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)

Insulin influences certain metabolic and transport renal functions and is avidly degraded by the kidney, but the relative contribution of the luminal and basolateral tubular membranes to these events remains controversial. We studied (125)I-insulin degradation [TCA and immunoprecipitation (IP) methods] and the specific binding of the hormone by purified luminal (L) and basolateral (BL) tubular membranes. These were prepared from rabbit kidney cortical homogenates by differential and gradient centrifugation and ionic precipitation steps in sequence, which resulted in enrichment vs. homogenate of marker enzymes' activities (sodium-potassium-activated adenosine triphosphatase for BL and maltase for L) of 8- and 12-fold, respectively. Both fractions degraded insulin avidly and bound the hormone specifically without saturation even at pharmacologic concentrations (10 muM). At physiologic insulin concentrations (0.157 nM) BL membranes degraded substantial amounts of insulin (44.2+/-2.6 and 40.7+/-2.2 pg/mg protein per min by the TCA and IP methods, respectively), even though at lesser rates (P < 0.001) than the luminal fraction (67.2+/-2.3 and 75+/-6.2 pg/mg protein per min, respectively); the rate of insulin catabolism by BL membranes was significantly higher (P < 0.001) than that which could be attributed to their contamination by luminal components [12.2+/-1.9 pg/mg per min (TCA method), or 13.7+/-1.9 pg/mg per min (IP method)]. Competition experiments suggested that insulin-degrading activity in both fractions includes both specific and nonspecific components. In contrast to degradation, insulin binding by both membranes was highly specific for native insulin and was severalfold higher in BL than L membranes [17.5+/-1.3 vs. 4.5+/-0.4 fmol/mg protein (P < 0.001) at physiologic insulin concentrations]. Despite the marked difference in the binding capacity for insulin by the two membranes, the patterns of labeled insulin displacement by increasing amounts of unlabeled hormone were superimposable (50% displacement required approximately 3 nM), suggesting that their receptors' affinity for insulin was similar. These observations provide direct evidence that interaction of insulin with the kidney involves binding and degradation of the hormone at the peritubular cell membrane.
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PMID:Insulin binding and degradation by luminal and basolateral tubular membranes from rabbit kidney. 704 Apr 74

Protein secretion in yeast is generally associated with a burden to cellular metabolism. To investigate this metabolic burden in Schizosaccharomyces pombe, we constructed a set of strains secreting the model protein maltase in different amounts. We quantified the influence of protein secretion on the metabolism applying (13)C-based metabolic flux analysis in chemostat cultures. Analysis of the macromolecular biomass composition revealed an increase in cellular lipid content at elevated levels of protein secretion and we observed altered metabolic fluxes in the pentose phosphate pathway, the TCA cycle, and around the pyruvate node including mitochondrial NADPH supply. Supplementing acetate to glucose or glycerol minimal media was found to improve protein secretion, accompanied by an increased cellular lipid content and carbon flux through the TCA cycle as well as increased mitochondrial NADPH production. Thus, systematic metabolic analyses can assist in identifying factors limiting protein secretion and in deriving strategies to overcome these limitations.
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PMID:Overcoming the metabolic burden of protein secretion in Schizosaccharomyces pombe--a quantitative approach using 13C-based metabolic flux analysis. 2426 98