PubMed · 5725220
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C J Pedersen. Ionic complexes of macrocyclic polyethers.. https://pubmed.ncbi.nlm.nih.gov/5725220/
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The phosphorylation and dephosphorylation of the 25 kDa mRNA cap binding protein eukaryotic initiation factor-4E (eIF-4E) is regulated during different physiologic and pathophysiologic states that include cell growth and the late phase of adenovirus infection. We have found that okadaic acid is much more effective in increasing the phosphorylated fraction of eIF-4E than phorbol 12-myristate 13-acetate in Hep G2 cells. Phosphoprotein phosphatase 2A dephosphorylated eIF-4E isolated from both phorbol 12-myristate 13-acetate- or okadaic acid-treated cells, whereas alkaline and acid phosphatase were relatively ineffective. The ability of purified [35S]eIF-4E isolated from okadaic acid-treated cells to bind mRNA caps was compared to phosphoprotein phosphatase 2A-treated [35S]eIF-4E and found to be no different. This suggests that alternative explanations for the previously observed effects of eIF-4E phosphorylation on protein synthesis must be considered. In addition, our results indicate that the in vivo phosphorylation of eIF-4E is not catalyzed solely by protein kinase C.
Structures of 8-(2-hydroxyethyl)pterins (8-11) investigated using 1H- and 13C-NMR and UV/vis spectroscopies showed a complex dependence on pH, solvent and 6,7-substitution pattern. In acid, only one cation was observed for all the pterins. In neutral aqueous solution, only one neutral form, the normal quinonoid tautomer, was observed for 7-unsubstituted pterins 9 & 11, but two neutral tautomeric forms, quinonoid and 7-exo-methylene, were observed for 7-CH3 substituted pterins 8 & 10 with 70% and 92%, respectively, of quinonoid. The neutral pterins in MeOH, however, showed a different distribution of structural forms: quinonoid and a five-membered intramolecular ether forms were observed for 7-unsubstituted pterins 9 & 11 as 60% and 25%, respectively, of quinonoid, while quinonoid and 7-exomethylene forms were observed for 7-CH3 substituted pterins 8 & 10 as 10% and 50%, respectively, of quinonoid. In base, for 7-unsubstituted pterins 9 & 11 only the intramolecular ether forms were observed, while for the 7-CH3 substituted pterins 8 & 10 two anion forms, the 7-exo-methylene and intramolecular ether, were observed in the ratio 2:1. Investigation of the distinctive proton-resonance pattern of the ethanomoiety of the intramolecular ether anion of 9 using 600 MHz NMR and spectrum simulation, indicated all four protons have different chemical environments. One conformation of the cyclic-ether ring satisfying the experimental data has been deduced, and the conformational energetics of the ring studied further using AM1 semiempirical quantum chemical calculations. Structural distributions of 8-methylpterins 12-15 were also studied in base only. These showed the 7-unsubstituted pterins 13 & 15 existed solely as the hydrated anion forms, while the 7-CH3 substituted pterins 12 & 14 existed predominantly as the 7-exo-methylene anions. Spectroscopic investigations of the degradation processes of 8-(2-hydroxyethyl)pterins and 8-methylpterins in base indicated a complex pattern of oxidation, ring opening and elimination reactions as a function of time. Using authentic samples, the 7-oxo compounds 16 & 17 and ethanolamine were identified, and evidence for ring-opened forms was obtained by comparison with the relevant 2,5-diamino-6-alkyl-aminopyrimidin-4(3H)-ones 1 & 2. Characteristically different degradation pathways for 7-CH3 and 7-unsubstituted compounds were established.
With a Nicolet 20 SX B Fourier Transform infrared spectrometer, the mid-infrared spectra in region of 4000-400 cm-1 were observed for a series of benzocrown ether and macrocyclic polyether diester. A difference in the wavelength of absorption of the ether bond was found between benzocrown ether and macrocyclic polyether diester. The wavelength of absorption of the ether bond of the compounds I-IV moved down about 25 cm-1, as compared with that of the compounds V-IX.