ROLE OF GAMMA-GLUTAMYL TRANSPEPTIDASE (GGT) IN AMINO ACID TRANSPORT

Gamma glutamyl transpeptidase (GGT), an amino acid transport enzyme, was investigated in normal and degenerated sciatic nerve of rat. The enzyme activity, which is considered to be a marker for cerebrovascular endothelium, was found to be absent in microvessels of normal and degenerated nerves. In the perineurium of normal nerve, GGT activity was faint, while in degenerated nerve, it increased. The most striking finding of this study was the observation of GGT activity at the paranode of each normal myelinated axon. It is interesting that after axotomy (8 weeks), no GGT activity was observed in the Schwann cells of degenerated nerve. Thus, Schwann cell plasmalemma contributed to GGT staining only when this cell was in contact with an axon mature enough to cause it to produce myelin. We conclude that, in peripheral nerve, transmembrane amino acid transport is apparently regional and associated with the paranodal region of myelinated nerve fibers.

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gamma-Glutamyl Transpeptidase in Rat Ascites Tumor Cell LY-5. Lack of Functional Correlation of Its Catalytic Activity with the Amino Acid Transport

European Journal of Biochemistry ◽

10.1111/j.1432-1033.1977.tb11774.x ◽

1977 ◽

Vol 78 (2) ◽

pp. 609-615 ◽

Cited By ~ 34

Author(s):

Masayasu INOUE ◽

Seikoh HORIUCHI ◽

Yoshimasa MORINO

Keyword(s):

Catalytic Activity ◽

Amino Acid ◽

Tumor Cell ◽

Amino Acid Transport ◽

Ascites Tumor ◽

Acid Transport ◽

Gamma Glutamyl Transpeptidase ◽

Gamma Glutamyl ◽

Functional Correlation ◽

Glutamyl Transpeptidase

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Role of the gamma-glutamyl cycle in the regulation of amino acid translocation

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1989.257.6.e916 ◽

1989 ◽

Vol 257 (6) ◽

pp. E916-E922 ◽

Cited By ~ 5

Author(s):

J. R. Vina ◽

M. Palacin ◽

I. R. Puertes ◽

R. Hernandez ◽

J. Vina

Keyword(s):

Amino Acids ◽

Mammary Gland ◽

Amino Acid ◽

Amino Acid Transport ◽

Acid Transport ◽

Pregnant Rats ◽

Gamma Glutamyl ◽

Extracellular Signals ◽

Previously Treated

Amino acid translocation was studied in the mammary gland of lactating rats and in the placenta of pregnant rats. The uptake of amino acids by the mammary gland is maximal on days 10-14 of lactation and is minimal on days 19-21. However, on day 19 maximal uptake can be restored by injection of 1) small amounts of gamma-glutamyl amino acids, 2) 5-oxoproline, and 3) an inhibitor of 5-oxoprolinase. A severe decrease in uptake of amino acids at the peak of lactation is provoked by anthglutin, an inhibitor of gamma-glutamyltranspeptidase (GGT). Simultaneous injection of 5-oxoproline blocks these effects of anthglutin. In pregnant rats, inhibition (79%) of placental GGT activity by acivicin results in a 50% decrease of placental L-[U-14C]-alanine transfer and 70-80% decrease in its incorporation into the placental and fetal proteins. Infusion of 5-oxoproline to mothers previously treated with acivicin restored the L-[U-14C]-alanine transfer. Acivicin or 5-oxoproline did not modify the transfer and metabolism of D-[U14C]glucose by the fetal placental unit. These results show that the gamma-glutamyl cycle should not be considered a mechanism for amino acid transport but rather a generator of extracellular signals, gamma-glutamyl amino acids, that are converted intracellularly to 5-oxoproline, which activates uptake and/or metabolism of amino acids.

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Pattern and rate of disappearance of gamma-glutamyl transpeptidase activity in fetal and neonatal rat liver.

Journal of Histochemistry & Cytochemistry ◽

10.1177/31.11.6194205 ◽

1983 ◽

Vol 31 (11) ◽

pp. 1312-1316 ◽

Cited By ~ 23

Author(s):

P M Iannaccone ◽

J Koizumi

Keyword(s):

Amino Acid ◽

Bile Duct ◽

Neonatal Rat ◽

Acid Transport ◽

Gamma Glutamyl Transpeptidase ◽

Gamma Glutamyl ◽

Duct Epithelium ◽

Neonatal Liver ◽

Bile Duct Epithelium ◽

Glutamyl Transpeptidase

Gamma-glutamyl transpeptidase (gamma-GTP), an amino acid transport enzyme, has been demonstrated in a number of fetal and adult tissues of rodent and man. While the re-expression of the enzyme has been described in epithelia following carcinogen treatment or aging, little is known of the mechanism of its disappearance in some neonatal tissues. A description is presented of the rate and pattern of loss of histologically demonstrable gamma-GTP activity from fetal and neonatal liver of the rat. The number of hepatocytes with histologically demonstrable gamma-GTP activity declines rapidly from the 18th day of gestation. By the 6th day postpartum the activity is demonstrable in clusters of hepatocytes. By the 7th day postpartum there are essentially no hepatocytes with demonstrable activity, although the enzyme remains expressed in bile duct epithelium.

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