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To apply an irradiation technique to sterilize “Hybrid” biomedical materials including enzymes, we selected papain, a well-characterized plant endopeptidase as a model to examine durability of enzyme activity under the practical irradiation condition in which limited data were available for irradiation inactivation of enzymes. Dry powder and frozen aqueous solution of papain showed significant durability against 60 Co-gamma irradiation suggesting that, the commercial irradiation sterilizing method is applicable without modification. Although irradiation of unfrozen aqueous papain solution showed an unusual change of the enzymatic activity with the increasing doses, and was totally inactivated at 15 kGy, we managed to keep the residual activity more than 50% of initial activity after 30-kGy irradiation, taking such optimum conditions as increasing enzyme concentration from 10 to 100 mg/ml and purging with N 2 gas to suppress the formation of free radicals.

The profit-sharing model has attracted considerable attention as a hypothesis to explain wage flexibility and employment stability in Japan. This paper presents an alternative explanation of how bonuses and basic wages are determined in Japan, based on the efficiency wage hypothesis. In particular, we focus on the aspect that bonuses are paid to compensate employees for the intensity of work experienced during the last period, and basic wages are affected mainly by labor market conditions and are not firm-specific. We compare the two models, testing them for both industry aggregate data and firm microdata.