| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Biomedical Sciences Division, King's College, London, UK.
1. The roles of the gamma-glutamyl cycle and the anionic amino acid transport system xc- in mediating L-cystine uptake were investigated in cultured human pancreatic duct PaTu 8902 cells. This cell line exhibits morphological features of normal pancreatic duct cells and expresses gamma-glutamyl transpeptidase (gamma-GT, EC 2.3.2.2), an enzyme involved in the metabolism and regulation of intracellular glutathione (GSH). 2. Uptake of L-cystine (10 microM) was linear for up to 10 min, temperature dependent, Na+ independent, saturable (Michaelis-Menten constant (Km), 86 +/- 25 microM; maximal velocity (Vmax), 109 +/- 33 nmol (mg protein)-1 h-1) and reduced by 80-90% by a 50-fold excess concentration of L-glutamate and L-homocysteic acid, but not L-aspartate. These transport properties resemble those described for system xc-, which exchanges cystine for intracellular glutamate. 3. Acivicin, a known inhibitor of gamma-GT, decreased gamma-GT activity from 2.58 +/- 0.96 to 0.97 +/- 0.11 mU (mg protein)-1 and decreased the initial rates of L-cystine and L-glutamine uptake by 41-55%. Anthglutin (1-gamma-L-glutamyl-2-(2-carboxyphenylhyl)hydrazine), a structurally different inhibitor of gamma-GT, also caused a concentration-dependent (0.01-1 mM) decrease in gamma-GT activity and L-cystine uptake. 4. Neither acivicin nor anthglutin inhibited the uptake of L-glutamate, a poor substrate for gamma-GT. 5. In the presence of a 500-fold excess concentration of glutamate, which should abolish entry of cystine via system xc-, the remaining fraction of cystine transport was inhibited by 50% by acivicin, suggesting that transport is, in part, dependent on the activity of gamma-GT. 6. Cystine transport was also 60-80% inhibited by a series of gamma-glutamyl amino acids (5 mM) including gamma-glutamyl-glutamate, gamma-glutamyl-glutamine and gamma-glutamyl-glycine. alpha-Dipeptides inhibited cystine transport by only 6-22%. 7. These findings demonstrate that in human pancreatic duct PaTu 8902 cells, cystine uptake is mediated by system xc- (50-60%) and the gamma-glutamyl cycle. Our results provide the first evidence linking gamma-GT with cystine transport in human epithelial cells and are of relevance in view of the importance of cystine as a sulphur amino acid source for GSH synthesis in cells exposed to oxidative stress.
This article has been cited by other articles:
|
|
 |
|
  S. L. Johnston, K. E. Kitson, J. W. Tweedie, S. R. Davis, and J. Lee {gamma}-Glutamyl Transpeptidase Inhibition Suppresses Milk Protein Synthesis in Isolated Ovine Mammary Cells J Dairy Sci, February 1, 2004; 87(2): 321 - 329. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. E. Mann, D. L. Yudilevich, and L. Sobrevia Regulation of Amino Acid and Glucose Transporters in Endothelial and Smooth Muscle Cells Physiol Rev, January 1, 2003; 83(1): 183 - 252. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. Li, Z. M. Marshall, and A. R. Whorton Stimulation of cystine uptake by nitric oxide: regulation of endothelial cell glutathione levels Am J Physiol Cell Physiol, April 1, 1999; 276(4): C803 - C811. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. C. M. Siow, H. Sato, D. S. Leake, J. D. Pearson, S. Bannai, and G. E. Mann Vitamin C Protects Human Arterial Smooth Muscle Cells Against Atherogenic Lipoproteins : Effects of Antioxidant Vitamins C and E on Oxidized LDL–Induced Adaptive Increases in Cystine Transport and Glutathione Arterioscler. Thromb. Vasc. Biol., October 1, 1998; 18(10): 1662 - 1670. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 W.-J. Lee, RichardA. Hawkins, DarrylR. Peterson, and JuanR. Vina Role of Oxoproline in the Regulation of Neutral Amino Acid Transport across the Blood-Brain Barrier J. Biol. Chem., August 9, 1996; 271(32): 19129 - 19133. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
