Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P50583 (asymmetrical)
 12,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Temperature-induced conformational changes in the anticodon region of yeast tRNATyr were studied by EPR spectroscopy. The spin label 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl was attached to the N6-(delta2-isopentenyl)-adenosine residue in tRNATyr, previously made reactive by iodination. The labelled tRNATyr gave an asymmetrical triplet spectrum typical of rapidly tumbling nitroxide, with a rotational correlation time (tauc) of 0.65 ns. Spin-labelled tRNATyr was exposed to heating and cooling in three different buffers each with or without MgCl2. In each case the Arrhenius plot of --log tauc vs. inverse absolute temperature gave two straight lines, intersecting at a critical temperature (tcr). Above tcr, the anisotropy of the spectrum was not reduced and the activation energy of motion increased, indicating that the transition is associated with a conformational change of the macromolecule. Transitions in 0.05 M potassium phosphate (pH 8.0) and 0.02 M Tris - HC1 (pH 7.0) were observed at potassium phosphate (pH 8.0) and 0.02 M Tris - Hc1 (pH 7.0) were observed at approx. 37 degrees C. When 0.01 M mgCl2 was present in these buffers, transitions were shifted to 46 degrees and 53 degrees C, respectively. Transitions in 0.01 M sodium cacodylate were observed at temperatures which are significantly lower. Since all these transitions occur at temperatures considerably below those required to melt the helical regions of tRNA, and at least approximately 10 degrees C below those reported to break tertiary interactions, it is supposed that they reflect some reorientation of the anticodon region, e.g. a change in tilt of the bases.
 ...
PMID:Conformational changes in yeast tRNATyr revealed by EPR spectra of spin-labelled N6-(delta2-isopentenyl)-adenosine residue. 20 Feb 69

A 3 Na/Ca exchanger in the transverse tubular wall is modelled as the coupling mechanism between transverse tubular depolarization and Ca release from the sarcoplasmic reticulum. At rest, the Ca-occupied site faces the transverse tubular lumen. Upon depolarization, the difference in chemical potentials of Na and Ca gives a net inward force on Ca resulting in a reorientation of the exchanger so the Ca site now faces the myoplasm and releases Ca to stimulate Ca-induced Ca release from the sarcoplasmic reticulum. The rotation of the exchanger's asymmetrical charge could generate the 'charge movement' signal. As depolarization continues, the site is depleted of Ca and contraction ends spontaneously. Repolarization reorients the exchanger; the depleted Ca site now faces the transverse tubular lumen and slowly refills with Ca (repriming). A kinetic model is capable of controlling both twitch and contracture tension. The Na/Ca exchange blocker dichlorobenzamil (Merck) (10 microM), elevated external Na and low pH all slowed the rate of rise of potassium contracture tension. The ratios of rates of tension rise were dCB/control = 0.4 +/- 0.1, elevated external Na/Tris = 0.6 +/- 0.1, pH 6.3/control = 0.7 +/- 0.01. These results can be mimicked with the kinetic model by slowing the rate of 'rotation' (and hence charge movement) by 50%. Elevated internal Na increases the rate of rise of contracture tension; elevated internal Na/control 1.6 +/- 0.3. Dichlorobenzamil also slows the recovery following spontaneous relaxation; the time constant (68 s) of repriming is unchanged but shifted to longer recovery times. Reduced external Na and pH 6.3 also slow recovery in a similar manner, consistent with delayed rotation of the Ca-depleted site. These results suggest that Na/Ca exchange is a step in both the excitation contraction coupling chain and the repolarization-repriming sequence.
 ...
PMID:Na/Ca exchange and excitation--contraction coupling in frog fast fibres. 321 96

A solution-phase procedure using an orthogonal protection scheme was developed for the synthesis of a novel family of multi-pegylating reagents. The procedure was exemplified by the synthesis of bis- and tris-pegylating reagents prepared by stepwise insertion of the poly(ethylene glycol) units thereby enabling the preparation of both symmetrical and asymmetrical pegylating reagents. Asymmetrical pegylation and tris-pegylation of peptides and proteins introduces new variables for use in the optimization of pegylated peptides and proteins. These reagents are ideally suited for conjugation to peptides and proteins as they possess a required functional group and will be useful intermediates for the synthesis of a new generation of pegylated products. Tris-pegylation can also provide more effective protection from proteolysis by shielding the protein surface from approaching macromolecules. To illustrate this potential, conditions were developed for the successful coupling of the tris-pegylating reagent to a model pentapeptide.
 ...
PMID:Synthesis of symmetrically and asymmetrically branched pegylating reagents. 1500 29

Tris(2,3,5,6-tetrathiaaryl)methyl cations, which were generated from the corresponding triarylmethanols in the presence of strong acids, underwent reaction with nucleophiles to give trityl radicals, as the product of a one-electron reduction of the carbocation. Depending on the nature of the nucleophile, the only byproducts were either diamagnetic quinone methides or asymmetrical monosubstituted trityl radicals. Herein, we report a protocol for the large-scale synthesis of the Finland trityl, which has the advantage of high overall yield and reproducibility.
 ...
PMID:Generation of Trityl Radicals by Nucleophilic Quenching of Tris(2,3,5,6-tetrathiaaryl)methyl Cations and Practical and Convenient Large-Scale Synthesis of Persistent Tris(4-carboxy-2,3,5,6-tetrathiaaryl)methyl Radical. 2477 1