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J M Nocek D M Kurtz R A Pickering M P Doyle 《The Journal of biological chemistry》1984,259(20):12334-12338
In anaerobic phosphate buffer, pH 6.3-7.5, deoxyhemerythrin is oxidized to semi-methemerythrin (semi-met) by excess sodium nitrite. This oxidation is quantitative as judged by EPR spectroscopy. Further oxidation to methemerythrin is not detected. The absorbance changes of hemerythrin during the oxidation are biphasic. The rate of the faster first phase is linearly dependent on [H+] and [NO2-] suggesting that the oxidant is nitrous acid rather than nitrite. During the slower second phase, the characteristic EPR spectrum of semi-methemerythrin appears. The first phase can be interpreted by a scheme in which nitrous acid transforms deoxyhemerythrin (FeIIFeII) to the semi-met nitrosyl adduct (FeIIFeIIINO) and hydroxide. Independent experiments confirm that the combination of semi-met plus NO produces an EPR-silent adduct. The rates of the absorbance changes for the second phase are nearly independent of nitrite concentration and pH in the range 6.3-7.5. This slower phase involves the transformation of the EPR-silent intermediate to the semi-met nitrite adduct (FeIIFeIIINO2-) and is consistent with rate-limiting dissociation of nitric oxide followed by rapid attachment of nitrite. Nitrite appears to be a unique oxidant of deoxyhemerythrin in that when employed in excess, the final, stable product is semi-met- rather than methemerythrin. The lack of reactivity of ethyl nitrite with deoxyhemerythrin suggests that HONO oxidizes deoxyhemerythrin via an "inner-sphere" process in contrast to oxidants such as Fe(CN)6(3-). A proposed generalization is that excesses of "inner-sphere" oxidants convert deoxy to (semi-met)R, which is stabilized with respect to (semi-met)R, which is stabilized with respect to (semi-met)0 and met because the oxidant and/or a product of the oxidant can bind to the iron site. 相似文献
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The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from
nucleotide sequence variation across a 765-bp region in the cytochrome
oxidase I and II genes of the mitochondrial genome. Most parsimonious
relationships of 25 haplotypes from 16 Greya species and two outgroup
genera (Tetragma and Prodoxus) showed substantial congruence with the
species relationships indicated by morphological variation. Differences
between mitochondrial and morphological trees were found primarily in the
positions of two species, G. variabilis and G. pectinifera, and in the
branching order of the three major species groups in the genus. Conflicts
between the data sets were examined by comparing levels of homoplasy in
characters supporting alternative hypotheses. The phylogeny of Greya
species suggests that host-plant association at the family level and larval
feeding mode are conservative characters. Transition/transversion ratios
estimated by reconstruction of nucleotide substitutions on the phylogeny
had a range of 2.0-9.3, when different subsets of the phylogeny were used.
The decline of this ratio with the increase in maximum sequence divergence
among taxa indicates that transitions are masked by transversions along
deeper internodes or long branches of the phylogeny. Among transitions,
substitutions of A-->G and T-->C outnumbered their reciprocal
substitutions by 2-6 times, presumably because of the approximately 4:1
(77%) A+T-bias in nucleotide base composition. Of all transversions,
73%-80% were A<-->T substitutions, 85% of which occurred at third
positions of codons; these estimates did not decrease with an increase in
maximum sequence divergence of taxa included in the analysis. The high
frequency of A<-->T substitutions is either a reflection or an
explanation of the 92% A+T bias at third codon positions.
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