PubMed · 13095034
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H MATTHIES. 1953-09-03. [Methemoglobin decrease and cation transfer in erythrocytes].. https://pubmed.ncbi.nlm.nih.gov/13095034/
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The M2 protein form influenza A virus forms a tetrameric ion channel, which enables proton passage across biological membranes when the N-terminal side is acidified. Among the amino acid residues in the transmembrane domain of the M2 protein, His37 and Trp41 are essential for the pH-regulated proton conductance. Current knowledge about the structures and interactions of His37 and Trp41 suggests a model for the M2 ion channel, in which the channel is closed by a network of His37 hydrogen bonds at neutral pH and is opened by a His37-Trp41 cation-pi interaction at acidic pH.
The reaction of H2O2 with thioanisole and p-methoxythioanisole catalysed by lignin peroxidase from Phanerochaete chrysosporium has been studied spectrophotometrically under turnover and single turnover conditions with a stopped-flow apparatus. Pre-formed lignin peroxidase compounds I and II are each able to react with the sulphides to form a sulphide radical cation. The radical cation is then converted into the sulphoxide either by reaction with the medium or by reaction with compound II. This is the first report of a direct reaction between compound II and the substrate radical cation. With thioanisole, significant enantiomeric selectivity and high oxygen incorporation in the sulphoxide are obtained because compound II is preferentially reduced by the enzyme-bound thioanisole radical cation compared with the neutral substrate. By contrast, with p-methoxythioanisole, the data imply formation of an intermediate ternary complex comprising compound II, radical cation and neutral substrate, such that a chain of electron transfer reactions starting from neutral molecule and progressing to oxidized haem via substrate radical cation is facilitated, yielding the native enzyme and two molecules of p-methoxythioanisole radical cation as products. The reactions of compounds I and II with sulphides imply flexing of the apoprotein moiety during catalysis.
In whole-cell recordings on single HeLa cells, the hypertonic activation of a cation conductance with a selectivity ratio P(Na):P(Li):P(K):P(Cs):P(NMDG):P(Ca):P(Cl) of 1.00:0.86:0.84:0.56:0.10:0.07:0.15 was observed. This (non-selective) cation conductance was reduced to 59 and 30% of maximal stimulation by Gd(3+) and flufenamate, respectively, but it was insensitive to amiloride (with each compound applied at 100 microm/l). As was determined by the Coulter counter technique, the cation conductance was the main mechanism of regulatory volume increase (RVI) in HeLa cells. Whereas a significant contribution of Na(+)/H(+) antiport was also detectable, Na(+)-K(+)-2Cl(-) symport most likely did not contribute to RVI.