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:3.6.1.25 (triphosphatase)
1,529 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A comparison of kinetic parameters (Km(app) and V) of hydrolysis by heavy meromyosin of natural (ATP and ITP) and modified nucleoside triphosphates showed that in the K+, EDTA-ATPase conformation the enzyme exhibited a higher selectivity towards the structure of the substrate nucleoside moiety than in the case of the Ca2+-stimulated nucleoside triphosphatase activity. In the presence of Ca2+, all the N1- and N6-substituted analogs of ATP as well as ITP, etheno-ATP and the dialdehyde derivative of ATP were hydrolyzed at a high rate irrespective of their markedly decreased affinity for heavy meromyosin. In the presence of K+, EDTA the ATPase activity showed a tendency for a total decrease of the analog affinity for nucleoside triphosphates, i.e., the impossibility of tight binding of the substrate phosphate residues to the protein in the absence of bivalent cations, which was concomitant with an increase in the hydrolysis rate. However, it was found that only in N1-substituted analogs any appreciable changes in the substrate properties were absent. All the other nucleoside triphosphates tested (N6-carboxy-methoxy-ATP, N6-(N'-acetylaminoethoxy)-ATP, etheno-ATP, ITP and the dialdehyde derivative of ATP having a rupture in the ribose ring) lost their ability to be hydrolyzed by heavy meromyosin. The experimental results as well as the literature data are suggestive of differences in the spatial structure of the active center in two different myosin conformations associated with a high catalytic activity, i.e., K+, EDTA-ATPase and Ca2+-ATPase.
...
PMID:[Increased substrate selectivity during transition from Ca2+-activated to K+,EDTA-activated nucleoside triphosphatase activity of heavy meromyosin]. 296 18

The incision of damaged DNA by the Escherichia coli UvrABC endonuclease requires ATP hydrolysis. Although the deduced sequence of the UvrB protein suggests a putative ATP binding site, no nucleoside triphosphatase activity is demonstrable with the purified UvrB protein. The UvrB protein is specifically proteolyzed in E. coli cell extracts to yield a 70 kD fragment, referred to as UvrB*, which has been purified and is shown to possess a single-strand DNA dependent ATPase activity. Substrate specificity and kinetic analyses of UvrB* catalyzed nucleotide hydrolysis indicate that the stimulation in DNA dependent ATPase activity following formation of the UvrAB complex results from the activation of the normally sequestered UvrB associated ATPase. Using nucleotide analogues, it can be shown that this activity is essential to the DNA incision reaction carried out by the UvrABC complex.
...
PMID:Involvement of a cryptic ATPase activity of UvrB and its proteolysis product, UvrB* in DNA repair. 1661 84

In the presence of Mg2+ the ecto-(nucleoside diphosphatase) on intact vascular endothelial or smooth muscle cells in culture selectively catabolizes the PS diastereoisomer of adenosine 5'-[alpha-thio]diphosphate, (PS)-ADP [alpha S], and the ecto-(nucleoside triphosphatase) selectively catabolizes the PS isomer of adenosine 5'-[beta-thio]triphosphate, (PR)-ATP[beta S], but exhibits no selectivity towards ATP[alpha S] isomers. In the presence of Cd2+ selectivity to ADP[alpha S] and to ATP[beta S] isomers is reversed; in the presence of Co2+, selectivity is lost. We conclude that each enzyme preferentially recognises the lambda (screw-sense) bidentate Mg(II)-nucleotide complex at its active site.
...
PMID:Investigation of the preferred Mg(II)-adenine-nucleotide complex at the active site of ectonucleotidases in intact vascular cells using phosphorothioate analogues of ADP and ATP. 299 64

Intact synaptosomes isolated from the electric organ of the electric ray Torpedo marmorata contain, at their surface, enzyme activities for the hydrolysis of externally applied nucleoside phosphates. The diazonium salt of sulfanilic acid, as a low-molecular-weight, slowly permeating, covalent inhibitory agent, selectively blocks these enzyme activities and leaves intracellular lactate dehydrogenase intact. The ectoenzymes comprise both a nucleoside triphosphate and diphosphate phosphohydrolase, as well as a 5'-nucleotidase. Activity of nonspecific ectophosphatases is absent. The nucleoside triphosphatase hydrolyzes almost equally well ATP, GTP, CTP, UTP, and ITP and is activated to a similar degree by Mg2+ or Ca2+. It has a high affinity for ATP (Km for ATP in the presence of Mg2+, 75 microM; in the presence of Ca2+, 66 microM). Maximal rates in the presence of Mg2+ and Ca2+ were very similar (34.8 and 32.5 nmol of Pi/min/mg of synaptosomal protein, respectively). Either Mg-ATP or Ca-ATP can act as a true substrate. ADP inhibits hydrolysis of ATP, but AMP is without effect. The nucleoside triphosphatase is not inhibited significantly by a number of inhibitors of mitochondrial Mg2+-ATPase or of Ca2+ + Mg2+-ATPases. It is, however, considerably inhibited by filipin and quercitin. The capacity of intact synaptosomes to hydrolyze also extracellular ADP, GDP, AMP, GMP, and IMP suggests that the nucleoside triphosphatase is part of an enzyme chain that causes complete hydrolysis of the respective nucleoside triphosphate to the nucleoside. We conclude that the cholinergic nerve terminals of the Torpedo electric organ can hydrolyze ATP released on coexocytosis with acetylcholine via an ectonucleoside triphosphatase activity that is different from known endogenous nerve terminal ATPases. The final product of the hydrolysis, adenosine, can then be salvaged by the nerve terminal for resynthesis of ATP. Other possible physiological functions of the ectonucleotidases are discussed.
...
PMID:Ectonucleotidase activities associated with cholinergic synaptosomes isolated from Torpedo electric organ. 301 88

A membrane-bound nonspecific triphosphatase of E. coli was solubilized and purified to a homogeneous SDS-acrylamide gel electrophoresis band. It was found to be a single polypeptide of 16 kDa requiring no Mg2+, with an optimal pH at 6.5. The substrate specificity was broad and a nonspecific Mg2+-independent ribonucleoside-triphosphatase (NTPase) activity was expressed together with thiamin-triphosphatase activity. The molecular size and characteristics were clearly different from the known NTPase (EC 3.6.1.15). Using the purified thiamin-triphosphatase II, ATP:thiamin-diphosphate phosphoryl transferase (EC 2.7.4.15) activity was demonstrated with an optimal pH of approx. 5.3. Considering its kinetic parameters and other characteristics, however, the thiamin triphosphate synthesizing activity was not thought to take part in cellular thiamin triphosphate synthesis. The possibility that thiamin-triphosphatase II plays a part in the hydrolysis of thiamin triphosphate to control its cellular level is suggested.
...
PMID:Nucleoside-triphosphatase and hydrolysis of thiamin triphosphate in Escherichia coli. 302 93

Escherichia coli helicase II has been purified to near homogeneity from cells harboring a multicopy plasmid containing the structural gene for helicase II, uvrD. In this paper a detailed description of the single-stranded DNA-dependent nucleoside 5'-triphosphatase and helicase reactions catalyzed by helicase II is presented. The results of this study suggest that nucleoside 5'-triphosphate hydrolysis provides the energy required for translocation of the enzyme along single-stranded DNA. Measurements of the rate of ATP hydrolysis using a variety of single-stranded DNAs of known structure and length suggest a processive translocation mechanism for helicase II. Single-stranded DNA coated with either Escherichia coli single-stranded DNA binding protein (SSB) or bacteriophage T4 gene 32 protein fails to support helicase II ATPase activity. Moreover, helicase II is apparently unable to displace a molecule of bound SSB protein from single-stranded DNA when it is encountered in the process of translocation along a single-stranded DNA effector. The helicase reaction has been characterized using an in vitro strand displacement helicase assay. The helicase reaction requires concomitant nucleoside 5'-triphosphatase hydrolysis that is satisfied by the hydrolysis of either rATP or dATP. As the length of duplex DNA present in the partial duplex helicase substrate is increased from 71 base pairs to 343 base pairs, the fraction of duplex DNA molecules that are unwound by helicase II decreases in the absence of any accessory proteins. However, the total number of base pairs of duplex DNA unwound depends primarily on the amount of enzyme added to the helicase reaction and not on the length of the duplex DNA present in the partial duplex DNA substrate. These data suggest the number of base pairs of duplex DNA unwound is directly proportional with the concentration of helicase II in the reaction mixture. In addition, the rate of the unwinding reaction is independent of the length of the duplex DNA available for unwinding. Helicase II has been shown to dissociate from single-stranded DNA molecules infrequently acting as an ATPase. However, the enzyme dissociates from partial duplex helicase substrates more frequently. This suggests a more distributive reaction mechanism on duplex DNA than was observed on single-stranded DNA substrates. The fraction of 343-base pair partial duplex DNA molecules unwound by helicase II can be increased by the addition of appropriate concentrations of E. coli SSB to the reaction. This suggests that helicase II and SSB may act in a concerted reaction to unwind duplex DNA.
...
PMID:DNA helicase II of Escherichia coli. Characterization of the single-stranded DNA-dependent NTPase and helicase activities. 302 63

The dnaB protein of Escherichia coli, a multifunctional DNA-dependent ribonucleotide triphosphatase and dATPase, cross-links to ATP on ultraviolet irradiation under conditions that support rNTPase and dATPase activities of dnaB protein. The covalent cross-linking to ATP is specifically inhibited by ribonucleotides and dATP. Tryptic peptide mapping demonstrates that ATP cross-links to only the 33-kDa tryptic fragment (Fragment II) of dnaB protein. The presence of single-stranded DNA alters the covalent labeling of dnaB protein by ATP, suggesting a possible role of DNA on the mode of nucleotide binding by dnaB protein. Present studies demonstrate that the dnaC gene product binds ribonucleotides independent of dnaB protein. On dnaB-dnaC protein complex formation, covalent incorporation of ATP to dnaB protein decreases approximately 70% with a concomitant increase of ATP incorporation to dnaC protein by approximately 3-fold. The mechanism of this phenomenon has been analyzed in detail by titrating dnaB protein with increasing amounts of dnaC protein. The binding of dnaC protein to dnaB protein appears to be a noncooperative process. The lambda P protein, which interacts with dnaB protein in the bacteriophage lambda DNA replication, does not bind ATP in the presence or absence of dnaB protein. However, lambda P protein enhances the covalent incorporation of ATP to dnaB protein approximately 4-fold, suggesting a direct physical interaction between lambda P and dnaB proteins with a probable change in the modes of nucleotide binding to dnaB protein. The lambda P protein likely forms a lambda P-dnaB-ATP dead-end ternary complex. The implications of these results in the E. coli and bacteriophage lambda chromosomal DNA replication are discussed.
...
PMID:Regulation of dnaB function in DNA replication in Escherichia coli by dnaC and lambda P gene products. 303 7

The main electric organ of Electrophorus electricus is particularly rich in thiamine triphosphate, which represents 87% of the total thiamine content in this tissue. The thiamine pyrophosphate concentration, however, is very low in the eel electric organ and skeletal muscle as compared with other eel or rat tissues. Furthermore, electroplax membranes contain a whole set of enzymes responsible for the dephosphorylation of thiamine tri-, pyro- and monophosphate. Thiamine triphosphatase has a pH optimum of 6.8 and is dependent on Mg2+. The real substrate of the enzyme is probably a 1:1 complex of Mg2+ and thiamine triphosphate. Thiamine pyrophosphatase is activated by Ca2+. The apparent Km for thiamine triphosphate and Vmax are found to be, respectively, 1.76 mM and 5.95 nmol/mg of protein/min. Thiamine triphosphatase activity is inhibited at physiological K+ concentrations (up to 90 mM) and increasing Na+ concentrations (50% inhibition at 300 mM). ZnCl2 (10 mM) inhibits 90% of the enzyme activity. ATP and ITP are also strongly inhibitory. No significant effect of neurotoxins is seen. Membrane-associated thiamine triphosphatase is affected differently by proteolytic enzymes and is partially inactivated by pretreatment with phospholipase C and neuraminidase. The physiological significance of thiamine triphosphatase is discussed in relation to a specific role of thiamine in the nervous system.
...
PMID:Thiamine triphosphate and membrane-associated thiamine phosphatases in the electric organ of Electrophorus electricus. 303 30

The cooperativity of the single-stranded DNA dependent nucleoside triphosphatase activity of the recA protein was investigated by examining the influence of a good substrate (ATP) on the hydrolysis of a poor substrate (GTP). At pH 7.5 and 37 degrees C, both ATP and GTP are hydrolyzed with a turnover number of 17.5 min-1. The S0.5 for GTP (750 microM), however, is nearly 20-fold higher than the S0.5 for ATP (45 microM). Low concentrations of ATP activate the GTPase activity of the recA protein by lowering the S0.5 for GTP; in the presence of 50 microM ATP, the S0.5 for GTP is reduced from 750 microM to 200 microM. Concentrations of ATP greater than 50 microM result in competitive inhibition of the ATP-activated GTPase activity. Although GTP is a substrate for hydrolysis, it will not substitute for ATP as a high-energy cofactor in the standard recA protein promoted three-strand exchange reaction. To account for these results, a minimal kinetic model is presented in which ATP binding induces specific conformational changes in the recA protein that do not occur with GTP binding.
...
PMID:ATP-stimulated hydrolysis of GTP by RecA protein: kinetic consequences of cooperative RecA protein-ATP interactions. 328 16

In the present study, the structural and functional role of smooth endoplasmic reticulum was investigated in bullfrog olfactory axon terminals. Structural evidence obtained from this study indicated that this vesiculotubular organelle becomes a more elaborate network of anastomosing tubules near the nerve terminal, located in the olfactory lobe of frog brain. Further structural evidence suggested that membranes of the smooth endoplasmic reticulum pinch off to give rise to some electron-lucent vesicles of approximately 50 nm diameter (microvesicles). Ultrastructural cytochemistry was employed in the present study to demonstrate that olfactory axon terminal smooth endoplasmic reticulum actively sequesters Ca2+. However, a variable amount of electron-dense product (calcium oxalate) was associated with microvesicles located at a distance from the synapse, in contrast to those clustered near the synapse which usually did not contain this reaction product. Results from Ca2+-Mg2+-adenosine-5'-triphosphatase (ATPase) cytochemistry showed a similar pattern of distribution, with smooth endoplasmic reticulum being densely labeled with ATPase reaction product (lead phosphate), but aggregated microvesicles in the nerve terminal generally lacking this electron-dense product. Therefore, it is concluded that olfactory axonal smooth endoplasmic reticulum plays a role in the regulation of intraneuronal Ca2+ levels, and that the Ca2+-sequestering activity of this membranous organelle is dependent upon enzymatic hydrolysis of ATP. Conversely, the microvesicles, particularly those accumulated near the synapse, lack this Ca2+-pumping capacity. Thus, if some of the microvesicles originate from smooth endoplasmic reticulum membranes which are capable of pumping Ca2+, but these vesicles themselves lack this capacity, one can postulate that the Ca2+ pumps are either removed from the newly formed microvesicle membranes or are somehow incapacitated in situ in the membrane.
...
PMID:Distribution and calcium-sequestering ability of smooth endoplasmic reticulum in olfactory axon terminals of frog brain. 350 Apr 27


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

---