The accumulation of transcripts of mitochondrial genes in young buds was examined in euplasmic and alloplasmic lines of Brassica rapa for the 'mur' system of cytoplasmic male sterility (CMS). Southern blotting analysis revealed the general absence of restriction fragment length polymorphism between Diplotaxis muralis, the donor of cytoplasm, and each of three sterile alloplasmic lines, indicating that the rearrangement of mitochondrial DNA might not be caused by the nucleus of B. rapa. However, different Northern hybridization patterns were detected when coxI and nad3 were used as probes. Production of the 2.5-kb transcript of coxI and a reduction in levels of the transcript of nad3 in the sterile alloplasmic lines were clearly under the control of the nucleus of B. rapa. No such differences in patterns of transcripts were detected in the leaves. This observation suggests that some factor(s) or gene(s) in the nucleus of B. rapa acts in an organ-specific manner to alter the size of transcripts in the mitochondria of the donor cytoplasm without any structural changes in the mitochondrial genome. Further studies are required to clarify whether or not the unique transcripts in the young buds induce a CMS event.
Acetylpyridines (1-3) are known as aroma components of foods, perfumes, and smoking suppressants, showing several biological activities and constituting part of the structure of some important biologically active compounds. We purified and characterized an enzyme that catalyzes the stereoselective reduction of acetylpyridines so that we could clarify its function. The enzyme participating in the reductive metabolism of 4-acetylpyridine (1) in the rat liver was purified by successively applying ammonium sulfate fractionation, anion-exchange, gel filtration, and affinity chromatography, and it was definitively identified as 3alpha-HSD. It preferentially reduced acetylpyridines (1-3) and acetophenone (7) to their corresponding (S)-alcohols, with high enantioselectivity. Kinetic analyses of the compounds were performed, and the V(max)/K(m) values decreased in the order of 4-, 2-, and 3-acetylpyridine (1, 3, 2), while acetophenone (7) showed almost the same value as 3-acetylpyridine (2). These results suggested that the reduction of the substrates by 3alpha-HSD is affected by the nitrogen atom in the aromatic ring.
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