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

---

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

The GTP-binding subunit of transducin (T alpha) activates the cGMP phosphodiesterase (PDE) of bovine retinal rods by relieving the constraint imposed by the inhibitory subunit PDE gamma. We have isolated and characterized the complex T alpha.GTP gamma S-PDE gamma formed when T alpha is activated by the nonhydrolyzable analog GTP gamma S. Sedimentation and light-scattering techniques demonstrate that, in contrast to free T alpha.GTP gamma S, which is soluble, the T alpha.GTP gamma S-PDE gamma complex, as well as T alpha.GTP-PDE gamma, is membrane bound at cytosolic ionic strength. It is eluted from the membrane at low ionic strength as a monomeric and 1:1 stoichiometric complex. The relative affinities of PDE gamma for PDE alpha beta and for T alpha.GTP are discussed.
...
PMID:Activation of retinal rod cyclic GMP-phosphodiesterase by transducin: characterization of the complex formed by phosphodiesterase inhibitor and transducin alpha-subunit. 283 63

Light activation of GTP binding to G-protein and its eventual hydrolysis are hypothesized to lead to activation and inactivation of cGMP phosphodiesterase (PDE) in vertebrate rod disk membranes (RDM). However, the reported GTPase rate of 3 per minute is too slow to account for the observed rapid inactivation of PDE. Our investigations on GTPase activity showed that RDM isolated in the dark have considerable dark GTPase activity, which is enhanced by light. In dark and light, the enzyme exhibits biphasic substrate dependence with two Km's for GTP of 2-3 and 40-80 microM at 22 degrees C and less than 1 and 10-25 microM at 37 degrees C. The Km's were not influenced by light. On the basis of G-protein content of the RDM, the Vmax's for the two activities at 37 degrees C in light are 4-5 and 20-30 GTPs hydrolyzed per minute per G-protein. RDM washed free of soluble and peripheral proteins do not have measurable GTPase activity in the dark or light. Purified G-protein alone also did not turn over GTP, apparently because bleached rhodopsin is required for it to bind GTP. Reconstitution of washed membranes with purified G-protein restores both the low- and high-Km GTPase activities. Inactivation of G-protein as measured by PDE turnoff and dissociation signal recovery is found to be faster at higher than lower [GTP], consistent with the observation that the higher GTPase activity associated with the higher Km alos resides in the G-protein.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Contribution of the guanosinetriphosphatase activity of G-protein to termination of light-activated guanosine cyclic 3',5'-phosphate hydrolysis in retinal rod outer segments. 284 43

The target proteins for arrestin (48 kDa protein) action during the quench of cGMP phosphodiesterase (PDE) activation in retinal rod disk membranes were identified by the use of a cross-linking reagent. A heterobifunctional, cleavable, photo-activatable cross-linker (sulfo-SADP) was coupled to purified arrestin. Under precise weak visible light bleach and nucleotide conditions of quench, the cross-linker was UV flash-activated at a time when quench was well established. The target proteins covalently linked to arrestin by cross-linker activation were identified by immunoblotting. In the presence of ATP arrestin cross-linked to both PDE and rhodopsin during the quench phenomenon. Removal of ATP from the reaction mixture essentially abolished the cross-link with PDE, just as ATP omission abolishes quench, but significantly increased the cross-link to rhodopsin. The absence of a cross-link to the plentiful beta-subunit of transductin, as well as the results of competition studies employing arrestin without attached cross-linker, suggest that the observed cross-links are specific and reflect true binding interactions of arrestin during quench. The data are consistent with a model of quench in which photolyzed rhodopsin (R*) catalyzes the formation of an activated form of arrestin, which dissociates from R* in the presence of ATP, and binds to PDEs, thereby deactivating them.
...
PMID:Sites of arrestin action during the quench phenomenon in retinal rods. 284 5

The exchange-inert Cr(III) beta, gamma-bidentate guanine nucleotide complexes Cr(III)GTP and Cr(III)Gpp(NH)p were used to probe the role of transducin in activating the retinal cGMP cascade. The Cr(III) nucleotide complexes were found to have lower binding affinity for transducin as compared to the Mg2+ complexes. However, the rate of hydrolysis of the transducin-bound Cr(III)GTP was similar to that of Mg(II)GTP. Cr(III)Gpp(NH)p activated the cGMP phosphodiesterase of photolyzed rod outer segment membranes up to 75% of the Mg(II)Gpp(NH)p level but lacked the ability to dissociated the transducin subunits from the rod outer segment membrane. This result implies that the activation of the phosphodiesterase by transducin-GTP complex is a membrane-associated event and the formation of a soluble complex of transducin-GTP with the inhibitory peptide of the phosphodiesterase may not be an obligatory step. Both the delta and lambda screw sense stereoisomers of Cr(III)Gpp(NH)p were capable of activating the cGMP cascade with no apparent stereoselectivity. The nature of the interaction of the metal ion and GTP at the nucleotide-binding site of transducin is discussed together with the results from previous studies using the phosphorothioate GTP analogues [Yamanaka, G., Eckstein, F., & Stryer, L. (1985) Biochemistry 24, 8094-8101] and is compared to the site found in homologous GTP-binding proteins such as elongation factor Tu [Jurnak, F. (1985) Science (Washington, D.C.) 230, 32-36; la Cour, T.F.M., Nyborg, J., Thirup, S., & Clark, B.F.C. (1985) EMBO J. 4, 2385-2388]. The implications of the observed results on the molecular mechanism of visual signal transduction are discussed.
...
PMID:Chromium(III) beta, gamma-bidentate guanine nucleotide complexes as probes of the GTP-activated cGMP cascade of retinal rod outer segments. 285 56

We have demonstrated previously that atrial natriuretic factor (ANF) augments urinary, plasma and kidney cGMP levels but has no significant effect upon cAMP. Using cGMP as a marker, we searched for specific target sites involved in the action of ANF in the dog kidney, and observed no change of cGMP in the proximal tubules, a 2-fold increase over basal levels in the thick loop of Henle and a 3-fold elevation in the collecting duct. The most striking action on cGMP occurred in the glomeruli with a rise of up to 50-fold being evident at 1-2 min. after the addition of ANF. The results obtained in the absence or presence of a phosphodiesterase inhibitor support the notion that the effects of ANF were exerted at the level of guanylate cyclase stimulation rather than cGMP phosphodiesterase inhibition. The action of sodium nitroprusside (SNP), a direct stimulator of soluble guanylate cyclase, differed from that of ANF. The ability of the factor to enhance cGMP levels was correlated with the distribution of particulate guanylate cyclase. This study identifies the glomeruli and the distal part of the nephron as specific targets of ANF and implicates particulate guanylate cyclase as the enzyme targetted for the expression of its action.
...
PMID:The increase of cGMP by atrial natriuretic factor correlates with the distribution of particulate guanylate cyclase. 285 57

Cyclic GMP metabolism has been investigated in the retinas of mice that are heterozygous for a 'photoreceptor dystrophy' gene and have a lowered concentration of cGMP in their photoreceptor cells. The concentration of rhodopsin, retinal morphology and guanylate cyclase kinetics were normal. Cyclic GMP phosphodiesterase had a lowered affinity for cGMP. In accord with previous observations, chelation of exogenous calcium had no effect on cGMP levels in light-adapted retinas but increased them in dark-adapted tissue. The difference between cGMP concentrations in heterozygous and normal retinas in the dark was then eliminated. It was concluded that a modulator of cGMP phosphodiesterase activity is most likely to be causing the lowered steady-state level of cGMP in heterozygous retinas and that calcium is not involved.
...
PMID:Cyclic GMP in the retinas of normal mice and those heterozygous for early-onset photoreceptor dystrophy. 286 61

In the membranous signal transduction process, hormone-binding to receptors causes receptor interaction with signal-transducing components; these components transfer the stimulus to effector systems, which generate intracellular signals. Several guanine nucleotide-binding proteins (N- or G-proteins) have been identified as membranous signal-transducing components. Two N-proteins are involved in the hormonal regulation of adenylate cyclase activity, one of which being stimulatory (Ns), the other one being inhibitory (Ni). Ns, Ni and a third N-protein, No, whose function is unknown, occur ubiquitously. On the other hand, transducin, an N-protein, which functionally couples light-activated rhodopsin to a cGMP phosphodiesterase, is specific for the retina. In addition to their established role as transducers regulating adenylate cyclase and retinal cGMP phosphodiesterase, N-proteins proteins may be involved in two mechanisms by which the cytoplasmic calcium concentration is elevated, i.e. hormonal stimulation of a phospholipase C catalyzing phosphatidyl-inositol 4,5-diphosphate hydrolysis (Pi response) and hormone-induced opening of receptor-operated calcium channels; the membrane-bound forms of cAMP phosphodiesterase and guanylate cyclase, stimulated by insulin and atrial natriuretic factor, respectively, are also likely to be regulated via N-proteins. Guanine nucleotide-binding proteins appear to play a universal role in transmembranous signalling processes, controlling effector systems (i.e. enzymes and ion channels) that regulate cytoplasmic concentrations of intracellular messengers such as cyclic AMP, cyclic GMP and calcium.
...
PMID:[Principles of transmembranous signal transduction in the action of hormones and neurotransmitters]. 286 63

Like retinal rods, cone photoreceptors contain cyclic GMP and light-activated phosphodiesterase. The cGMP phosphodiesterase cascade is thought to mediate phototransduction in rods. Biochemical assays of nucleotide content in cone-dominant retinas, however, have failed to demonstrate light-induced changes in cGMP. Changes in cyclic AMP following light exposure have been reported, leading to the suggestion that in cone phototransduction cAMP assumes a role analogous to that played by cGMP in rods. Cyclic GMP introduced from tight-seal pipettes into isolated cones of the larval tiger salamander, Ambystoma tigrinum, rapidly increases light-modulated membrane current more than 10-fold. In cones, as in rods, cGMP also causes an approximately 10-fold increase in photocurrent duration and a 5- to 10-fold increase in light-sensitivity. Cyclic AMP has no effect on cone photocurrents under the same conditions. Because cGMP has similar effects on photocurrent magnitude and kinetics in both rods and cones, we conclude that cGMP plays corresponding roles in transduction in both vertebrate photoreceptor classes.
...
PMID:Cyclic GMP increases photocurrent and light sensitivity of retinal cones. 299 15

Cyclic nucleotide phosphodiesterase activities in human neutrophils were characterized. Neutrophil sonicates exhibited high-affinity and low-affinity cAMP phosphodiesterase activities, with apparent Km values of 1.9 microM and 112 microM, respectively. No cGMP phosphodiesterase activity was detected. Approx. 70% of cAMP phosphodiesterase activity measured at 1 microM cAMP was present in the soluble subcellular fraction, and the remainder was localized in the particulate fraction. Chromatography of the soluble subcellular fraction on DE-52 ion-exchange resin yielded a low-affinity cAMP phosphodiesterase activity and a high-affinity cAMP phosphodiesterase activity. The soluble high-affinity cAMP phosphodiesterase activity exhibited moderate calmodulin sensitivity. After incubation of intact neutrophils with N-formylmethionylleucylphenylalanine (fMet-Leu-Phe), a 25-30% increase in the activity of the high-affinity cAMP phosphodiesterase activity was observed in the sonicate and in the soluble fraction. Maximal increases were achieved after 2 min of incubation and the increases persisted for at least 10 min. The increase in activity was independent of calmodulin and guanine nucleotide regulatory proteins. These results indicate that a soluble high-affinity cAMP phosphodiesterase comprises the majority of phosphodiesterase activity in neutrophils and that increases in this activity may contribute to the regulation of cAMP levels in neutrophils during activation.
...
PMID:Characterization of cyclic-nucleotide phosphodiesterase activities in resting and N-formylmethionylleucylphenylalanine-stimulated human neutrophils. 300 3

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.
...
PMID:Characterization of the light-induced increase in the Michaelis constant of the cGMP phosphodiesterase in frog rod outer segments. 300 80


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---