ABSTRACTy-Glutamyl transpeptidase (GGT) is an ectoenzyme that catalyzes the first step in the cleavage of glutathione (GSH) and plays an essential role in the metabolism of GSH and GSH conjugates of carcinogens, toxins, and eicosanoids. To learn more about the role of GGT in metabolism in vivo, we used embryonic stem cell technology to generate GGT-deficient (GGTml/GGTml) mice. GGTdeficient mice appear normal at birth but grow slowly and by 6 weeks are about half the weight of wild-type mice. They are sexually immature, develop cataracts, and have coats with a gray cast. Most die between 10 and 18 weeks. Plasma and urine GSH levels in the GGTml/GGTml mice are elevated 6-fold and 2500-fold, respectively, compared with wild-type mice. Tissue GSH levels are markedly reduced in eye, liver, and pancreas.Plasma cyst(e)ine levels in GGTm'/GGTml mice are reduced to '20% of wild-type mice. Oral administration of Nacetylcysteine to GGTml/GGTml mice results in normal growth rates and partially restores the normal agouti coat color. These findings demonstrate the importance of GGT and the y-glutamyl cycle in cysteine and GSH homeostasis.

LTC 4 -converting activity has a tissue distribution different from GGT with highest activity in spleen followed by small intestine, kidney, and pancreas and lower activity in liver and lung. The activity is membrane-bound and is inhibited by acivicin, a known inhibitor of GGT. The enzyme was partially purified from the small intestine of GGT-deficient mice by papain treatment and gel filtration chromatography. The partially purified fragment released by papain has an apparent molecular mass of 65-70 kDa and the same substrate specificity as the tissue homogenate. In addition to LTC 4 , S-decyl-GSH is also cleaved. GSH itself, oxidized GSH, and the synthetic substrates used to analyze GGT activity (␥-glutamyl-p-nitroanilide and ␥-glutamyl-4-methoxy-2-naphthylamide) are not substrates for this newly discovered enzyme. These data demonstrate that in addition to GGT at least one other enzyme cleaves LTC 4 in mice. To reflect this enzyme's preferred substrate, we suggest that it be named ␥-glutamyl leukotrienase.Peptidyl leukotrienes, cysteine-containing derivatives of arachidonic acid, are potent inducers of airway constriction, vasoconstriction, smooth muscle contraction, edema, and inflammation (1-4). LTC 4 1 is formed by conjugation of leukotriene A 4 with GSH (5) and is known to be cleaved by GGT, which removes the glutamyl moiety to form LTD 4 (6). LTC 4 conversion to LTD 4 has long been thought to be mediated solely by GGT (7,8). Recently, however, the existence of an activity termed GGT-rel has been identified in humans (9). GGT-rel shares an overall 40% amino acid sequence identity with human GGT and is capable of cleaving the ␥-glutamyl linkage of LTC 4 , but it is unable to hydrolyze synthetic substrates that are commonly used for assaying GGT. This activity has been reported to be absent in mice (9).The role of GGT in leukotriene metabolism is of interest because of the great potency of these compounds in responses to injury. However, the distribution of GGT activity and the sites of peptidyl leukotriene actions are not concordant. In the mouse, GGT tends to be expressed at very high levels in epithelia concerned with catabolism of GSH and reabsorption of its constituent amino acids (kidney and small intestine) and other ductular and secretory epithelia (pancreas and seminal vesicles) (7, 10 -12). It is characteristically low in organs in which leukotrienes may play a role in responses to injury (e.g. lung, heart, and lymphoid tissue (spleen)). In addition, the types of responses mediated by the peptidyl leukotrienes (vasoconstriction, bronchoconstriction, increases in vascular permeability, and mucus formation) do not occur in close proximity to sites where GGT is most abundant (13). Although there are reports of GGT activity in endothelium (14 -16), the discordance between peptidyl leukotriene targets and GGT activity raises the possibility that there are other LTC 4 -cleaving enzymes in the mouse.We have recently used homologous recombination to inactivate GGT in the mouse (12). Mice homozygous for th...

We used mice with a targeted disruption in g-glutamyl transpeptidase (GGT-deficient mice) to study the role of glutathione (GSH) in protection against oxygen-induced lung injury. These mice had reduced levels of lung GSH and restricted ability to synthesize GSH because of low levels of cysteine. When GGT-deficient mice were exposed to 80% oxygen, they developed diffuse pulmonary injury and died within eight days. Ten of 12 wild-type mice were alive after 18 days. Administration of N-acetylcysteine (NAC) to GGT-deficient mice corrected GSH values and prevented the development of severe pulmonary injury and death. Oxygen exposure induced an increase in lung GSH levels in both wild-type and GGT-deficient mice, but induced levels in the mutant mice were <50% of those in wild-type mice. Cysteine levels were approximately 50-fold lower than GSH levels the lungs of both wild-type and GGT-deficient mice. Levels of lung RNA coding for the heavy subunit of g-glutamyl cysteine synthetase rose three- to fourfold after oxygen exposure in both wild-type and GGT-deficient mice. In contrast, oxygen exposure failed to provoke increases in glutathione synthetase, glutathione peroxidase, glutaredoxin, or thioredoxin.

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Background and Purpose: Cerebral intraventricular infusion of acidic or basic fibroblast growth factor has been shown to attenuate ischemic damage to hippocampal CA1 neurons in the gerbil. The purpose of the present study was to determine if the basic fibroblast growth factor transgenic mouse has an enhanced