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PubMed1989

Pyridoxal phosphate as a probe of the cytoplasmic domains of transmembrane proteins: application to the nicotinic acetylcholine receptor.

A novel procedure has been developed to specifically label the cytoplasmic domains of transmembrane proteins with the aldehyde pyridoxal 5-phosphate (PLP). Torpedo californica acetylcholine receptor (AcChR) vesicles were loaded with [3H]pyridoxine 5-phosphate ([3H]PNP) and pyridoxine-5-phosphate oxidase, followed by intravesicular enzymatic oxidation of [3H]PNP at 37 degrees C in the presence of externally added cytochrome c as a scavenger of possible leaking PLP product. The resulting Schiff's bases between PLP and AcChR amino groups were reduced with NaCNBH3, and the pyridoxylated proteins were analyzed by fluorography. The four receptor subunits were labeled whether the reaction was carried out on the internal surface or separately designed to mark the external one. On the other hand, the relative pyridoxylation of the subunits differed in both cases, reflecting differences in accessible lysyl residues in each side of the membrane. Proteinase K treatment of labeled AcChR vesicles generated a peptide of 13 kDa that could be detected with anti-PLP antibodies only when the pyridoxylation was carried out on the internal surface of the vesicles. Even though there are no large differences in the total lysine content among the subunits and there are two copies of the alpha-subunit, internal surface labeling by PLP was greatest for the highest molecular weight (delta) subunit, reinforcing the concept that the four receptor subunits are transmembranous and may protrude into the cytoplasmic face in a fashion [Strader, C. D., & Raftery, M. A. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 5807-5811] that is proportional to their subunit molecular weight.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed2004

Pyridoxal phosphate and hepatocyte growth factor prevent dialysate-induced peritoneal damage.

Glucose-based peritoneal dialysate (PD) is responsible for increased accumulation of advanced glycation end products (AGE) in the peritoneum of continuous ambulatory peritoneal dialysis patients. Pyridoxal 5'-phosphate (PLP), a derivative of vitamin B(6), protects proteins from glycation. Hepatocyte growth factor (HGF) heals damaged tissues in a reciprocal manner against TGF-beta1. First, with the use of gas chromatography-mass spectrometry, whether PLP traps 3-deoxyglucosone (3DG), a major glucose degradation product in PD, was determined. Then, whether rat peritoneal tissue damages induced by intraperitoneal administration of glucose-based PD is ameliorated by PLP or HGF was examined. In vitro incubation with PLP markedly decreased concentration of 3DG in a dose-dependent manner, demonstrating the 3DG-trapping effect of PLP. The peritoneum of PD-treated rats was significantly thickened compared with that of physiologic saline-treated rats. Both PLP and HGF prevented the thickening of rat peritoneum induced by PD and ameliorated accumulation of AGE and expression of TGF-beta1, vascular endothelial growth factor, and type 1 collagen and a number of blood vessels. Furthermore, expression of HGF was significantly increased in the peritoneum of PLP-treated rats compared with that of PD-treated rats. In conclusion, PLP shows 3DG-trapping effect. PLP and HGF prevented peritoneal thickening; accumulation of AGE; expression of TGF-beta1, vascular endothelial growth factor, and type 1 collagen; and neoangiogenesis in rat peritoneum induced by PD.

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PubMed1980

Three-dimensional structure of a pyridoxal-phosphate-dependent enzyme, mitochondrial aspartate aminotransferase.

X-ray diffraction studies to 2.8-A resolution have yielded the three-dimensional structure of mitochondrial aspartate aminotransferase (L-aspartate:2-oxoglutarate aminotransferase, EC 2.6.1.1), an isologous alpha 2 dimer (Mr = 2 x 45,000). The subunits are rich in secondary structure and contain two domains, one of which anchors the coenzyme, pyridoxal 5'-phosphate. Each active site lies between the subunits and is composed of residues from both of them.

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