ◽  
J D McGivan
Keyword(s):  
Amino Acids ◽  
Plasma Membrane ◽  
Isolated Hepatocytes ◽  
Liver Cells ◽  
Transport Systems ◽  
Cell Protein ◽  
Alanine Transport ◽  
Cell Plasma ◽  
Intracellular Content ◽  
Rat Liver Cells

1. Alanine, glutamine and serine were actively accumulated in liver cells isolated from starved rats. 2. This accumulation was inhibited when either Na+ or HCO3- ions were omitted from the incubation medium. In general the degree of dependence on Na+ was quantitatively similar to that on HCO3-. 3. The apparent Km values for the transport of all three amino acids were in the range 3–5mM with Vmax. values in the range 15–25nmol/min per mg of cell protein at 37 degrees C. 4. Alanine and serine transport were mutually competitive; glutamine inhibited the transport of alanine and serine non-competitively. 5. The initial rate of transport of these amino acids was inhibited when the intracellular content of ATP was decreased. 6. Ouabain inhibited the rate of alanine transport without inhibiting the rate of alanine metabolism. 7. It is concluded that a minimum of three transport systems must be postulated to exist in the liver cell plasma membrane to account for the transport of alanine, serine and glutamine. The rate of transport of these amino acids in isolated hepatocytes is unlikely to limit the rate at which they are metabolized.

Tertiary active transport of amino acids reconstituted by coexpression of System A and L transporters in Xenopus oocytes

2009 ◽  
Vol 297 (3) ◽  
pp. E822-E829 ◽  
Author(s):  
Fiona E. Baird ◽  
Kevin J. Bett ◽  
Catherine MacLean ◽  
Andrew R. Tee ◽  
Harinder S. Hundal ◽  
...  
Keyword(s):  
Amino Acids ◽  
Active Transport ◽  
Xenopus Oocytes ◽  
Plasma Concentrations ◽  
Transport Systems ◽  
Functional Coupling ◽  
Specific System ◽  
Tor Pathway ◽  
System A ◽  
System L

The System L transporter facilitates cellular import of large neutral amino acids (AAs) such as Leu, a potent activator of the intracellular target of rapamycin (TOR) pathway, which signals for cell growth. System L is an AA exchanger, proposed to accumulate certain AAs by coupling to dissipation of concentration gradient(s) of exchange substrates generated by secondary active AA transporters such as System A (SNAT2). We addressed the hypothesis that this type of coupling (termed tertiary active transport) acts as an indirect mechanism to extend the range of AA stimulating TOR to those transported by both Systems A and L (e.g., Gln) through downstream enhancement of Leu accumulation. System A overexpression enabled Xenopus oocytes to accumulate substrate AAs (notably Ser, Gln, Ala, Pro, Met; totaling 2.6 nmol/oocyte) from medium containing a physiological AA mixture at plasma concentrations. Net accumulation of System L (4F2hc-xLAT1) substrates from this medium by System L-overexpressing oocytes was increased by 90% (from 0.7 to 1.35 nmol/oocyte; mainly Leu, Ile) when Systems A and L were coexpressed, coincident with a decline in accumulation of specific System A substrates (Gln, Ser, Met), as expected if the latter were also System L substrates and functional coupling of the transport Systems occurred. AA flux coupling was confirmed as trans-stimulation of Leu influx in System L-expressing oocytes by Gln injection (0.5 nmol/oocyte). The observed changes in Leu accumulation are sufficient to activate the TOR pathway in oocytes, although intracellular AA metabolism limits the potential for AA accumulation by tertiary active transport in this system.

scholarly journals Transport of the aromatic amino acids into isolated rat liver cells. Properties of uptake by two distinct systems

1986 ◽  
Vol 233 (2) ◽  
pp. 499-506 ◽  
Author(s):  
M Salter ◽  
R G Knowles ◽  
C I Pogson
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Rat Liver ◽  
Transport System ◽  
Aromatic Amino Acids ◽  
Liver Cells ◽  
Transport Systems ◽  
Isolated Rat Liver ◽  
Rat Liver Cells ◽  
Isolated Rat

The transport of the aromatic amino acids into isolated rat liver cells was studied. There was a rapid and substantial binding of the aromatic amino acids, L-alanine and L-leucine to the plasma membrane. This has important consequences for the determination of rates of transport and intracellular concentrations of the amino acids. Inhibition studies with a variety of substrates of various transport systems gave results consistent with aromatic amino acid transport being catalysed by two systems: a 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid (BCH)-insensitive aromatic D- and L-amino acid-specific system, and the L-type system (BCH-sensitive). The BCH-insensitive component of transport was Na+-independent and facilitated non-concentrative transport of the aromatic amino acids; it was unaffected by culture of liver cells for 24 h, by 48 h starvation, dexamethasone phosphate or glucagon. Kinetic properties of the BCH-inhibitable component were similar to those previously reported for the L2-system in liver cells. The BCH-insensitive component was a comparatively low-Km low-Vmax. transport system that we suggest is similar to the T-transport system previously seen only in human red blood cells. The results are discussed with reference to the importance of the T- and L-systems in the control of aromatic L-amino acid degradation in the liver.

Some Observations On Platelet Amino Acid Transport Systems

1981 ◽  
Author(s):  
U T Yardimci ◽  
A Özbilen ◽  
O N Ulutin
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Active Transport ◽  
Amino Acid Transport ◽  
Acid Group ◽  
Transport Systems ◽  
Acid Transport ◽  
Amino Acid Group ◽  
Active Transport System ◽  
Group Transport

We have studied the transport systems for amino acids in platelets. Na+/K+ dependent active transport systems were found to be responsible for the transport of amino acids through the platelet membrane (Km’s being at uM ranges). We have also isolated the binding proteins for amino acids from platelet membranes as the carriers involved in these active transport systems by cold osmotic shock procedure. Each amino acid besides being transported by a specific active transport system may be subject to transport by group amino acid transport systems.Group amino acid transport systems are classified by countertransport experiments as follows: Neutral amino acid group transport systems: IA: glycine, alanine, serine, threonine IB: valine, leucine, isoleucine, serine,threonine IC: cysteine, methionine, proline Basic amino acid group transport systems: lie: lysine IIB: histidine, arginine Acidic amino acid group transport systems: III A: Aspartic acid, glutamic acid Aromatic amino acid group transport systems: IVC: Phenylalanine,tyrosine, histidine, proline.

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