Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.20 (alpha-glucosidase)
 4,237 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The subcellular distribution of the Na+/H+ antiporter in renal proximal tubule cells was studied with differential and density gradient centrifugation. Enzyme markers for basolateral membranes [Na+/K+)-ATPase), brush border membranes (maltase), and a variety of intracellular organelles (NADPH cytochrome c reductase, thiamine pyrophosphatase, acid phosphatase, and succinate cytochrome c reductase) were simultaneously assayed in sucrose density gradients. Basolateral membranes (median rho = 1.150) were well separated from brush border membranes (median rho = 1.165) by this technique. Markers for other cellular organelles had intermediate or bimodal distributions. To determine the cellular location of the Na+/H+ antiporter, Na+-dependent collapse of preformed pH gradients was assayed in the sucrose density gradient fractions using acridine orange. Na+/H+ antiporter activity paralleled the distribution of the brush border membrane fractions; activity in the peak basolateral membrane fraction was less than 5% of that in the peak brush border fraction. To determine whether antiporter activity was potentially detectable in all cell fractions, nigericin was added to each fraction and K+/H+ exchange was assayed with acridine orange. Activity was present in all sucrose density gradient fractions. In addition, there was no alteration in Na+/H+ exchange activity measured in brush border membranes after mixing with cell sol or basolateral membranes, showing that neither inhibitors nor activators of the Na+/H+ antiporter were present in any of the cell fractions. These controls confirmed the finding that Na+/H+ antiporter activity was absent from basolateral membranes. The presence of the Na+/H+ antiporter in brush border membranes and its absence from basolateral membranes is consistent with its playing an important role in the vectorial transport of H+ from blood to tubular lumen in the renal proximal tubule.
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PMID:Asymmetric distribution of the Na+/H+ antiporter in the renal proximal tubule epithelial cell. 631 99

A conventional brush border membrane preparation, obtained by divalent cation precipitation of homogenates of rabbit renal cortex, was analyzed by countercurrent distribution in an aqueous dextran:polyethylene glycol two-phase system. The resulting fractions were assayed for the presence of the Na+/H+ antiporter and for a variety of biochemical marker enzymes. This analysis revealed four physically distinct membrane populations (A-D). Population A consisted of two subpopulations, A' and A", which were enriched an average of 49-fold in maltase; they were also highly enriched in alkaline phosphatase, leucine aminopeptidase, and Na+/H+ antiporter. On the basis of their marker contents, populations A' and A" appear to represent highly purified, functional brush border membrane vesicles. Population B was enriched twofold in NADPH-cytochrome c reductase and population C was enriched 12-fold in galactosyltransferase. Populations B and C accounted for 25% of the protein in the starting material and appear to reflect contamination of the brush border membrane preparation by subpopulations of endoplasmic reticulum and Golgi fragments. Population D was enriched in Na+/H+ antiporter, alkaline phosphatase, leucine aminopeptidase, Na-K-ATPase, and acid phosphatase but not maltase, NADPH-cytochrome c reductase, galactosyltransferase, or succinate dehydrogenase. Its identity is unclear, and it might consist of a multiplicity of populations from different origins.
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PMID:Na+/H+ antiporter in membrane populations resolved from a renal brush border vesicle preparation. 633 Nov 75