Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.4.1 (phosphodiesterase)
18,767 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In an attempt to determine the mechanism of insulin resistance in the presence of obesity, we examined effects of insulin on insulin-sensitive phosphodiesterase (PDE) in spontaneously diabetic KK mice. Isolated fat cells prepared from epididymal adipose tissue were incubated, with or without insulin, for 10 min. In the case of subcellular fractionation, only membrane-bound PDE was activated by insulin, as was noted in the case of rat fat cells. The specific activity was decreased in KK mice compared with control C57BL/6 mice. The dose-response curve, expressed as a percent of the maximal insulin effect, shifted to the right and the increase of ED50 indicated a decreased insulin sensitivity in the KK mice. The maximal insulin effect did not change, either when expressed as a percent of the basal enzyme activity or when expressed on a per cell basis. Specific binding of [125I]-insulin in fat cells increased in KK mice and curvilinear Scatchard plots showed an increase of the high-affinity sites. These data indicate that impairment of PDE activation in fat cells of KK mice relates to postreceptor defects and the uncoupling may result in a decreased sensitivity.
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PMID:Insulin resistance of fat cells from spontaneously diabetic KK mice. Analysis of insulin-sensitive phosphodiesterase. 299 83

The basal and plus insulin states of glucose transport activity in adipocytes are known to show different responses to changes in the pH or osmolarity of the incubation mixture. When the pH was raised from 7 to 8, the basal glucose transport activity (assessed from the rate of 3-O-methyl-D-glucose uptake) was increased approximately 3-fold while the plus insulin activity remained virtually unaffected. Likewise, when cells were exposed to 300 mM sorbitol, the basal glucose transport activity, but not the plus insulin activity, was considerably increased. In both cases, the change in the transport activity was ATP-dependent and was completed in approximately 60 min. The increase in the cellular glucose transport activity was accompanied, in both cases, by an increase in the glucose transport activity in the plasma membrane fraction and a decrease in the activity in the high-speed pellet fraction. The transport activity in the subcellular fractions was determined after reconstitution into egg lecithin liposomes. Both isotonic buffer at pH 8.0 and hypertonic buffer at pH 7.4 significantly stimulated membrane-bound cAMP phosphodiesterase in adipocytes. It is concluded that the above two experimental conditions may induce insulin-like effects in fat cells and may facilitate translocation of the glucose transport activity from an intracellular site to the plasma membrane.
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PMID:Apparent translocation of glucose transport activity in rat epididymal adipocytes by insulin-like effects of high pH or hyperosmolarity. 300 96

Activation of cGMP phosphodiesterase in rod disk membrane in the light is thought to be an intermediary process of phototransduction. In various preparations of frog rod outer segments, the Michaelis constant (Km) of the phosphodiesterase was measured with pH assay method. On illumination, the Km increased from the value of the dark (130 microM) by about 8-fold (1 mM) in crude preparations, but did not change appreciably in purified disk membranes, confirming the previous finding by Robinson et al. (Robinson, P.R., Kawamura, S., Abramson, B. and Bownds, M.D. (1980) J. Gen. Physiol. 76, 631-645). The present work further showed that the light-induced Km increase is labile to various experimental manipulations such as sonication, freeze-thawing, etc. However, the Km in the light was relatively high in a crude disk membrane preparation and in a lyzed preparation. In addition, reconstitution experiments revealed that the Km increase does not require soluble components. Both proteolytic digestion and phospholipase treatment reduced the light Km of the phosphodiesterase in crude disk membranes. The above results suggest that there is a labile factor(s) responsible for the light-induced Km increase and that the factor is a membrane-bound protein and requires structural integrity of the disk membrane to exert its function. The latency of the Km increase after light stimulation was less than 2 s.
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PMID:Characterization of the light-induced increase in the Michaelis constant of the cGMP phosphodiesterase in frog rod outer segments. 300 80

Insulin acutely inhibits the catecholamine-stimulated rise in cAMP levels in fat, liver, and muscle primarily through stimulation of the enzyme cAMP phosphodiesterase (PDE). Adipocytes from rat epidydimal fat pads were exposed to insulin and fractionated by centrifugation. Whereas the cytosolic fraction contained a low-affinity cAMP PDE that was unaffected by insulin, the activity of a high-affinity enzyme residing in a particulate fraction was increased by insulin. This enzyme activity could be solubilized with nonionic detergent and chromatographed on ion exchange followed by chromatofocusing. The resulting enzyme preparation was subjected to sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. Silver staining revealed a single band with a molecular weight of 60,000. This apparent molecular weight was verified by calculation of the hydrodynamic properties of the enzyme. Evaluation of its kinetic properties indicated that the enzyme activity residing in this solubilized 60,000-Mr protein exhibited lower affinity than the membrane-bound enzyme but was still specific for cAMP. Activation of this enzyme may be one of the primary mechanisms by which insulin counteracts the effects of adenylate cyclase-stimulating hormones.
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PMID:Purification of putative insulin-sensitive cAMP phosphodiesterase or its catalytic domain from rat adipocytes. 301 73

Some biochemical and pharmacological properties of a novel, potent inhibitor of cyclic AMP phosphodiesterase, N-cyclohexyl-N-methyl-4-(7-oxy-1,2,3,5-tetrahydroimidazo[2,1-b] quinazolin-2-one) butyramide (RS-82856), were investigated. RS-82856 selectively inhibits the high affinity form of cyclic AMP phosphodiesterase (type IV) isolated from human platelets (Ki = 0.5 nM) with only weak effects on both the nonspecific and cyclic GMP-sensitive phosphodiesterases. The inhibitor reduces both maximum velocity and substrate affinity of the type IV enzyme. This mixed pattern of partial competitive and noncompetitive inhibition was also obtained with one of the two high affinity forms of phosphodiesterase found in dog heart (Ki = 0.75 nM). Of several human and dog tissues examined, RS-82856 exhibits marked selectively for the platelet high affinity enzyme. It also has significant inhibitory effects on cardiac membrane-bound phosphodiesterase. RS-82856 inhibits the aggregation of human platelets in response to adenosine 5'-diphosphate (IC50 = 0.11 microM) in vitro and is active ex vivo for at least 2 hr following oral administration (10 mg/kg) to rhesus monkeys. Administration of RS-82856 to instrumented, anesthetized dogs by either intravenous or intraduodenal routes increases cardiac contractile force and reduces afterload. These data suggest that RS-82856 may be useful as an agent to increase cardiac output in the treatment of congestive heart failure.
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PMID:A potent and selective inhibitor of cyclic AMP phosphodiesterase with potential cardiotonic and antithrombotic properties. 301 20

The characteristics for the binding of the selective cAMP phosphodiesterase inhibitor and antidepressant agent rolipram to brain and peripheral organs were investigated. (+/-)-[3H]Rolipram equilibrium binding and Scatchard analysis revealed saturable, reversible, stereospecific, Mg2+-dependent and heat-sensitive binding with an apparent Hill number of 1. Binding was detected both to membrane-bound and soluble sites, with dissociation constants Kd of 1.2 and 2.4 nM, respectively, and binding site concentrations (Bmax) of 19.3 and 23.6 pmol/g rat forebrain. The (-)-enantiomer of rolipram was ca. 20 times more effective than the (+)-enantiomer in displacing (+/-)-[3H]rolipram from membranes. Rolipram bound to brain tissue of all mammalian species tested including man, while tissue from bird and fish showed less binding. Organs other than brain exhibited only negligible binding. Only specific cAMP phosphodiesterase inhibitors (ICI 63.197, Ro 20-1724) were potent competitors, while rolipram itself was inactive in a variety of receptor binding assays of neuroactive ligands. The kinetics of (-)-[3H]rolipram binding to the particulate fraction revealed a complex association and dissociation behaviour. The nature of the rolipram binding protein(s) is not clear, but the low affinity binding site evident from binding kinetics may represent a rolipram-sensitive phosphodiesterase isoenzyme also common to some peripheral organs, while the high affinity binding site(s) may be related to PDE isoenzymes more confined to the central nervous system.
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PMID:Stereospecific binding of the antidepressant rolipram to brain protein structures. 301 21

Rod outer segments (ROS) from frog retina have been purified by Percoll density gradient centrifugation, a procedure that preserves their form and intactness. One- and two-dimensional electrophoretic analysis reveals a smaller number of proteins than is observed in many cell organelles and permits quantitation of the 20 most abundant polypeptides. Rhodopsin accounts for 70% of the total protein (3 X 10(9) copies/outer segment), and approximately 70 other polypeptides are present at more than 6 X 10(4) copies/outer segment. Another 17% of the total protein is accounted for by the G-protein (3 X 10(8) copies/outer segment) that links rhodopsin bleaching and the activation of cyclic GMP phosphodiesterase (PDE). The phosphodiesterase accounts for 1.5% of the protein (1.5 X 10(7) copies/outer segment), and a 48,000-dalton component that binds to the membrane in the light accounts for a further 2.6%. The function of approximately 90% of the total protein in the outer segment is known, and two-thirds of the non-rhodopsin protein is accounted for by enzyme activities associated with cyclic GMP metabolism. The relative molar abundance of rhodopsin, G-protein, and PDE is 100:10:1. Apart from these major membrane-associated proteins, most of the other proteins are cytosolic. Thirteen other polypeptides are found at an abundance of one or more copies per 1000 rhodopsins, nine soluble and four membrane-bound, and their abundance relative to rhodopsin has been quantitated. ROS have been separated into subcellular fractions which resolve three classes of soluble, extrinsic membrane, and integral membrane proteins. A listing of the proteins that are phosphorylated and their subcellular localization is given. Approximately 25 phosphopeptides are detected, and most are in the soluble fraction. Fewer phosphorylated proteins are associated with the purified outer segments than with crude ROS. Distinct patterns of phosphorylation are associated with intact rods incubated with [32P]Pi and broken rods incubated with [gamma-32P]ATP.
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PMID:Protein complement of rod outer segments of frog retina. 302 Nov 91

An alkaline 5'-nucleotidase with properties similar to those of membrane-bound 5'-nucleotidase was recovered in soluble form in the postmicrosomal supernatant fraction (cytosol) of rat liver. The enzyme seems to constitute a quantitatively distinct fraction, since the activity in postmicrosomal supernatants was increased by a further 10% by additional homogenization of livers. Lysosomal acid phosphatase activity increased similarly, whereas other membrane-bound marker enzymes alkaline phosphatase, phosphodiesterase I and glucose-6-phosphatase showed no increase when homogenization of liver tissue was continued. Gel-permeation chromatography and pH-dependence studies indicated that enzyme activity in the supernatant fraction with 0.3 mM-UMP or -AMP as substrate at pH 8.1 was about 85 or 100% specific respectively. In regenerating liver the enzyme recovered in soluble form showed decreased specific activity, in contrast with alkaline phosphatase measured for comparison. The nucleotidase activity per mg of cytosolic protein was 2.1 nmol/min with AMP as substrate. The total activity measured in the postmicrosomal supernatant was 1.5% of the homogenate activity measured in the presence of detergent.
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PMID:The presence and activity in normal and regenerating rat liver postmicrosomal supernatant fraction of an enzyme with properties similar to those of membrane-bound 5'-nucleotidase. 302 68

For clarification of the beneficial effects of the extract of Ginkgo biloba (EGB) on triethyltin (TET) toxicity in rats, the phosphodiesterase (PDE) activities of the cerebral tissue were measured under in vitro and ex vivo conditions. Under in vitro conditions, low concentrations of EGB (0.25-4.0 mg/L) activated the enzyme, whereas after higher concentrations (5-250 mg/L), dose-dependent inhibition of the enzyme activity was observed. In the lower concentration range, the extract also partially restored the high-affinity PDE activity (measured with 0.25 microM cyclic AMP) of the particulate fraction of the brain inhibited by TET in vitro. In contrast, the inhibitory influence of TET on the low-affinity PDE activity (measured with 50 microM cyclic AMP) of the particulate fraction was enhanced by the extract. Although treatment with a single large dose of EGB lowered the particulate PDE activities of the brain of normal rats, no effects of the extract could be detected in animals after repeated daily administrations of EGB during a 4-day period. Curative treatment of the TET-intoxicated rats with EGB during a 7-day period accelerated the recovery of the edematous state of the white matter caused by the intoxication and also normalized the lowered PDE activity of the particulate fraction of the edematous brain tissue. Furthermore, when preventively administered, EGB counteracted both the edema formation and the fall in PDE activity observed with treatment by TET alone. These observations strongly suggest that some beneficial effects of EGB might be due to its modulating influences on cellular cyclic AMP levels via activation of membrane-bound PDE.
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PMID:Effects of an extract of Ginkgo biloba on the 3',5'-cyclic AMP phosphodiesterase activity of the brain of normal and triethyltin-intoxicated rats. 303 90

In Dictyostelium, extracellular cAMP interacts specifically with cell-surface receptors to promote the accumulation of a variety of intracellular second messengers, such as 3'-5' cyclic adenosine monophosphate (cAMP) and 1,4,5 inositol trisphosphate (IP3). We and others have shown that activation of the cell-surface cAMP receptor can also modulate the expression of the Dictyostelium genome during development. In at least one instance, synthesis of intracellular cAMP is required for appropriate gene regulation. However, the induction of most cAMP-dependent gene expression can occur in the absence of receptor-mediated activation of adenylate cyclase and a consequent accumulation of intracellular cAMP. These results suggest that other intracellular second messengers produced in response to receptor activation may potentially act as signal transducers to modulate gene expression during development. In vertebrate cells, IP3 and diacylglycerol (DAG) are intracellular activators of specific protein kinases; they are produced in equimolar amounts by cleavage of phosphoinositol bisphosphate after a receptor-mediated activation of a membrane-bound phosphodiesterase. IP3 and, thus, by inference, diacyl-glycerol are synthesized in Dictyostelium as a response to cAMP interacting with its cell-surface receptor. Using defined conditions to inhibit the accumulation of extracellular cAMP, we have examined the effects of these compounds on the expression of genes that require cAMP for their maximal expression. Our results suggest that intracellular IP3 and DAG may in part mediate the action of extracellular cAMP on the expression of the Dictyostelium genome.
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PMID:Regulation of gene expression by the intracellular second messengers IP3 and diacylglycerol. 326 90


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