Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.6.1.2 (guanylate cyclase)
 8,497 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Some properties of guanylate cyclase, which was solubilized from the rabbit heart washed particles by the treatment with Triton X-100, were investigated. The solubilized enzyme activity was stimulated by Mg2+ in the presence of low (subsaturating) Mn2+ (GTP is greater than Mn2+); under these conditions, Ga2+ was inhibitory. At subsaturating MnGTP and free Mn2+, the solubilized enzyme was markedly stimulated by MnGDP and MnATP; CaGTP on the other hand, was inhibitory. These results are consistent with the view that the particulate guanylate cyclase may exist in the cell as a metalloenzyme with tightly bound Mn2+ and that Mg2+ supports its catalysis while Ca2+ as well as nucleotides may exert regulatory effects on its activity.
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PMID:Interactions of divalent cations and nucleotides with solubilized cardiac guanylate cyclase. 1 29

Kinetic properties of guanylate cyclase present in the washed particles, plasma membranes, and the soluble cytoplasm of heart and skeletal muscle are described; properties of the enzyme solubilized by Triton X-100 treatment of the particles or membrane fractions are also reported. It is apparent from the data that the membrane-bound guanylate cyclase in the cell may be regulated by acetylcholine, may exist as a metallo-protein with bound Mn2+ (essential for activity), and that Mg2+ regulates, whereas Ca2+ and nucleotides (especially ATP) modulate, guanylate cyclase activity. The findings also suggest that guanylate cyclase, similar to adenylate cyclase and (Na+, K+)-ATPase, is mainly located in the plasma membranes of heart and skeletal muscle.
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PMID:Properties of membrane-bound and soluble guanylate cyclase of cardiac and skeletal muscle. 2 2

Guanylate cyclase (GTP pyrophosphate-lyse (cyclizing), EC 4.6.1.2.) of bovine retinal rod outer segments is almost completely particulate, i.e. associated with rod outer segment membranes. In contrast to particulate guanylate cyclase in other tissues, treatment of rod outer segments with Triton X-100 does not solublize the enzyme but inhibits it. Enzyme activity is dependent on the presence of divalent cation, especially Mn2+ with only poor activation by Mg2+ (10-fold lower) and no activation seen with other cation. Ezpression of maximal activity required Nm2+ and GTP in equimolar concentrations with an apparent Km of 8 . 10(-4) M and V of 10 nmol/min per mg protein. Excess of Mn2+ over that required for the formation of the Mn . GTP complex was inhibitory. Ca2+, Ba2+ and Co2+ inhibited enzyme activity when assayed with the Mn . GTP substrate complex. In the presence of a fixed concentration of 1mM Mn2+, the enzyme exhibited strong negative cooperative interactions with GTP, characterized by an intermediary plateau region in the substrate vs. enzyme activity curve, a curve of downward concavity in the double reciprocal plot and a Hill coefficient of 0.5. Nucleotides such as ITP, ATP and UTP at higher concentrations (1 mM) stimulates activity by 40%. NaN3 has no effect on the guanylate cyclase. It is thus possible that the guanylate cyclase may be regulated in vivo by both the metal : GTP substrate ratio and the free divalent cation concentration as well as by the ATP concentration and thus play an important but yet undefined role in the visual process.
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PMID:Characterization of guanylate cyclase of rod outer segments of the bovine retina. 2 9

The effects of a variety of agents on guanylate cyclase activity were tested in broken cell preparations of mammary glands from midpregnant mice. Of the agents tested, only phospholipase A, triton X-100, and an impure egg lysolecithin preparation enhanced the activity of guanylate cyclase in mammary gland homogenates; other agents, including sodium azide and phospholipase C, and purified egg lysolecithin had no effect. Phospholipase A increased the activity of guanylate cyclase in the 150,000 g pellet fractions of mammary gland homogenates, bud did not consistently enhance guanylate cyclase in the 150,000 g supernatant fractions. Phospholipase A did not appear to enhance guanylate cyclase activity by solublizing the enzyme from the 150,000 g pellet. Triton X-100, in contrast, appeared to act by solubilizing guanylate cyclase from the material present in the 150,000 g pellet. Triton X-100 increased by several fold guanylate cyclase activity in the tissue homogenates and the 150,000 g pellets, but did not consistently enhance enzyme activity in the 150,000 g supernatant. Triton X-100 had no effect on the apparent Km of guanylate cyclase.
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PMID:Effects of phospholipase A and triton x-100 on guanylate cyclase activity in mammary gland homogenates from mice. 2 72

1. Under optimal ionic conditions (4 mM-MnCl2) the specific activity of guanylate cyclase in fresh platelet lysates was about 10nmol of cyclic GMP formed/20 min per mg of protein at 30 degrees C. Activity was 15% of optimum with 10mM-MgCl2 and negligible with 4mM-CaCl2. Synergism between MnCl2 and MgCl2 or CaCl2 was observed when [MnCl2] less than or equal to [GPT]. 2. Lower than optimal specific activities were obtained in assays containing large volumes of platelet lysate, owing to the presence of inhibitory factors that could be removed by ultrafiltration. Adenine nucleotides accounted for less than 50% of the inhibitory activity. 3. Preincubation of lysate for 1 h at 30 degrees C increased the specific activity of platelet guanylate cyclase by about 2-fold. 4. Lubrol PX (1%, w/v) stimulated guanylate cyclase activity by 3--5-fold before preincubation and by about 2-fold after preincubation. Triton X-100 was much less effective. 5. Dithiothreitol inhibited the guanylate cyclase activity of untreated, preincubated and Lubrol PX-treated lysates and prevented activation by preincubation provided that it was added beforehand. 6. Oleate stimulated guanylate cyclase activity 3--4-fold and arachidonate 2--3-fold, whereas palmitate was almost inactive. Pretreatment of lysate with indomethacin did not inhibit this effect of arachidonate. Oleate and arachidonate caused marked stimulation of guanylate cyclase in preincubated lysate, but inhibited the enzyme in Lubrol PX-treated lysate. 7. NaN3 (10mM) increased guanylate cyclase activity by up to 7-fold; this effect was both time- and temperature-dependent. NaN3 did not further activate the enzyme in Lubrol PX-treated lysate. 8. The results indicated that preincubation, Lubrol PX, fatty acids and NaN3 activated platelet guanylate cyclase by different mechanisms. 9. Platelet particulate fractions contained no guanylate cyclase activity detectable in the presence or absence of Lubrol PX that could not be accounted for by contaminating soluble enzyme, suggesting that physiological aggregating agents may increase cyclic GMP in intact platelets through the effects of intermediary factors. The activated and inhibited states of the enzyme described in the present paper may be relevant to the actions of these factors.
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PMID:Factors affecting the activity of guanylate cyclase in lysates of human blood platelets. 2 7

The subcellular distributions of adenylate cyclase and guanylate cyclase were determined for the mature enterocyte from the rat duodenum. Brush-border and basolateral membranes were prepared from isolated cells by an analytical isolation procedure, and multiple linear regression analysis was used to obtain a quantitative estimate of the distribution of recovered cyclase activities between the brush borders and basolateral membranes. Adenylate cyclase was largely confined to the basolateral surface of the epithelium, whereas guanylate cyclase was found on the brush-border and basolateral membrane fractions in the ratio 2.4:1. There was no evidence for the presence of nucleotide cyclases in the cytosol. Guanylate cyclase in both the brush-border and basolateral membranes was stimulated by epinephrine, insulin, and Triton X-100, but not by carbachol. Adenylate cyclase was not influenced by epinephrine, but was markedly stimulated by NaF and vasoactive intestinal peptide. These results are discussed in relation to the effects of hormones on transport across the small intestine.
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PMID:Subcellular distribution of nucleotide cyclases in rat intestinal epithelium. 3 94

The properties of particulate guanylate cyclase (GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2) from purified rabbit skeletal muscle membrane fragments were studied. Four membrane fractions were prepared by sucrose gradient centrifugation and the fractions characterized by analysis of marker enzymes. Guanylate cyclase activity was highest in the fraction possessing enzymatic properties typical of sarcolemma, while fractions enriched with sarcoplasmic reticulum had lower activities. In the presence of suboptimal Mn2+ concentrations, Mg2+ stimulated particulate guanylate cyclase activity both before and after solubilization in 1% Triton X-100. Guanylate cyclase activity was biphasic in the presence of Ca2+. Increasing the Ca2+ concentration from 10(-8) to 10(-5) M decreased the specific activity. As the Ca2+ concentration was further increased to 5 . 10(-4) M enzyme activity again increased. After solubilization of the membranes in 1% Triton X-100, Ca2+ suppressed enzyme activity. Studies utilizing ionophore X537A indicated that the altered effect of Ca2+ upon the solubilized membranes was independent of asymmetric distribution of Ca2+ and Mg2+.
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PMID:Particulate guanylate cyclase of skeletal muscle: effects of Ca2+ and other divalent cations on enzyme activity. 3 38

Guanylate cyclase activity (GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2.), measured in purified rat liver plasma membranes, was markedly increased by treatment with various purified proteases. The effect was maximal with trypsin, alpha-chymotrypsin, papain, and thermolysin (6- to 8-fold increase with 5 to 20 microgram of protease/ml) and lower with subtilisin and elastase (3- to 4-fold increase). The activation was due to an increase in the maximal velocity of the cyclizing reaction. No modification was observed either in the apparent affinity for the substrate MnGTP or in the cooperative behavior of the enzyme kinetics which displayed Hill coefficients of 1.6 for both basal and activated states. The Triton X-100-dispersed guanylate cyclase remained sensitive to papain, which suggests that the action of proteases was not restricted to an indirect action upon the membranous environment of the guanylate cyclase. In contrast, the cytosolic soluble guanylate cyclase, assayed in the presence or absence of sodium azide, was absolutely insensitive to papain. Thus, proteolysis represents a previously undescribed mechanism for activating membranous guanylate cyclase systems, which might be of importance in the physiological regulation of this enzyme.
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PMID:Activation of rat liver guanylate cyclase by proteolysis. 3 29

Mn2+ and to some degree Fe2+, but not Mg+, Ca2+, ba2+, Sr2+, Co2+, Ni2+, La3+, or Fe3+ were able to serve as effective metal cofactors for sea urchin sperm guanylate cyclase. The apparent Michaelis constant for Mn2+ in the presence of 0.25 mM MnGTP was 0.23 mM. In the presence of a fixed free mn2+ concentration, variation in mngTP resulted in sigmoid velocity-substrate plots and in reciprocal plots that were concave upward. These positive cooperative patterns were observed at both pH 7.0 and 7.8 and in the presence or absence of Triton X-100. When Mn2+ and GTP were equimolar, Ca2+, Ba2+, Sr2+, and Mg2+ increased apparent guanylate cyclase activity. This increase in enzyme activity at least could be accounted for partially by an increase in free Mn2+ concentration caused by the complex formation of GTP with the added metals. However, even at relatively low GTP concentrations and with Mn2+ concentrations in excess of GTP, Ca2+, Sr2+, and Ba2+ significantly increased guanosine 3':5'-monophosphate production. As the total GTP concentration was increased, the degree of stimulation in the presence of Ca2+ decreased, despite maintenance of a fixed total concentration of Ca2+ and a fixed free concentration of Mn2+, suggesting that the concentration of CaGTP and MnGTP were determining factors in the observed response. The concave upward reciprocal plots of velocity against MnGTP concentration were changed to linear plots in the presence of CaGTP or SrGTP. These results suggest that sea urchin sperm guanylate cyclase contains multiple nucleotide binding sites and that stimulation of guanosine 3':5'-monophosphate synthesis by Ca2+, Sr2+, and perhaps other metals may reflect interaction of a metal-GTP complex with enzyme as either an effector or a substrate.
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PMID:Effects of cations on guanylate cyclase of sea urchin sperm. 23 26

1. The localisation and some of the properties of rabbit kidney cortex guanylate cyclase (GTP pyrophosphatase lyase (cyclizing) EC 4.6.1.2) have been studied. Upon fractionation of dissociated renal cortex, guanylate cyclase activity was preferentially enriched in fractions of pure glomeruli, where its specific activity was 44.5 times that measured in tubular fragments. Most, if not all, of the glomerular activity was found to be firmly membrane-bound, whereas the guanylate cyclase activity of the tubules was mainly soluble. Therefore, particulate guanylate cyclase activity could serve as marker enzyme for kidney glomeruli. 2. All hormones or hormone-like agents tested were without effect on kidney guanylate cyclase activity. Triton X-100 stimulated both glomerular and tubular activity. 3. Considering the high cyclic GMP forming capacity of kidney glomeruli, part of the cyclic GMP found in urine might be synthetized locally in these structures.
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PMID:Renal cortex guanylate cyclase. Preferential enrichment in glomerular membranes. 23 9


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