Similarity of the sugar moiety of human alkaline phosphatases between the kidney cortex and duodenum, or medulla and ileum

Alkaline phosphatases reduce toxicity of lipopolysaccharides in vivo and in vitro through dephosphorylation

Intestinal alkaline phosphatase (AP), as a host defense factor, was first investigated in vivo using rats orally exposed to lipopolysaccharide (LPS). After the oral administration of LPS to rats, serum LPS content was increased within 2 hr and then decreased to 6 hr. In contrast, when L-phenylalanine (L-Phe), an inhibitor of intestinal-type AP isozymes, was simultaneously administered with LPS, serum LPS content significantly increased from 1 hr and the area under the concentration-time curve of serum LPS was augmented approximately 2-fold, suggesting that APs in the gastrointestinal tract reduced serum LPS content. In addition, LPS toxicity diminished by a treatment in vitro with intestinal APs, were recovered by the treatment in the co-presence of L-Phe. In the experiment using human aortic endothelial cells (HAECs), we observed that the cell viability decreased in a dose-dependent manner of LPS-exposure, and the LPS dose, exhibiting 50% viability of the cells, was 0.05 microg/ml. When the cells were exposed to LPS pretreated with 50 nIU/ml of intestinal AP at pH 10.0 and 8.0, the 50% viability was at 2.0 microg/ml of LPS. These results strongly suggest that the APs reduced the toxicity of LPS, as a host defense factor against LPS.

Detergent-mediated reconstitution of a glycosyl-phosphatidylinositol-protein into liposomes

A three-step detergent-mediated reconstitution has been applied to the incorporation of a glycosyl-phosphatidylinositol-protein into liposomes. The protein studied was alkaline phosphatase from bovine intestine. Liposomes prepared by dialysis were treated with various amounts of two detergents, either n-octyl beta-D-glucoside or Triton X-100. At different steps of the solubilization process, protein was added and the detergent was removed by hydrophobic resins. The most efficient reconstitutions were obtained with an octyl glucoside concentration corresponding to the onset of liposome solubilization and with a Triton X-100 concentration leading to partial solubilization of the liposomes. The involvement of the glycosyl-phosphatidylinositol anchor in alkaline phosphatase reconstitution was demonstrated by the inability of phosphoinositol-specific phospholipase-C-hydrolysed alkaline phosphatase to incorporate into liposomes. Between 70-85% of the protein associated with liposomes were anchored in the outer leaflet of the bilayer, oriented towards the outside of the liposome. The remainder was trapped within the lumen of the liposomes.

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.

Liver-like alkaline phosphatase in the tissue-unspecific type enzyme found in rabbit organs

Rabbit liver and kidney tissues are known to produce an intestinal-like alkaline phosphatase (IAP-like enzyme) as a dominant isozyme, with a minor isozyme of tissue-unspecific type (UAP), unlike humans and other mammalians. We investigated immunohistochemically and biochemically these unique isozymes in the rabbit liver and bone, and compared them with the human isozyme. In rabbit liver, UAP was found to be localized only in the apical part of the membrane of cells lining the bile duct, whereas IAP-like enzyme was found in the sinusoidal membrane of hepatocytes. Rabbit liver UAP was separated from IAP-like enzyme by DEAE-cellulose column chromatography. Rabbit bone tissue contained only one UAP isozyme. The two UAPs were biochemically and physicochemically compared with human liver AP. Both UAPs reacted with an anti-human liver AP monoclonal antibody, not with an anti-human bone AP monoclonal antibody, indicating that both enzymes have the same antigenicity as human liver AP. Rabbit liver and bone UAPs had similar N-linked sugar-chain heterogeneities to the respective human enzymes. In addition, rabbit bone AP also had an O-linked sugar chain, as did human bone AP, unlike rabbit and human liver APs.

Purification and partial characterization of intestinal-like alkaline phosphatase in rabbit kidney

Two types of alkaline phosphatase (AP) isozymes in rabbit kidney, a major intestinal-like type and a minor tissue-unspecific type, have been identified. The former enzyme was purified from rabbit kidney by immunoaffinity chromatography using monoclonal anti-human intestinal AP antibody. The purified enzyme yielded a single protein band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the apparent molecular size of its monomer subunit was found to be 72,000. Three amino acid residues within the first 16 N-terminal amino acid residues were different in purified AP and human intestinal AP. Although the rabbit enzyme possessed some peptide bands identical to those of human adult intestinal AP after Staphylococcus aureus V8 protease digestion, the enzyme did not react with monoclonal antibody against human adult intestinal AP alone, whereas it did react with monoclonal antibody against both human adult and fetal intestinal APs. The affinity of the enzyme for concanavalin A was identical to that of the fetal intestinal AP, but different from that of the adult enzyme. These results indicate that the antigenicity and certain properties of purified rabbit AP are more like those of human fetal intestinal AP or Kasahara isozyme, so-called intestinal-like AP, than like human adult intestinal AP.

Developmental changes in the antigenicity and sugar-chain heterogeneity of rabbit alkaline phosphatases

1. Rabbit alkaline phosphatases (APs) clearly fused with the anti-human AP antibodies. In particular, fetal liver and kidney APs reacted slightly less with the anti-intestinal AP antibody as did adult enzymes, suggesting that intestinal AP-like isozyme is expressed at earlier stages of gestation in rabbit liver and kidney. 2. Immunohistochemical data indicated that intestinal AP-like isozyme in the kidney was mainly localized in the distal convoluted tubules and slightly in the proximal straight tubules, whereas liver/bone/kidney AP-like enzyme was found more in the glomeruli and interstitial capillary walls as a major component. 3. The sugar-chain heterogeneity of adult and fetal rabbit APs displayed organ-specificity as did of rat and human APs. Moreover, in fetal development, the expression of high-mannose type or hybrid type sugar chains precedes the expression of complex type sugar chains in fetal development.