Intestinal Alkaline Phosphatase Isoforms in Rabbit Tissues Differ in Glycosylation Patterns

Objectives: In patients with advanced liver cirrhosis or chronic nephritis, an intestinal alkaline phosphatase (IAP)-like enzyme is ectopically expressed in the liver or kidney. In this study, we used rabbit organs as a human pathological model, because the rabbit liver or kidney expresses an IAP-like enzyme as the predominant isozyme, unlike humans. Methods: IAP and the IAP-like enzyme were purified from rabbit intestine and kidney, respectively, by immunoaffinity chromatography using a monoclonal antihuman IAP antibody. Some properties of the IAP and IAP-like enzyme expressed in rabbit organs are compared. Results: Some of their catalytic and physicochemical properties differed. In particular, the net charge, molecular mass, and hydrophobicity of IAP from rabbit intestine was slightly different from the IAP-like enzyme from rabbit kidney. There was a difference in the sugar chain structure between the two enzymes according to the results of lectin affinity chromatography, and part of the peptide maps differed slightly. However, there was no difference in the peptide maps after treatment with endo-N-acetylglucosaminidase F. Conclusions: The primary structures of IAP and the IAP-like enzyme are basically similar, except for the glycosylation process of the respective AP isozymes.