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At least 19 recordsLinked to original sources
PubMed1973

Regulation of Succinate Dehydrogenase in Higher Plants: II. Activation by Substrates, Reduced Coenzyme Q, Nucleotides, and Anions.

The effect of various agents on the activation of succinate dehydrogenase in cauliflower (Brassica oleracea) and mung bean (Phaseolus aureus) mitochondria and in sonicated particles has been investigated. Reduced coenzyme Q(10), inosine diphosphate, inosine triphosphate, acid pH, and anions activate the enzyme in mitochondria from higher plants in the same manner as in mammalian preparations. Significant differences have been detected in the behavior of plant and animal preparations in the effects of ATP, ADP, NADH, NAD-linked substrates, and of 2, 4-dinitrophenol on the state of activation of the dehydrogenase. In mammalian mitochondria ATP activates, whereas ADP does not, and the ATP effect is shown only in intact mitochondria. In mung bean and cauliflower mitochondria, both ATP and ADP activate and the effect is also shown in sonicated and frozen-thawed preparations. In sonicated mung bean mitochondria NADH causes complete activation, as in mammalian submitochondrial particles, but in sonicated cauliflower mitochondria activation by NADH is incomplete, as is also true of intact, anaerobic cauliflower mitochondria. Moreover, neither NAD-linked substrates nor a combination of these with NADH can fully activate the enzyme in cauliflower mitochondria. In contrast to mammalian mitochondria, succinate dehydrogenase is not deactivated in cauliflower or mung beam mitochondria under the oxidized conditions brought about by uncoupling of oxidative phosphorylation by 2,4-dinitrophenol.

Journal Article↗
PubMed1991

On the mechanism of nucleotide diphosphate activation of the ATP-sensitive K+ channel in ventricular cell of guinea-pig.

1. Effects of intracellular nucleotide diphosphates (NDPs) on the ATP-sensitive K+ channel (K+ATP channel) were examined in ventricular cells of guinea-pig heart, using the inside-out patch clamp technique. On formation of inside-out patches in the ATP-free internal solution, the K+ATP channel appeared and then ran down spontaneously. This run-down of the K+ATP channel activity was probably due to dephosphorylation. 2. Millimolar concentrations of various NDPs, e.g. UDP (uridine diphosphate), IDP (inosine diphosphate), CDP (cytidine diphosphate) and GDP (guanosine diphosphate), applied to the internal side of the patch membrane, induced openings of the K+ATP channel after run-down, i.e. in the dephosphorylated state. ADP opened the channel weakly at low concentrations (100 microM) but inhibited it at higher concentrations (1-10 mM). 3. NDP-induced openings of the channel were Mg2+ dependent and inhibited by ATP (100 microM) and glibenclamide (1 microM). None of nucleosides, nucleotide monophosphates nor nucleotide triphosphates induced openings of the channel. Thus, the K+ATP channel may have a Mg(2+)-dependent NDP-binding site, which induces openings of the dephosphorylated channel in ATP-free solution, in addition to the Mg(2+)-independent ATP-binding inactivation site and phosphorylation site. 4. In inside-out patches, pinacidil (a K+ATP channel opener) activated the K+ATP channel in the phosphorylated state but not in the dephosphorylated state. In the presence of NDPs (UDP, IDP, CDP, GDP), however, pinacidil (30 microM) enhanced openings of the dephosphorylated K+ATP channel prominently. 5. From the above results, we concluded that NDP-binding to the specific site has similar effects to channel phosphorylation, i.e. it keeps the K+ATP channel in an operative state in ATP-free solution and enhances the pinacidil-induced channel openings.

Adenosine Diphosphate↗
PubMed1991

Differentiation between Several Types of Phosphohydrolases in Light Microsomes of Corn Roots.

The phosphohydrolase activity of a light microsomal fraction isolated from corn roots (Zea mays L. cv LG 55) was investigated. The fraction, which appears to be enriched in endoplasmic reticulum and Golgi membranes, has ATPase and pyrophosphatase activities that hydrolyze ATP and pyrophosphate at an optimum pH of 7.0, with K(m) values of about 160 and 240 micromolar and with V(max) values of about 200 and 50 nanomoles substrate hydrolyzed per milligram protein per minute, respectively. These enzymes differ in their sensitivity to anions and inhibitors. The ATPase is stimulated by sulfate anions, whereas pyrophosphatase is inhibited by molybdate. Furthermore, the simultaneous addition of ATP and pyrophosphate to the reaction medium increases phosphohydrolysis, suggesting that separate enzymes are operating in the membranes. We also observed that pyrophosphate competitively inhibits the ATPase, whereas ATP has no significant effect on the pyrophosphatase. On the other hand, we observed a detergent-stimulated, molybdate-insensitive inosine diphosphatase activity which, in the native state, hydrolyzes inosine diphosphate with a K(m) of about 700 micromolar and a V(max) of about 450 nanomoles inosine diphosphate hydrolyzed per milligram protein per minute. In the solubilized form, the enzyme appears to be fully active, exhibiting lower K(m) values to hydrolyze inosine diphosphate. Furthermore, we found that native inosine diphosphatase is inhibited either by ATP or pyrophosphate, whereas inosine diphosphate inhibits the ATPase, but has no significant effect on the pyrophosphatase. It appears that inosine diphosphate is a positive modulator of the inosine diphosphatase, whereas ATP and pyrophosphate act as negative modulators of this enzyme.

Journal Article↗
PubMed1984

Enzyme studies on TPPase-reactive cytoplasmic structures observed in early meiotic prophase I of the hamster oocyte.

Ovaries of immature and adult hamsters were incubated in medium containing thiamine pyrophosphate (TPP) to determine the age at which TPPase-reactive cytoplasmic structures first appear in the germ cells, and at what age the structures cease to be present. The structures were found only in oocytes from animals 8-15 days of age. They occur in predictyate germ cells in polyovular follicles and in very early dictyate oocytes in unilaminar follicles. The TPPase-reactive structures were never observed in atretic oocytes, in unilaminar follicles of adult animals, nor in multilaminar follicles of animals at any age. Ovaries of 8-12-day-old animals and adults were then incubated in media in which one of the following substrates was substituted for TPP: uridine diphosphate (UDP), inosine diphosphate (IDP), and adenosine monophosphate (AMP). Half of the samples in each experiment were incubated in medium containing the inhibitor L-p-bromotetramisole. beta-Glycerophosphate was used in control incubations, or the substrate was omitted entirely. The cytoplasmic structures were found to be reactive after incubation in UDP-containing media, but not after incubation in media containing AMP. With IDP as substrate, reactions were atypical and confined to peripheral regions of the cytoplasm. Other sites of enzyme activity after incubation with the various substrates (cell membranes, zona pellucida, endoplasmic reticulum and Golgi apparatus) are also described and discussed.

Aging↗
PubMed1984

Unusual C3 and C4 metabolism in the chemoautotroph Alcaligenes eutrophus.

Phosphoenolpyruvate (PEP) carboxykinase was identified to be the only C3-carboxylating enzyme in Alcaligenes eutrophus. The enzyme requires GDP or inosine diphosphate (GTP or inosine triphosphate) for activity. Pyruvate- and other PEP-dependent CO2-fixing enzyme activities were not detected, regardless of whether the cells were grown autotrophically or heterotrophically. It is suggested that two pathways are present in the organism for the formation of PEP from C4 dicarboxylic acids. Besides decarboxylation of oxaloacetate by PEP carboxykinase, the consecutive action of NADP+-malic enzyme and PEP synthetase can also accomplish this synthesis. An oxaloacetate decarboxylase activity observed in the cell extracts may also contribute to the latter route. The properties of a mutant deficient in PEP synthetase supported the biochemical data. This mutant was unable to grow on pyruvate or lactate and grew slower than the wild type on direct or indirect metabolites of the tricarboxylic acid cycle such as succinate, glutamate, or acetate. Growth on fructose and autotrophic growth were not affected by the enzyme defect. The findings suggest that, depending on the growth substrate utilized, PEP carboxykinase can serve a dual physiological function in A. eutrophus, an anaplerotic function in oxaloacetate synthesis from PEP, or a gluconeogenic function in PEP synthesis from oxaloacetate.

Alcaligenes↗
PubMed1977

Nucleoside diphosphatase in the onion root tip. II. The effect of inhibitors on isoenzymes.

An electrophoretic study was performed to determine the number of isoenzymes of nucleoside diphosphatase in onion root extract. Five bands exhibiting nucleoside diphosphatase activity were detected when gels were incubated with inosine diphosphate, uridine diphosphate, guanosine diphosphate or cytidine diphosphate as substrates. These consisted of a single fast migrating band (band one), a group of three intermediate migrating bands (bands two, three and four) and a single slow migrating band (band five). Gels incubated with adenosine diphosphate, thiamine pyrophosphate, inosine monophosphate, guanosine monophosphate and cytidine monophosphate showed only two bands (bands one and five). Inhibitor studies showed that sodium fluoride inhibited bands one and five but not bands two, three and four. Conversely, 1% (v/v) glutaraldehyde inhibited bands two, three and four but did not inhibit bands one and five. These results suggest that two separate groups of onion nucleoside diphosphatase isoenzymes occur which have different substrate specificities and are selected against by certain inhibitors.

Electrophoresis, Polyacrylamide Gel↗
PubMed1988

Trichomonas vaginalis: characterization of its glutamate dehydrogenase.

An NADP-linked glutamate dehydrogenase (EC 1.4.1.4) was found in the soluble fraction of Trichomonas vaginalis. Its molecular weight was about 230,000 (gel filtration). The enzyme, partially purified by diafiltration and hydroxyapatite column chromatography, was heat stable (1 hr at 57 C). It catalyzed both the amination of alpha-ketoglutarate (mean Km 0.6 mM) and the deamination of glutamate (mean Km 1.2 mM) The optimum pH of the amination reaction was 6.7, and that of the deamination reaction was 8. Glutamate was a competitive inhibitor of the amination reaction (mean Ki 5.6 mM) and alpha-ketoglutarate a partially competitive inhibitor of the deamination reaction (mean Ki 0.45 mM). Both guanosine and inosine diphosphates (1 mM) increased the Km alpha-ketoglutarate fivefold (mean Ki's 0.3 and 0.4 mM, respectively). Guanosine diphosphate reduced the Km glutamate 40%. Adenosine di- and triphosphate (1 mM) were ineffective. Because the amination reaction displayed substrate inhibition, guanosine and inosine diphosphates were potent natural inhibitors, and ammonia released by deamination reactions would tend to raise pH (amination operative at acid pH), we hypothesize that the deamination reaction may predominate in the living organism.

Amination↗
PubMed1981

Hypoxanthine nucleotides synthesis in fresh and stored human erythrocytes.

Human erythrocytes incubated in inosine-pyruvate-phosphate (IPP) medium are able to accumulate great amounts of inosine monophosphate (IMP) and inosine triphosphate (ITP). Accumulation of ITP is low in freshly drawn cells. It increases during blood storage in acid-citrate-dextrose solution. Addition of labelled inosine or hypoxanthine to the IPP medium allowed to show the synthesis of small amounts of inosine diphosphate and the appearance of radioactivity in the ATP fraction. Conditions of incubation and the pathways of hypoxanthine nucleotides synthesis are discussed.

Blood Preservation↗
PubMed1965

NUCLEOSIDE PHOSPHATASE ACTIVITIES IN RAT CARDIAC MUSCLE.

Localizations of aldehyde-resistant nucleoside phosphatase activities in frozen sections of rat cardiac muscle have been studied by electron microscopy. Activities are higher after fixation with formaldehyde than with glutaraldehyde. After incubation with adenosine triphosphate or inosine diphosphate at pH 7.2, reaction product is found in the "terminal cisternae" or "transverse sacs" of the sarcoplasmic reticulum, which, together with the "intermediary vesicles" (T system), constitute the "dyads" or "triads". Reaction product is also present at the membranes of micropinocytotic vacuoles which apparently form from the plasma membrane of capillary endothelial cells and from the sarcolemma. In certain regions of the intercalated discs, reaction product is found within the narrow spaces between sarcolemmas of adjacent cells and within micropinocytotic vacuoles that seem to form from the sarcolemma. With inosine diphosphate, reaction product is also found in other parts of the sarcoplasmic reticulum. After incubation with cytidine monophosphate at pH 5, reaction product is present in the transverse sacs of sarcoplasmic reticulum, in micropinocytotic vacuoles in capillary endothelium, and in lysosomes of muscle fibers and capillaries. The possible significance of the sarcoplasmic reticulum phosphatases is discussed in relation to the role the reticulum probably plays in moving calcium ions and thereby controlling contraction and relaxation of the muscle fiber.

Adenosine Triphosphate↗
PubMed1990

Clastogenic inosine nucleotide as components of the chromosome breakage factor in scleroderma patients.

In the present study, we attempted to identify the chemical nature of the clastogenic factor (CF) from patients with progressive systemic sclerosis (scleroderma). Computerized mass spectrometry of clastogenic fractions obtained by HPLC of plasma ultrafiltrates detected molecular peaks compatible with inosine triphosphate and inosine diphosphate (ITP and IDP). The concomitant detection of IDP, together with ITP, and the absence of these peaks in nonclastogenic fractions and corresponding control fractions are arguments in favor of a biological relevance of these observations. The most important confirmation came from the clastogenic effect of commercial ITP and IDP added to the culture medium of the test cultures. The induction of chromatid type damage by these substances in lymphocytes exposed in the G0 phase of their cell cycle and the prevention of this damage by superoxide dismutase are analogous to the observations with CF.

Cells, Cultured↗
PubMed1994

Hydrogen bond interactions of G proteins with the guanine ring moiety of guanine nucleotides.

We have utilized Raman difference spectroscopy to investigate hydrogen bonding interactions of the guanine moiety in guanine nucleotides with the binding site of two G proteins, EF-Tu (elongation factor Tu from Escherichia coli) and the c-Harvey ras protein, p21 (the gene product of the human c-H-ras proto-oncogene). Raman spectra of proteins complexed with GDP (guanosine 5' diphosphate), IDP (inosine 5' diphosphate), 6-thio-GDP, and 6-18O-GDP were measured, and the various difference spectra were determined. These were compared to the difference spectra obtained in solution, revealing vibrational features of the nucleotide that are altered upon binding. Specifically, we observed significant frequency shifts in the vibrational modes associated with the 6-keto and 2-amino positions of the guanine group of GDP and IDP that result from hydrogen bonding interactions between these groups and the two proteins. These shifts are interpreted as being proportional to the local energy of interaction (delta H) between the two groups and protein residues at the nucleotide binding site. Consistent with the tight binding between the nucleotides and the two proteins, the shifts indicate that the enthalpic interactions are stronger between these two polar groups and protein than with water. In general, the spectral shifts provide a rationale for the stronger binding of GDP and IDP with p21 compared to EF-Tu. Despite the structural similarity of the binding sites of EF-Tu and p21, the strengths of the observed hydrogen bonds at the 6-keto and 2-amino positions vary substantially, by up to a factor of 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗