Leukotriene D ₄ and cystinyl-bis-glycine metabolism in membrane-bound dipeptidase-deficient mice

Abstract

We have developed mice deficient in membrane-bound dipeptidase (MBD, EC 3.4.13.19), the enzyme believed to be responsible for the conversion of leukotriene D 4 (LTD 4 ) to leukotriene E 4 (LTE 4 ). The MBD mutation generated by us was demonstrated to be a null mutation by Northern blot analysis and the absence of ␤-lactamase activity in lung, kidney, small intestine, and heart. MBD gene deletion had no effect on viability or fertility. The mutant mice retain partial ability to convert LTD 4 to LTE 4 , ranging from 80-90% of the wild-type values in small intestine and liver to 16% in kidney and 40% in lung, heart, and pancreas. MBD is also believed to function consecutively after ␥-glutamyl transpeptidase to cleave cystinyl-bis-glycine (cys-bis-gly) generated from glutathione cleavage. Our data indicate that kidney homogenates from MBD-deficient mice retain ϳ40% of their ability to cleave cys-bis-gly, consistent with only modest elevations (3-5-fold) of cys-bis-gly in urine from MBDdeficient mice. These observations demonstrate that the conversion of LTD 4 to LTE 4 and the degradation of cys-bis-gly are catalyzed by at least two alternative pathways (one of which is MBD) that complement each other to varying extents in different tissues.

Disruption of γ-Glutamyl Leukotrienase Results in Disruption of Leukotriene D4 Synthesis In Vivo and Attenuation of the Acute Inflammatory Response

“…We employed our standard HPLC-based method to analyze endogenously formed LT metabolites in peritoneal lavage fluid (4,15). One would expect in zymosan A-exposed wild-type mice that newly synthesized LTC 4 would be rapidly converted first to LTD 4 by GGT and/or GGL and then to LTE 4 by membrane-bound dipeptidase(s) (14,15). As shown in Fig.…”

“…To investigate the in vivo role of each enzyme in LTC 4 metabolism during the inflammatory response, we induced peritonitis by injection of zymosan A into the peritoneal cavity of wild-type and mutant mice (10,30). We employed our standard HPLC-based method to analyze endogenously formed LT metabolites in peritoneal lavage fluid (4,15). One would expect in zymosan A-exposed wild-type mice that newly synthesized LTC 4 would be rapidly converted first to LTD 4 by GGT and/or GGL and then to LTE 4 by membrane-bound dipeptidase(s) (14,15).…”

γ-Glutamyl Leukotrienase, a γ-Glutamyl Transpeptidase Gene Family Member, Is Expressed Primarily in Spleen

“…In other experiments, we have produced membrane-bound dipeptidase-deficient mice and found that tissues from these mice are capable of metabolizing LTD 4 to LTE 4 , the Cys derivative (27). Thus, like the cleavage of GSH conjugates, more than one enzyme is capable of catalyzing the second step of this pathway.…”

Purified γ-Glutamyl Transpeptidases from Tomato Exhibit High Affinity for Glutathione and GlutathioneS-Conjugates

“…The ␥-glutamyl peptides resulting from the transpeptidation reaction may enter the "␥-glutamyl cycle," where they are also hydrolyzed and the amino acids are salvaged (Meister, 1988(Meister, , 1989. Cys-Gly dipeptidases complete the hydrolysis of GSH (Habib et al, 1998). Second, ␥ GTases are part of the pathway for detoxification and elimination of many xenobiotics and pharmaceuticals (Meister, 1988;Ishikawa, 1992).…”