Evidence for two Na+-independent neutral amino acid transport systems in primary cultures of rat hepatocytes. Time-dependent changes in activity.

A membrane-bound γ-glutamyl transpeptidase is likely to be a key component of the 'amino acid site' of certain neutral amino acid transport systems. The hypothesis is in keeping with the Orlowski–Meister concept of a γ-glutamyl cycle for some forms of amino acid transport, and it is supported experimentally by a demonstration that the specificity of a γ-glutamyl transpeptidase (described herein) is virtually the same as the affinity of an amino acid site (described by Hajjar and Curran) for phenylalanine and 16 of its variously substituted analogues.Thus, both transpeptidase and transport site have a greater specificity for phenylalanine analogues having electron-withdrawing groups as substituents in the benzene ring than phenylalanine itself, and reduced specificity for analogues with electron-releasing substituents in the ring. The order of specificity according to ring substitution was −NO2 > −Cl > −F > −H > −CH3 > −OH > −NH2 for both systems. Again, the free α-amino group of phenylalanine plays a key role in the binding of the amino acid to the site, and it is also essential for the transpeptidase. Finally, the essential feature of the carboxyl group for binding of a neutral amino acid by the transport site is the −C = O group and this group is essential for maintaining the γ-glutamyl acceptor properties of an acceptor.

Download Full-text

Effects of different oxidizing agents on neutral amino acid transport systems in isolated bovine brain microvessels

Neurochemistry International ◽

10.1016/s0197-0186(01)00139-5 ◽

2002 ◽

Vol 41 (1) ◽

pp. 29-36 ◽

Cited By ~ 3

Author(s):

Patrizia Cardelli ◽

Sigfrido Scarpa ◽

Fabrizio Ceci ◽

Marco Lucarelli ◽

Fabio Tabacco ◽

...

Keyword(s):

Amino Acid ◽

Amino Acid Transport ◽

Bovine Brain ◽

Neutral Amino Acid ◽

Transport Systems ◽

Acid Transport ◽

Oxidizing Agents ◽

Brain Microvessels

Download Full-text

Expression of the surface antigen 4F2hc affects system-L-like neutral-amino-acid-transport activity in mammalian cells

Biochemical Journal ◽

10.1042/bj3240535 ◽

1997 ◽

Vol 324 (2) ◽

pp. 535-541 ◽

Cited By ~ 32

Author(s):

Stefan BRÖER ◽

Angelika BRÖER ◽

Bernd HAMPRECHT

Keyword(s):

Amino Acid ◽

Surface Antigen ◽

Amino Acid Transport ◽

Cho Cells ◽

Mammalian Cells ◽

Primary Cultures ◽

Transport Systems ◽

Acid Transport ◽

Transport Activity ◽

System L

Mammalian cells possess a variety of amino acid-transport systems with overlapping substrate specificity. System L is one of the major amino acid-transport systems of non-epithelial cells. By expression cloning we have recently demonstrated that the surface antigen 4F2hc (CD98) is a necessary component for expression of system-L-like amino acid-transport activity in C6-BU-1 rat glioma cells [Bröer, Bröer and Hamprecht (1995) Biochem. J. 312, 863–870]. 4F2hc mRNA was detected in CHO cells, COS cells, activated lymphocytes isolated from mouse spleen and primary cultures of astrocytes. In all these cell types, Na+-independent isoleucine transport was mediated by system L. No contribution of system y+L to isoleucine or arginine transport was detected in C6-BU-1 cells. In lymphocytes, both system-L-like amino acid-transport activity and 4F2hc mRNA levels increased after treatment with phorbol ester plus ionomycin. Antisense oligonucleotides caused modest inhibition of Na+-independent isoleucine transport in C6-BU-1 cells and primary cultures of astroglial cells, whereas arginine transport was unaffected. Overexpression of 4F2hc cDNA in CHO cells resulted in an increase in Na+-independent isoleucine transport.

Download Full-text