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Enzyme fractions decomposing nucleic acid and related substances were isolated from the fruiting body of Matsu-take (Tricholoma matsutake), and they were partially purified by chromato- graphy using DEAE-Cellulose column.Ribonuclease (RNase) from Matsu-take had an optimum temperature of 60°C and a pH range of 7.0-7.5. The ranges of optimum temperature and pH of phosphodiesterase and phosphomono- esterase were 40-45°C and pH 6.0-6.5 and 40-45°C and pH 4.5-4.8, respectively.Yeast RNA was degraded by RNase fraction of Matsu-take under optimum condition for its activity, and four kinds of 5'-nucleotides, namely 5'-CMP, 5'-UMP, 5'-AMP and 5'-GMP were accumulated abundantly in its digest. The acid range-enzyme activities of fruiting bodies are different from those of Shii-take, and common mushrooms.

5'-IMP and related 5'-nucleotides are potent flavor substances contained in some foods. Sodium salts of 5'-IMF and other 5'-nucleotides were dissolved in distilled water or buffered solution and sealed in glass ampoules under atmosphere. The samples were irradiated with a 5, 000 curie cobalt-60 source at the dose rates of 2.3×103-3.6×105 r/hr at room temperature.The residual levels of 5'-IMP irradiated at 1.0 Mrad were 61 and 86% in distilled water and in buffer of pH 7 (Fig. 2), respectively. The decimal reduction dose at pH 7 was 17.2 Mrad. 5'-IMP was found to be more labile at pH 3 and 5 rather than at pH 7 and 9 (Fig. 3). Irradiation of 5'-IMP led to the splitting of the bond between nucleic base and ribose phosphate, resulting in the increase of hypoxanthine (Table 5 and 6).There is a significant difference between the mode of decomposition affected by heating and by γ-irradiation.Purine nucleotides are more stable than pyrimidine nucleotides against γ-irradiation (Table 3 and 4), but the formers are more labile than the latters against heating. Existence of sugar is protective against the destruction by γ-ray (Fig. 5) but is promotive of that by heat.