Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In order to understand the thermodynamic state of simple salts in living cells, the mean activity coefficients of LiCl, NaCl, KCl, RbCl, CsCl were determined in concentrated isoionic bovine serum albumin (BSA) solutions by use of the EMF method with ion exchange membrane electrodes. The protein concentration range extended up to 22 wt%, whereas the salt concentration was kept constant at 0.1 mole per kilogram water. These solutions may be regarded as crude but appropriate model systems for the cytoplasm of cells as far as type and magnitude of the macromolecular component influence on the chemical potential of the salts is concerned. The mean stoichiometric activity coefficients of the alkali chlorides in the isoionic BSA solutions decreased linearly with the protein molality; this decrease, however, did not exceed ca. 10% compared with the pure 0.1 molal salt solutions. Only very small differences in the behavior of the different alkali chlorides were observed. The results may be interpreted by the superposition of the effects of specific Cl- ion binding to BSA and BSA bound "non-solvent" water with probably electrostatic long range interactions of the BSA(Cl-)nu polyions with the salt ions in solution. The resulting mean activity coefficients, corrected for ion binding and non-solvent water, showed a very slight linear dependence on the protein concentration. The departure from the value in the pure 0.1 molal salt solutions did not exceed +/- 2%.
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PMID:Activity coefficients of salts in highly concentrated protein solutions. I. Alkali chlorides in isoionic bovine serum albumin solutions. 75 2

The ATPase subunit of the osmoregulatory ATP-binding cassette transporter OpuA from Lactococcus lactis has a C-terminal extension, the tandem cystathionine beta-synthase (CBS) domain, which constitutes the sensor that allows the transporter to sense and respond to osmotic stress (Biemans-Oldehinkel, E., Mahmood, N. A. B. N., and Poolman, B. (2006) Proc. Natl. Acad. Sci. U. S. A. 103, 10624-10629). C-terminal of the tandem CBS domain is an 18-residue anionic tail (DIPDEDEVEEIEKEEENK). To investigate the ion specificity of the full transporter, we probed the activity of inside-out reconstituted wild-type OpuA and the anionic tail deletion mutant OpuADelta12; these molecules have the tandem CBS domains facing the external medium. At a mole fraction of 40% of anionic lipids in the membrane, the threshold ionic strength for activation of OpuA was approximately 0.15, irrespective of the electrolyte composition of the medium. At equivalent concentrations, bivalent cations (Mg(2+) and Ba(2+)) were more effective in activating OpuA than NH(4)(+), K(+), Na(+), or Li(+), consistent with an ionic strength-based sensing mechanism. Surprisingly, Rb(+) and Cs(+) were potent inhibitors of wild-type OpuA, and 0.1 mM RbCl was sufficient to completely inhibit the transporter even in the presence of 0.2 M KCl. Rb(+) and Cs(+) were no longer inhibitory in OpuADelta12, indicating that the anionic C-terminal tail participates in the formation of a binding site for large alkali metal ions. Compared with OpuADelta12, wild-type OpuA required substantially less potassium ions (the dominant ion under physiological conditions) for activation. Our data lend new support for the contention that the CBS module in OpuA constitutes the ionic strength sensor whose activity is modulated by the C-terminal anionic tail.
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PMID:Ion specificity and ionic strength dependence of the osmoregulatory ABC transporter OpuA. 1684 87

Biological ion channels are proteins that passively conduct ions across membranes that are otherwise impermeable to ions. Here, we present a model of ion permeation and selectivity through a single, open ryanodine receptor (RyR) ion channel. Combining recent mutation data with electrodiffusion of finite-sized ions, the model reproduces the current/voltage curves of cardiac RyR (RyR2) in KCl, LiCl, NaCl, RbCl, CsCl, CaCl(2), MgCl(2), and their mixtures over large concentrations and applied voltage ranges. It also reproduces the reduced K(+) conductances and Ca(2+) selectivity of two skeletal muscle RyR (RyR1) mutants (D4899N and E4900Q). The model suggests that the selectivity filter of RyR contains the negatively charged residue D4899 that dominates the permeation and selectivity properties and gives RyR a DDDD locus similar to the EEEE locus of the L-type calcium channel. In contrast to previously applied barrier models, the current model describes RyR as a multi-ion channel with approximately three monovalent cations in the selectivity filter at all times. Reasons for the contradicting occupancy predictions are discussed. In addition, the model predicted an anomalous mole fraction effect for Na(+)/Cs(+) mixtures, which was later verified by experiment. Combining these results, the binding selectivity of RyR appears to be driven by the same charge/space competition mechanism of other highly charged channels.
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PMID:(De)constructing the ryanodine receptor: modeling ion permeation and selectivity of the calcium release channel. 1685 78