Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P56851 (epididymal)
 11,273 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The sensitivity of rat epididymal-adipose-tissue pyruvate dehydrogenase phosphate phosphatase, NAD+-isocitrate dehydrogenase and 2-oxoglutarate dehydrogenase to Ca2+ ions was studied both in mitochondrial extracts and within intact coupled mitochondria. It is concluded that all three enzymes may be activated by increases in the intramitochondrial concentration of Ca2+ and that the distribution of Ca2+ across the mitochondrial inner membrane is determined, as in rat heart mitochondria, by the relative activities of a uniporter (which transports Ca2+ into mitochondria and is inhibited by Mg2+ and Ruthenium Red) and an antiporter (which allows Ca2+ to leave mitochondria in exchange for Na+ and is inhibited by diltiazem). Previous studies with incubated fat-cell mitochondria have indicated that the increases in the amount of active non-phosphorylated pyruvate dehydrogenase in rat epididymal tissue exposed to insulin are the result of activation of pyruvate dehydrogenase phosphate phosphatase. In the present studies, no changes in the activity of the phosphatase were found in extracts of mitochondria, and thus it seemed likely that insulin altered the intramitochondrial concentration of some effector of the phosphatase. Incubation of rat epididymal adipose tissue with medium containing a high concentration of CaCl2 (5mM) was found to increase the active form of pyruvate dehydrogenase to much the same extent as insulin. However, the increases caused by high [Ca2+] in the medium were blocked by Ruthenium Red, whereas those caused by insulin were not. Moreover, whereas the increases resulting from both treatments persisted during the preparation of mitochondria and their subsequent incubation in the absence of Na+, only the increases caused by treatment of the tissue with insulin persisted when the mitochondria were incubated in the presence of Na+ under conditions where the mitochondria are largely depleted of Ca2+. It is concluded that insulin does not act by increasing the intramitochondrial concentration of Ca2+. This conclusion was supported by finding no increases in the activities of the other two Ca2+-responsive intramitochondrial enzymes (NAD+-isocitrate dehydrogenase and 2-oxoglutarate dehydrogenase) in mitochondria prepared from insulin-treated tissue compared with controls.
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PMID:Role of Ca2+ ions in the regulation of intramitochondrial metabolism in rat epididymal adipose tissue. Evidence against a role for Ca2+ in the activation of pyruvate dehydrogenase by insulin. 632 51

1. Increasing concentrations of both Ca2+ and Sr2+ (generated by using EGTA buffers) resulted in 4-fold increases in the initial activity of pyruvate dehydrogenase within intact uncoupled mitochondria from rat epididymal adipose tissue incubated in the presence of the ionophore A23187, ATP, Mg2+ and oligomycin. The k0.5 values (concentrations required for half-maximal effects) for Ca2+ and Sr2+ were 0.54 and 7.1 microM respectively. In extracts of the mitochondria, pyruvate dehydrogenase phosphate phosphatase activity was stimulated about 4-fold by Ca2+ and Sr2+, with k0.5 values of 1.08 and 6.4 microM respectively. 2. NAD+-isocitrate dehydrogenase and oxoglutarate dehydrogenase appeared to be rate-limiting in the oxidation of threo-Ds-isocitrate and oxoglutarate by uncoupled mitochondria from brown adipose tissue of cold-adapted rats. Ca2+ (and Sr2+) diminished the Km for the oxidation of both threo-Ds-isocitrate and oxoglutarate. The kinetic constants for these oxidations were very similar to those obtained for the activities of NAD+-isocitrate dehydrogenase and oxoglutarate dehydrogenase in extracts of the mitochondria. In particular, the k0.5 values for Ca2+ were all in the range 0.2--1.6 microM and Sr2+ was found to mimic Ca2+, but with k0.5 values about 10 times greater. 3. Overall, the results of this study demonstrate that the activities of pyruvate dehydrogenase, NAD+-isocitrate dehydrogenase and oxoglutarate dehydrogenase may all be increased by Ca2+ and Sr2+ within intact mitochondria. In all cases the k0.5 values are close to 1 and 10 microM respectively, as found for the separated enzymes. Experiments on brown-adipose-tissue mitochondria incubated in the presence of albumin suggest that it may be possible to use the sensitivity of the dehydrogenases to Ca2+ as a means of assessing the distribution of Ca2+ across the mitochondrial inner membrane.
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PMID:Role of calcium ions in the regulation of intramitochondrial metabolism. Properties of the Ca2+-sensitive dehydrogenases within intact uncoupled mitochondria from the white and brown adipose tissue of the rat. 677 77