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PubMed1983

Intracellular pH determination by a 31P-NMR technique. The second dissociation constant of phosphoric acid in a biological system.

To evaluate the accuracy of pH determination by 31P-NMR, factors which influence the pK value of phosphate were appraised on the basis of the titration of 1 mM phosphate buffer solution. When the method is used for the determination of cytoplasmic pH, ionic strength is the major factor causing shifts of apparent pK (pK') value, and the magnitude of the shift can be predicted from the ionic strength calculated by means of the Debye-Hückel equation. Ions (Na+, K+, Mg2+, and Ca2+) and salivary protein affected the pK' value by 0.1 to 0.3 units in solution with a given ionic strength depending on the species of ion. The form of the titration curve varied with temperature. Based on these results, the value of 6.75 was obtained with the uncertainty of 0.12 for the intracellular pK' of frog muscle at 24 degrees C.

Animals↗
PubMed1982

Inhibitory action of cyclic guanosine 5'-phosphoric acid (GMP) on oocyte maturation: dependence on an intact cumulus.

Oocyte cumulus complexes (OCC) were isolated from antral follicles of proestrous hamsters prior to the luteinizing hormone (LH)/follicle-stimulating hormone (FSH) surge and then incubated from 4 to 24 h at 37 degrees C. Under these conditions approximately 89% of the oocytes exhibited metaphase plates (11% were in the dictyate stage) and addition of LH (200 ng/ml ovine NIH-LH-S20) did not significantly alter the percentage of oocyte maturation. Approximately 50% of the OCC incubated for 24 h with 6 mM 8-bromo-cyclic quanine 3':5' monophosphate (8-Br-cGMP) were prevented from maturing beyond the dictyate stage. OCC incubated with 6 mM 8-bromo-cyclic adenosine 3':5' monophosphate (8-Br-cAMP) were also prevented from maturing (59.5% 8-Br-cAMP) in vitro. LH (200 ng/ml) was able to overcome the 8-Br-cAMP-induced inhibition of oocyte maturation in OCC. It also produced a decrease in 8-Br-cGMP mediated inhibition which was more pronounced when the dosage of LH was increased to 10 microgram/ml. 8-Br-cGMP prevented oocyte maturation in a dose and time dependent manner. Only 8-Br-cAMP prevented maturation (approximately 60% inhibition) of denuded oocytes in vitro. Denuded oocytes incubated with and without 8-Br-cGMP exhibited no inhibited of maturation. These results indicate that 8-Br-cGMP may exert its inhibitory effects through the cumulus cells. On the other hand, cAMP appears to directly inhibit oocyte maturation.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed2006

Dissociative electron attachment to phosphoric acid esters: the direct mechanism for single strand breaks in DNA.

We use dibutyl phosphate to simulate the behavior of the phosphate group in DNA towards the attack of low energy electrons. We find that the compound undergoes effective dissociative electron attachment within a low energy resonant feature at 1 eV and a further resonance peaking at 8 eV. The dissociative electron attachment (DEA) reactions are associated with the direct cleavage of the C-O and the P-O bond but also the excision of the PO-, PO3-, H2PO3- units. For the phosphate group coupled in the DNA network these reactions represent single strand breaks. We hence propose that the most direct mechanism of single strand breaks occurring in DNA at subexcitation energies (< 4 eV) is due to DEA directly to the phosphate group.

Computer Simulation↗
PubMed2006

Chemical interaction of phosphoric acid ester with hydroxyapatite.

Among functional monomers used in contemporary dental adhesives, 10-methacryloyloxydecyl dihydrogen phosphate (MDP) has been found to interact chemically with hydroxyapatite (HAp) most intensively and stably. This effect was thought to be the basis of the superior bonding effectiveness of MDP-based self-etch adhesives to enamel/dentin. To elucidate fully the chemical interaction and reactivity of MDP with HAp, we used (31)P CP-MAS NMR spectroscopy and powder x-ray diffraction. In an aqueous ethanol solution, Ca ions were leached from HAp to form, at short term, a MDP-calcium salt (CaMHP(2)) layered structure on the HAp surface. When MDP was allowed to interact for longer time (< 24 hrs), CaHPO(4).2H(2)O precipitated on top of this MDP-calcium salt layered structure. In conclusion, the intense chemical interaction of MDP with HAp must be ascribed to superficial dissolution of HAp induced by the MDP adsorption and subsequent deposition of MDP-calcium salt with a solubility lower than that of CaHPO(4).2H(2)O.

Adsorption↗
PubMedDate not supplied

[Determination of total and inorganic phosphorus in the presence of organic phosphoric acid esters and proteins].

Total phosphorus was estimated after mineralization of a sample, containing organic phosphoesters and proteins; a method is based on the formation of phosphomolybdenovanadium complex at acid pH. The analyses for inorganic phosphorus were carried our together with estimation if some labile phosphoesters (glucose-I-phosphate, ADP, ATP), which was possible due to low acidity of the medium (0.24 N HC1O4), small concentrations of reagents (3.2 mg/ml of molybdate, 0.08 mg/ml vanadate), addition of sodium citrate to neutralize the excess of molybdenovanadium acid and extraction of the colored complex with butyl or isobutyl alcohol. Optical density was measured at two wave lengths (340 nm and 390 nm) which enabled to estimate from 0.5 to 80 microng of phosphrorus in a sample.

Densitometry↗