Mulberry 1-deoxynojirimycin (DNJ), a potent glucosidase inhibitor, has been hypothesized to be beneficial for the suppression of abnormally high blood glucose levels and thereby prevention of diabetes mellitus. However, DNJ contents in commercial mulberry products were as low as about 0.1% (100 mg/100 g of dry product), implying that the bioavailability of DNJ might not be expected. We carried out studies in two directions: (1) production of food-grade mulberry powder containing a maximally high DNJ content; (2) determination of the optimal dose of the DNJ-enriched powder for the suppression of the postprandial blood glucose through clinical trials. The following method was used: (1) DNJ concentrations in mulberry leaves from different cultivars, harvest seasons, and leaf locations were determined using hydrophilic interaction chromatography with evaporative light scattering detection. (2) Healthy volunteers received 0, 0.4, 0.8, and 1.2 g of DNJ-enriched powder (corresponding to 0, 6, 12, and 18 mg of DNJ, respectively), followed by 50 g of sucrose. Before and 30-180 min after the DNJ/sucrose administration, plasma glucose and insulin were determined. The following results were obtained: (1) Young mulberry leaves taken from the top part of the branches in summer contained the highest amount of DNJ. After optimization of the harvesting and drying processes for young mulberry leaves (Morus alba L. var. Shin ichinose), DNJ-enriched powder (1.5%) was produced. (2) A human study indicated that the single oral administration of 0.8 and 1.2 g of DNJ-enriched powder significantly suppressed the elevation of postprandial blood glucose and secretion of insulin, revealing the physiological impact of mulberry DNJ (effective dose and efficacy in humans). This study suggests that the newly developed DNJ-enriched powder can be used as a dietary supplement for preventing diabetes mellitus.

A gene that confers resistance to the systemic fungicide flutolanil was isolated from a mutant strain of the basidiomycete Coprinus cinereus. The flutolanil resistance gene was mapped to a chromosome of approximately 3.2 Mb, and a chromosome-specific cosmid library was constructed. Two cosmid clones that were able to transform a wild-type, flutolanil-sensitive, strain of C. cinereus to resistance were isolated from the library. Analysis of a subclone containing the resistance gene revealed the presence of the sdhC gene, which encodes the cytochrome b560 subunit of the succinate dehydrogenase (SDH) complex (Complex II) in the mitochondrial membrane. Comparison between the sdhC gene of a wild-type strain and that of a mutant strain revealed a single point mutation, which results in the replacement of Asn by Lys at position 80. Measurements of succinate-cytochrome c reductase activity in the transformants with mutant sdhC gene(s) suggest that flutolanil resistance of the fungus is caused by a decrease in the affinity of the SDH complex for flutolanil. This sdhC mutation also conferred cross-resistance against another systemic fungicide, carboxin, an anilide that is structurally related to flutolanil. In other organisms carboxin resistance mutations have been found in the genes sdhB and sdhD, but this is the first demonstration that a mutation in sdhC can also confer resistance. The mutant gene cloned in this work can be utilized as a dominant selectable marker in gene manipulation experiments in C. cinereus.

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