Habib G M, Barrios R, Shi Z Z, Lieberman M W
Department of Pathology, Baylor College of Medicine, Houston, Texas 77030, USA.
J Biol Chem. 1996 Jul 5;271(27):16273-80. doi: 10.1074/jbc.271.27.16273.
Membrane-bound dipeptidase (MBD) participates in the degradation of glutathione by cleaving the cysteinyl-glycine bond of cystinyl bisglycine (oxidized cysteinyl-glycine) following removal of a gamma-glutamyl group by gamma-glutamyl transpeptidase (GGT). In the mouse, MBD RNA is most abundant in small intestine, kidney, and lung and is represented by four distinct RNA species. These are generated by transcription from two promoters located 6 kilobases apart in the 5' flanking region of the gene and by the use of two different poly(A) addition sites. Promoter I is used primarily in small intestine and kidney, whereas promoter II is most active in lung and kidney. We found a discordance in the expected co-expression of MBD and GGT; as expected, MBD and GGT are both expressed at high levels in the kidney and small intestine. However, in the lung, MBD is expressed at high levels, whereas GGT is almost undetectable. The reverse is true in the seminal vesicles and fetal liver. Thus, although both enzymes may function in concert to metabolize glutathione in kidney and small intestine, in other tissues they appear to act independently, suggesting that they have independent roles in other biological processes.
膜结合二肽酶（MBD）通过γ-谷氨酰转肽酶（GGT）去除γ-谷氨酰基后，裂解胱氨酰双甘氨酸（氧化型半胱氨酰甘氨酸）的半胱氨酰-甘氨酸键，参与谷胱甘肽的降解。在小鼠中，MBD RNA在小肠、肾脏和肺中最为丰富，由四种不同的RNA种类代表。这些是由位于基因5'侧翼区域相距6千碱基的两个启动子转录以及使用两个不同的聚腺苷酸化位点产生的。启动子I主要在小肠和肾脏中使用，而启动子II在肺和肾脏中最活跃。我们发现MBD和GGT预期的共表达存在不一致；正如预期的那样，MBD和GGT在肾脏和小肠中均高表达。然而，在肺中，MBD高表达，而GGT几乎检测不到。在精囊和胎儿肝脏中情况相反。因此，尽管这两种酶可能在肾脏和小肠中协同作用以代谢谷胱甘肽，但在其他组织中它们似乎独立发挥作用，这表明它们在其他生物学过程中具有独立的作用。
