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:4.6.1.1 (adenylate cyclase)
19,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Earlier studies have shown increased adenylate cyclase (AC) activity in epididymal mouse sperm incubated under capacitating conditions in vitro. The present study investigated the effect on AC activity of excluding calcium and/or glucose from the sperm incubation medium, which would modulate expression of fertilizing potential. AC activity was higher in sperm incubated for 120 than 30 min, and was higher in sperm incubated in calcium-containing than calcium-free media for all except acrosome-reacted populations. Calcium added at the time of assay stimulated AC activity, the degree of this response being independent of the functional state of the sperm population. The guanine nucleotide analogue Gpp(NH)p slightly enhanced AC activity, but did not alter the stimulatory effect of calcium. Since calcium can increase AC activity, possibly by interaction with a divalent cation allosteric site on the catalytic subunit of the enzyme, a rise in intracellular calcium levels during capacitation may mediate the increased activity of AC, allowing expression of cAMP dependent events which are a prerequisite for fertilization.
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PMID:Adenylate cyclase activity of mouse sperm during capacitation in vitro: effect of calcium and a GTP analogue. 374 87

The adenylate cyclase of mammalian spermatozoa shares some of the properties of the isolated catalytic component from somatic cell adenylate cyclases. One of these properties is the large apparent stimulation by Mn2+. We have used the direct linear plot according to Eisenthal and Cornish-Bowden to explore whether this apparent stimulation is due to direct stimulation by Mn2+ or due to complexation of free ATP, a postulated inhibitor of cyclase activity. We have observed the activity of the particulate adenylate cyclase from bovine caudal epididymal spermatozoa as a function of calculated equilibrium values for the concentrations of Mn2+, free ATP, and the enzyme's substrate, the manganese-ATP complex. Direct linear plots for activity and substrate concentration over the apparent inhibitory concentration range of free ATP give the pattern expected for a hyperbolic substrate response. By contrast, direct linear plots in which Mn2+ concentration varies over its apparent stimulatory range show that as Mn2+ concentration increases, activities are higher than would be predicted for a hyperbolic substrate response. We conclude that for particulate bovine sperm adenylate cyclase, free ATP is not strongly inhibitory, and Mn2+ is a positive effector, reaching half-maximal stimulation at 0.2 mM. The unique nature of the sperm adenylate cyclase and its possible regulation by Mn2+ under physiological conditions is discussed.
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PMID:Manganese and manganese-ATP interactions with bovine sperm adenylate cyclase. 394 88

Using an isolated rat epididymal adipocyte system we have studied the development of tolerance to and cross-tolerance between nicotinic acid, 5-methylpyrazole-3-carboxylic acid and pyridyl-3-tetrazole. Preincubating isolated adipocytes with any one of these compounds results in a reduction of the antilipolytic activity of that compound when the cells are exposed to a subsequent challenge dose. Furthermore, preincubation with nicotinic acid, 5-methylpyrazole-3-carboxylic acid or pyridyl-3-tetrazole results in a reduction of the antilipolytic response to challenge with either of the other two compounds. Preincubation of isolated adipocytes with nicotinic acid does not affect the subsequent antilipolytic activity of the PGE2 analogue, sulprostone. Preincubation with sulprostone does not lead to the development of tolerance to its own antilipolytic actions. The results obtained from these studies suggest that nicotinic acid, 5-methylpyrazole-3-carboxylic acid and pyridyl-3-tetrazole exert their antilipolytic activity via a common biochemical pathway which is distinct from that mediating the antilipolytic activity of prostaglandins. These findings also indicate that the development of tolerance occurs prior to the involvement of adenylate cyclase in lipolysis.
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PMID:The development of tolerance to antilipolytic agents by isolated rat adipocytes. 396 29

The number of fat cells contained in the rat epididymal fat pad was found to increase rapidly as the rats grew to a weight of about 300 g. Additional increases in cell number above this weight were minimal. By contrast, cell size, as measured by the amount of triglyceride per cell, increased linearly until the rats reached about 600 g. Glycerol release per 10(6) cells in response to norepinephrine in vitro was observed to be independent of cell size. Basal release expressed in this manner showed a slight but significant positive correlation with increasing cell size. When the rate of lipolysis was based either on the amount of triglyceride in the incubation medium, as is the usual custom, or on the cell surface area, lipolysis was inversely related to cell size. In addition to these observations on lipolysis, it was also demonstrated that norepinephrine-activated adenyl cyclase activity expressed per 10(6) cells was unaffected by cell size. This leads to the suggestion that the number of adrenergic receptors in the fat cell is fixed and is independent of the size of the cell; as the cell enlarges, these receptors are merely distributed over a greater surface area.
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PMID:Lipolytic response and adenyl cyclase activity of rat adipocytes as related to cell size. 436 45

Capillaries were isolated from epididymal fat, and a catecholamine-sensitive adenylate cyclase found in these capillaries was characterized. The effect of various hormones on the accumulation of adenosine 3':5'-cyclic monophosphate in capillary endothelial cells was determined and the cyclase was found to exhibit mixed alpha and beta characteristics. Cyclase was cytochemically localized in these endothelial cells with 5'-adenylyl-imidodiphosphate as a specific cyclase substrate and alloxan as a specific cyclase inhibitor. Lead imidodiphosphate was precipitated at or near the site of cyclase activity upon hydrolysis of 5'-adenylyl-imidodiphosphate by cyclase. This reaction product was observed primarily on the luminal surface of intact capillaries, in micropinocytic invaginations, in free vesicles within the cytoplasm, and in the intracellular junctions.
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PMID:Biochemical characterization and cytochemical localization of a catecholamine-sensitive adenylate cyclase in isolated capillary endothelium. 456 6

The activities of several pivotal nucleotide metabolizing enzymes from the testis and vasal sperm of rats treated for 7 wk with 0, 20 or 30 mg X kg X day gossypol acetic acid were examined. Total testicular lactate dehydrogenase (LDH) activity increased 40% above control in the highest treatment group examined. However, the specific activity of the testis-specific isozyme of LDH, LDH-C4, decreased to 50 and 20% of control in the 20 and 30 mg X kg X day treatment groups, respectively. Basal soluble adenylate cyclase from a 100,000 X g supernatant of testis homogenate exhibited a 25% decrease in activity only in the 30-mg treatment group. Basal adenylate cyclase activity in the testicular membrane fraction increased 20 to 30% above control in response to gossypol administration. Testis membranes from the 20- and 30-mg treatment group exhibited a 2- and 4-fold greater activation of adenylate cyclase by guanine nucleotides. In vitro dose-response curves showed a half-maximal inhibitory concentration (IC50) for inhibition of soluble testicular adenylate cyclase by gossypol of 400 microM in each treatment group. Caudal epididymal sperm adenylate cyclase activity decreased to 25% of control levels in gossypol-treated animals, and the in vitro sensitivity of the enzyme to the inhibitory effects of gossypol increased 4-fold. IC50 values for gossypol inhibition of sperm adenylate cyclase decreased from 200 microM in control animals to 75 and 50 microM in the 20 and 30 mg X kg X day treatment groups, respectively. Cyclic adenosine 3':5' monophosphate phosphodiesterase activity in caudal sperm increased 6-fold in the 20- and 30-mg treatment groups. These results demonstrate that nucleotide metabolizing enzymes in sperm are major targets for the actions of gossypol and provide a possible mechanism for the inhibition of normal sperm function by this compound.
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PMID:Gossypol modulation of nucleotide metabolizing enzymes in the reproductive tract of male rats. 609 38

(1) Iterative non-linearising optimisation techniques have been used to fit three alternative models to relationships between beta-adrenergic effector concentrations and the lipolytic response which they elicit in dispersed adipocytes derived from rat epididymal fat pads. (2) The models, which consist of a simple hyperbolic relationship, a Hill-type functions and a rational quadratic formulation, were fitted to data obtained with agonists, "partial" agonists and antagonists both alone and in combination. (3) Whereas the hyperbolic relationship was inadequate in all circumstances, the hill-type function accommodated dose-response curves which exhibit no "auto-inhibitory" hook or bell-shaped feature. However, the rational quadratic function could be satisfactorily fitted to the data whether or not the auto-inhibitory phase was apparent. (4) The mechanisms that govern the steepness of the dose-response relationships and their bell-shaped feature are discussed. Evidence is presented that the latter originates at the level of adenylate cyclase.
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PMID:A kinetic analysis of the actions of L-noradrenaline and its related agonists and antagonists on in vitro lipolysis in rat adipose tissue. 612 23

Pertussis toxin (PT), a protein produced by Bordetella pertussis, was studied for its effect on lipolysis in isolated rat epididymal adipocytes. Exposure of adipocytes to pertussis toxin resulted in a significant increase in cyclic AMP levels and lipolysis after a lag of 1-2 hr. Both the maximal rate of lipolysis and the time lag (beyond 1 hr) were PT concentration-dependent. Heat treatment (95 degrees C, 30 min) or incubation with specific antibody directed against PT eliminated the ability of toxin to increase lipolysis. Cell-free culture medium from B. pertussis, but not from nontoxigenic Bordetella species, had the same effect on lipolysis as purified toxin. Comparison of the PT effect with the known lipolytic effect of cholera toxin (CT) revealed that the two toxins elicited responses that were indistinguishable in time course and magnitude. In contrast, the adenylate cyclase (EC 4.6.1.1) activities in membranes prepared from PT- or CT-treated adipocytes were different. Adenylate cyclase activity in membranes from control (untreated) adipocytes was inhibited 35-64% by the adenosine analogue N6-(L-2-phenylisopropyl)-adenosine. As expected from previous studies, membranes from CT-treated adipocytes demonstrated an increased basal activity but showed the same proportional inhibition by N6-(L-2-phenylisopropyl)-adenosine as controls. On the other hand, membranes from adipocytes exposed to PT (400 ng/ml for 4 hr) showed no increase in basal adenylate cyclase activity but had reduced sensitivity to N6-(L-2-phenylisopropyl)-adenosine inhibition, with the maximal effect ranging from 11 to 30% at 10(-6) M N6-(L-2-phenylisopropyl)-adenosine. These data support the hypothesis that PT promotes cyclic AMP-dependent lipolysis in a manner quantitatively equivalent to CT, but by a different mechanism involving increased cyclic AMP levels resulting from loss of responsiveness to endogenous inhibitors such as adenosine.
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PMID:Promotion of lipolysis in rat adipocytes by pertussis toxin: reversal of endogenous inhibition. 619 60

Capillaries isolated by collagenase digestion of hamster epididymal fat pads were used to examine the properties of endothelial adenylate cyclase and cyclic nucleotide phosphodiesterase. Adenylate cyclase activity in capillary homogenates was increased by 10 microM GTP or 100 microM isoproterenol. Lower concentrations of the catecholamine and 5.7 microM prostaglandin E1 did not stimulate endothelial adenylate cyclase activity unless GTP was included in the assay system. The effects of isoproterenol on capillary adenylate cyclase activity were blocked by propranolol, but were not affected by phentolamine. Phosphodiesterase activity in endothelial homogenates showed anomalous kinetic behavior with either cyclic AMP or cyclic GMP as the enzyme substrate. At substrate concentrations below 1 microM, capillary phosphodiesterase activity hydrolyzed cyclic GMP 2-6 times faster than cyclic AMP. However, at high substrate levels, e.g., 100 microM, cyclic AMP and cyclic GMP were degraded at similar rates. Hydrolysis of 1 microM cyclic AMP by capillary homogenates was stimulated by 0.1 and 1 microM cyclic GMP. Caffeine, 1-methyl-3-isobutylxanthine, papaverine and dipyridamole SQ 20009 were effective inhibitors of capillary phosphodiesterase activity. In contrast, imidazole enhanced the activity of the enzyme. The presence of adenylate cyclase and phosphodiesterase activities in hamster isolated capillaries is consistent with a role for cyclic AMP in the regulation of endothelial function. Moreover, the experiments described here indicate that hamster isolated capillaries are useful model systems for studying the metabolism of vascular endothelium.
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PMID:Properties of adenylate cyclase and cyclic nucleotide phosphodiesterase in hamster isolated capillary preparations. 624 1

Most current etiologic concepts of Graves' disease postulate that this is an autoimmune disorder. A humoral factor, such as thyroid stimulating immunoglobulin, may be the mediator. On the other hand, it has also been suggested that abnormalities in the thyroid gland itself might be responsible for hyperfunction of the gland in Graves' disease. The true etiology of Graves' disease is still unknown. Similarly, the pathogenesis of the ophthalmic changes of Graves' disease is obscure, but immune mechanisms figure prominently in current hypotheses of the pathogenesis. It has been suggested that human adipose cell membranes have TSH receptors and that antibodies reacting with the receptors may stimulate fat cells. In this study, we have evaluated TSH receptor and adenylate cyclase of Graves' thyroid glands. Furthermore, we have investigated those of retro-orbital and the other adipose tissues in the guinea pig and in man. Human thyroid tissues were obtained at surgery and immediately minced homogenized with a loose-fitting Dounce homogenizer. A part of 10,000 g pellet of the homogenate was used for adenylate cyclase assay. The rest of the pellet was further purified by a discontinuous sucrose gradient ultracentrifugation, and the plasma membrane fraction was used for the receptor assay. The 125I-TSH binding to the fraction was measured, and the affinity constant (Ka) and capacity (Ro) were obtained from Scatchard plots using Rosenthal's method of analysis. Normal thyroid tissue contained high affinity (Ka = 2.4 x 10(10) M-1; Ro = 0.9 pmole/mg protein) and low affinity (Ka = 1.9 x 10(8) M-1; Ro = 386 pmole/mg protein) receptors. The two orders of TSH receptor were also found in Graves' thyroid tissue. The affinity constant and capacity of high affinity receptors were identical with those of normal thyroids, but the affinity constant of low affinity receptors was lower in Graves' thyroid (P less than 0.05). The basal adenylate cyclase activity in normal thyroid tissues was 0.35 nmole/10 min/mg protein. The activity rose to 280% of basal with 166 mU/ml of TSH and 680% of basal with 10 mM of NaF. These values obtained in Graves' disease were not significantly different from the values of normal thyroids. It is concluded that thyroid hyperfunction in Graves' disease is probably not the result of an intrinsic abnormality of the TSH receptor-adenylate cyclase system. Human retro-orbital adipose tissue was obtained at surgery from patients of Graves' exophthalmos or malignant neoplasm of accessory sinus. Guinea pigs tissue was obtained from 250g male animals. We were unable to demonstrate high affinity TSH receptor in human retro-orbital fat, perirenal fat or guinea pig retro-orbital fat. In contrast, guinea pig epididymal fat membranes showed TSH receptor characteristics similar to guinea pig thyroid membranes. In human adipose tissue, TSH did not stimulate the adenylate cyclase activity, although NaF definitely stimulated the enzyme...
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PMID:[Studies on the thyrotropin receptor and adenylate cyclase activity in various thyroid diseases: I. The properties of TSH receptor and adenylate cyclase in Graves' thyroid and retro-orbital adipose tissues (author's transl)]. 624 86


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