PubMed · 1055564
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C D Leake. 1975-01-27. Opening remarks.. https://doi.org/10.1111/j.1749-6632.1975.tb25338.x
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Superoxide-driven reduction of alpha-tocopheroxyl radical in the presence of ubiquinone-10 has been demonstrated in dimethylsulfoxide. Our HPLC measurements showed that ubiquinone-10 protected alpha-tocopherol against oxidation by KO2 in a concentration-dependent manner. alpha-Tocopherol was oxidized by KO2 to form ESR-detectable radicals of tocopherol ubisemiquinone. In the presence of ubiquinone-10, neither these radicals nor alpha-tocopheroxyl radicals (generated by uv light or PbO2) could be detected in ESR spectra. Instead, ESR signals of ubisemiquinone-10 radicals were observed. Formation of ubisemiquinone-10 radicals from ubiquinone-10 upon addition of KO2 was ascertained by their characteristic ESR and uv-vis spectra. alpha-Tocopherol caused a concentration-dependent decrease of the ubisemiquinone-10 radical steady-state concentration. We conclude that one-electron reduction of ubiquinone-10 by superoxide ion resulting in the formation of ubiquinone-10 radicals caused redox-cycling of alpha-tocopherol from its phenoxyl radical, thus preventing loss of alpha-tocopherol. This suggests that coenzyme Q may have another physiological function, i.e., protection of alpha-tocopherol against superoxide-driven oxidation.
Two chlorate resistant mutants of Rhodobacter sphaeroides were isolated which were deficient in dimethylsulfoxide reductase activity. Immunoblotting experiments showed that the phenotype of these mutants and that of Rhodobacter capsulatus strain DK9, a mutant unable to reduce dimethylsulfoxide, was correlated with low or undetectable levels of the dimethylsulfoxide reductase apoprotein. All three mutants were complemented by a cosmid from a library of Rhodobacter sphaeroides genomic DNA. Further genetic complementation analysis revealed that functions required for restoration of dimethylsulfoxide reductase activity in the Rhodobacter sphaeroides mutants were encoded on an 9 kb EcoR1 DNA fragment derived from this cosmid. Expression of this 9 kb DNA fragment in Escherichia coli showed that it encoded the dimethylsulfoxide reductase structural gene of Rhodobacter sphaeroides.
This study has demonstrated that three hematopoietic tumor cell lines with megakaryocytic characteristics, HEL, CHRF-288-11, and K562, synthesize a number of sulfated proteins. The major HEL sulfated proteins were a doublet at 88 and 92 kDa and several closely spaced bands between 125 and 160 kDa and more acidic proteins of 210 kDa. Treatment with dimethylsulfoxide (DMSO) for 24 h almost completely inhibited labeling of sulfated proteins, and up to 48 h, labeling was found almost entirely in a band at 125 kDa. Treatment with phorbol 12-myristate 13-acetate (PMA) nearly eliminated labeling of the 88- and 92-kDa bands and resulted in the appearance of a large amount of labeling between 96 and 108 kDa. Sulfated proteins of 135 and 210 kDa were immunoprecipitated by an antibody against platelet GP Ib. A 130-kDa protein was immunoprecipitated by an antibody against the beta-1 integrin subunit. The major proteins labeled in CHRF cells were at 68, 90, 98, 125, and 148 kDa. Treatment with PMA greatly reduced the labeling of the 148-kDa band, eliminated the labeling of the 68-kDa band, and markedly enhanced labeling of the 92-kDa region. The major proteins labeled in K562 cells were at 110, 120-130, and 145 kDa. PMA reduced the labeling of the 110- and 145-kDa proteins and extensively increased labeling of bands at 120-130, 78, and 84 kDa, and DMSO caused decreased labeling of the 120- to 130-kDa proteins. This is the first demonstration of sulfation of specific proteins in hematopoietic cell lines and of the alteration of sulfation of specific proteins in any cells in response to treatment with differentiation-inducing agents. We hypothesize that changes in sulfation of proteins may be relevant to the maturation or malignant growth of megakaryocytic cells.