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At least 1,243 records · Page 69Linked to original sources
PubMed1982

PhoE protein pore of the outer membrane of Escherichia coli K12 is a particularly efficient channel for organic and inorganic phosphate.

This study was undertaken to investigate the proposed in vivo pore function of PhoE protein, an Escherichia coli K12 outer membrane protein induced by growth under phosphate limitation and to compare it with those of the constitutive pore proteins OmpF and OmpC. Appropriate mutant strains were constructed containing only one of the proteins PhoE, OmpF or OmpC, or none of these proteins at all. By measuring rates of nutrient uptake at low solute concentrations, the proposed pore function of PhoE protein was confirmed as the presence of the protein facilitates the diffusion of Pi through the outer membrane, such as a pore protein deficient strain behaves as a Km mutant. Comparison of the rates of permeation of Pi, glycerol 3-phosphate and glucose 6-phosphate through pores formed by PhoE, OmpF and OmpC proteins shows that PhoE protein is the most effective pore in facilitating the diffusion of Pi and phosphorus-containing compounds. The three types of pores were about equally effective in facilitating the permeation of glucose and arsenate. Possible reasons for the preference for Pi and Pi-containing solutes are discussed.

Bacterial Outer Membrane Proteins↗
PubMed1986

31P-NMR spectroscopy demonstrates decreased ATP levels in vivo as an early response to photodynamic therapy.

31P-Nuclear magnetic resonance was used to monitor in situ phosphorus containing compounds in mammary tumors after photodynamic therapy, consisting of administration of hematoporphyrin derivative followed by photoradiation of the lesion. A rapid decrease in ATP along with an increase in Pi resonance intensities was observed. The beta-ATP/Pi ratio decreased by 1 hour, dropping in 2 to 8 hours to 0 to 20 percent of that found prior to photoradiation. Disrupted cells and pycnotic nuclei were observed 48 to 72 hours after photoradiation to a depth of approximately 5 mm. Together with previous studies in vitro, reduction in tumor ATP levels appears to be an early biochemical response to photodynamic therapy.

Adenosine Triphosphate↗
PubMed1995

HPLC and 31P NMR characterization of the reaction between antitumor platinum agents and the phosphorothioate chemoprotective agent S-2-(3-aminopropylamino)ethylphosphorothioic acid (WR-2721).

In prior studies, we examined the effects of the radioprotective and chemoprotective agent WR-2721 [S-2-(3-aminopropylamino)ethylphosphorothioic acid] on the in vivo biotransformation of the cisplatin [cis-diamminedichloroplatinum(II)] analog ormaplatin [(d,I)trans-1,2-diaminocyclohexanetetrachloroplatinum(IV), Pt(dach)Cl4, (formerly called tetraplatin)]. Those data suggested that a direct interaction between WR-2721 and ormaplatin and/or the corresponding Pt(II) drug, Pt(dach)Cl2, may be occurring in vivo. This would be in contrast to the generally accepted hypothesis that WR-2721 is a prodrug that must first be converted by alkaline phosphatase to a free thiol compound, WR-1065, before any appreciable reactivity would be evident. However, the major biotransformation product observed in the peritoneal fluid, plasma, and all tissues was Pt(dach)(WR-1065). We report here on further investigations into the in vitro reactivity of Pt(dach) compounds with WR-2721 and WR-1065. Separation of reaction products resulting from incubation of Pt(dach)(malonato) with either WR-2721 or WR-1065 under physiological conditions gave profiles that were indistinguishable by reverse phase HPLC and cation exchange HPLC at two different pHs. 31P NMR characterization of the dephosphorylation of WR-2721 revealed essentially no loss of inorganic phosphate for up to 24 hr when incubated in unbuffered water at 30 degrees. In contrast, when incubated with a 1:1 molar ratio of cisplatin under the same conditions, the WR-2721 signal was decreased markedly in the first 5 min, and had disappeared almost completely by 1 hr. The signal corresponding to inorganic phosphate increased in parallel to the decrease in the WR-2721 signal. No intermediate formation of a complex containing both platinum and phosphate could be detected at any time. These data suggest that the reaction between WR-2721 and platinum complexes results in rapid dephosphorylation of WR-2721, and, consequently, that the reaction products formed with either WR-2721 or WR-1065 and Pt(II) complexes are identical.

Amifostine↗
PubMed1990

32P-postlabelling of 7-methyl-dGMP ring-opened 7-methyl-dGMP and platinated dGpdG.

The 32P-postlabelling technique introduced by Randerath and coworkers was used to investigate the efficiency of the phosphorylation reaction by T4 polynucleotide kinase using three synthesized adducts: 7-methyl-dGMP, ring-opened 7-methyl-dGMP and platinated dGpdG. The methylated substrates were detected at sub-fmol sensitivities. 7-Methyl-dGMP was quantitatively phosphorylated at these low concentrations. The efficiency of phosphorylation of the ring-opened product was less (about one order of magnitude) and that of Pt(dGpdG) about three orders of magnitude less. These results show that T4 polynucleotide kinase phosphorylation is an efficient reaction with 7-methyl-dGMP and with ring-opened 7-methyl-dGMP, even though in the latter case longer incubation times may have to be used to boost the reaction towards completion. By contrast, the low level of phosphorylation with Pt(dGpdG) does not appear encouraging for quantitative determination requiring a high sensitivity.

Deoxyguanine Nucleotides↗
PubMed1991

32P-postlabeling of N-7, N2 and O6 2'-deoxyguanosine 3'-monophosphate adducts of styrene oxide.

Adducts were prepared by reacting styrene oxide with 2-deoxyguanosine 3'-monophosphate (dGMP). Four isomeric N-7-, two diastereomeric N2- and three isomeric O6-adduct were isolated and characterized. The adducts were used as substrates in the 32P-postlabeling reaction. No phosphorylation products were seen with the N-7-alkylation products. One diastereomeric N2-adduct was labeled with 20% efficiency and the second with a markedly lower efficiency. Two of the three O6-adducts were labeled with 5% and the third with 10% labeling efficiency. The results suggest that large N-7-dGMP adducts are very poor substrates of T4 polynucleotide kinase. The diastereomeric products are labeled at different efficiencies indicating stereoselectivity in the kinase reaction.

Deoxyguanine Nucleotides↗