IDENTIFICATION OF NEW SPECIES OF BRAIN-SPECIFIC CYTOCHROME b_5

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In this research project we tried to identify new species of brain-specific cytochrome b_5 from human and mouse brain cDNA library. By plaque hybridization method we screened total of 5x10^5 plaques of mouse brain cDNA library using ECL 3'-oligolabelled primer and random-labelled cDNA of human liver. We obtained 16 clones hybridized with 3'-oligolabelled primers, and 18 clones with random-labelled cDNA. Among them 4 clones gave common signals with both probes, and other clones were all different. Isolation of insert DNAs for analyzing the base sequences of these clones are now proceeding.In parallel with the screening the cDNA for new species for brain-specific cytochrome b_5 we analyzed the distribution of cytochrome b_5 in rat brain immunohistochemically using anti-cytochrome b_5. Cytochrome b_5 was found to localize to both white and gray matters, but especially to neuronal cells in gray matter. This is a sharp contrast to the distribution of cytochrome P-450 in brain which was shown to localize selectively to myelinated fibers in white matter. Such a clear difference in the distributions of cytochrome P-450 and cytochrome b_5 in brain tissues observed in this study is the first example.These results apparently indicate that it is important to identify the structure of and to analyze the functions of brain-specific cytochrome b_5s. Some species of brain-specific cytochrome b_5 may deeply participate in the function of neuronal cells in gray matter.