Mathis G A, Wyss P A, Schuetz E G, Hughey R P, Sirica A E
Department of Pathology, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298.
J Cell Physiol. 1991 Feb;146(2):234-41. doi: 10.1002/jcp.1041460207.
Freshly isolated hepatocytes from normal adult rat liver do not express measurable gamma-glutamyl transpeptidase (GGT) mRNA in contrast to the significant GGT mRNA levels expressed by normal adult rat kidney and hyperplastic bile ductular tissue from bile duct-ligated rats. However, the induction of GGT activity in rat hepatocytes by two-thirds hepatectomy was accompanied by the appearance of a high level of GGT mRNA. We are now able to demonstrate that normal adult rat hepatocytes express 5 protein bands which cross-react with 2 different anti-rat kidney GGT antisera. The apparent molecular weights were 26.9, 58.0, 63.9, 73.5, and 83.4 kDa, respectively. Expression of the 26.9- and 58.0-kDa proteins strikingly parallels the pattern of induction of GGT enzymatic activity. This suggests that these 2 proteins correspond to the active dimeric enzyme previously described in kidney and neoplastic hepatocellular tissue. In normal hepatocytes, the 73.5-kDa protein represents 50% of the total GGT-immunoreactive protein, in contrast to kidney, where this band contains less than 4% of the GGT protein. The kinetics of expression of the 73.5-kDa protein upon induction of GGT activity in hepatocytes, as well as in culture turnover studies, suggests that this protein is a precursor form of the active enzyme, such as the described 78/79-kDa single-chain glycoprotein propeptide of GGT. It appears that in normal hepatocytes, this precursor is not processed to the same extent as in kidney or in hyperplastic bile ductular tissue.
与正常成年大鼠肾脏以及胆管结扎大鼠的增生性胆管组织中显著表达的γ-谷氨酰转肽酶（GGT）mRNA水平相比，从正常成年大鼠肝脏中新鲜分离的肝细胞不表达可检测到的GGT mRNA。然而，三分之二肝切除诱导大鼠肝细胞中GGT活性时，伴随着高水平GGT mRNA的出现。我们现在能够证明，正常成年大鼠肝细胞表达5条与2种不同的抗大鼠肾脏GGT抗血清发生交叉反应的蛋白条带。其表观分子量分别为26.9、58.0、63.9、73.5和83.4 kDa。26.9 kDa和58.0 kDa蛋白的表达与GGT酶活性的诱导模式显著平行。这表明这两种蛋白对应于先前在肾脏和肿瘤性肝细胞组织中描述的活性二聚体酶。在正常肝细胞中，73.5 kDa蛋白占总GGT免疫反应性蛋白的50%，而在肾脏中，该条带所含GGT蛋白不到4%。肝细胞中GGT活性诱导时73.5 kDa蛋白的表达动力学以及培养物周转研究表明，该蛋白是活性酶的前体形式，如所描述的GGT 78/79 kDa单链糖蛋白前肽。似乎在正常肝细胞中，这种前体的加工程度与肾脏或增生性胆管组织中的不同。
