We have been studying various bioactive compounds produced by mushrooms. In this review, endoplasmic reticulum (ER)-stress suppressors from Hericium erinaceus, Mycoleptodonoides aitchisoni, Termitomyces titanicus, Leccinum extremiorientale and Stropharia rugosoannulata, osteoclast-formation suppressors from Agrocybe chaxingu, and Grifola gargal, plant growth regulators from Lepista sordida and Agrocybe praecox, toxins from Boletus venenatus and Pleurocybella porrigens, and lectins from Hygrophorus russula and Pholiota squarrosa are discussed.

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Glutamic acid decarboxylase (GAD) [EC 4.1.1.15], an enzyme involved in accumulation of GABA by edible mushrooms, was purified from fruiting bodies of Grifola frondosa, and its properties were characterized. The GAD enzyme was purified 11.9-fold, with a yield of 1.24%, and showed a single band on SDS-PAGE. The molecular mass of purified GAD was 42 kDa based on SDS-PAGE and 97 kDa based on HPLC-GPC. These results indicate that the enzyme consists of 2 identical subunits. Maximum activity was observed at 37℃ at a pH value of 3.5. The enzyme was stable at 37℃ for 30 min and in the pH range 2.5-5.5. GAD isolated from G. frondosa was specific for _L-glutamate. The K_m and V_<max> of the enzyme were calculated to be 7.5 mM and 450 μmol min^<-1>, respectively. The enzyme activity was strongly inhibited by HgCl_2 and AgNO_3 (0% and 32% of activity in the absence of inhibitors, respectively).

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In this study, we produced miso using edible and medicinal mushrooms instead of Aspergillus oryzae. We measured protease activities of 14 strains of mushrooms in the presence of salt. Eleven strains of mushrooms, such as Isaria cicadae NBRC 33259, showed high productivity of salt-tolerant protease. We attempted miso production using these 11 strains of mushrooms. After 28 days of fermentation, all samples had changed into a soft paste similar to miso. The nutrient composition of this mushroom miso was similar to that of commercial miso. The soluble nitrogen content of Pleurotus salmoneo-stramineus miso was 8.46 g/kg, while that of commercial miso was 8.32 g/kg. The formol nitrogen content of Flammulina velutipes miso was 4.42 g/kg, and that of commercial miso was 3.67 g/kg. Finally, we assayed the amino acid composition of mushroom miso and found that glutamic acid content in 5 strains of mushroom miso was higher than that in commercial miso.

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Chitosan is a polysaccharide produced by deacetylation of chitin in mushroom cell walls and exoskeletons of crustaceans. In this study, we examined the effects of mushroom chitosan (chitosan made from Flammulina velutipes) on hyperlipidemia and obesity in an animal obesity model comprising Zucker fatty rats. Mushroom chitosan administered to Zucker fatty rat groups led to a significant reduction in body weight, as well as a decrease of lipid accumulation in liver and an increased lipid excretion rate in feces. Triglyceride, total cholesterol and LDL-cholesterol levels decreased significantly as shown by blood biochemical testing. Mushroom chitosan also led to improvement of blood lipid metabolism and inhibition of lipid accumulation in the liver. The mechanism of these effects involved both inhibition of lipid absorption from the intestine and lipolysis in adipose cells. Our results suggest that mushroom chitosan is effective for reducing the risk of both obesity and metabolic syndrome.

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We examined the brightness of the fruit bodies of Shiitake (Lentinula edodes), Maitake (Grifola frondosa) and Hiratake (Pleurotus ostreatus) to survey the longevity of freshness after soaking them in trehalose solutions of 1%, 3%, 5% and 7% with decompression. Three kinds of fruit bodies were purchased from two cultivators, and they were kept at 5℃, 15℃ and 25℃ for 10 days after soaking. Positive effects of trehalose were shown on Shiitake from one cultivator when the fruit bodies were kept at 15℃ and 25℃ and on Maitake from both cultivators when the fruit bodies were kept at 15℃ or 25℃. For Hiratake, no positive effect was clear for fruit bodies obtained from either cultivator, except for the fruit bodies from one cultivator that were kept at 25℃.

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