ふなずしの熟成における筋肉カテプシンＤの関与

Abstract

It is said that both autolysis of fish meat and lactic acid fermentation of boiled rice participate in the ripening of Funazushi (fermented seafood made of crucian carp Carassius auratus). However, there has been no study on the autolysis of Funazushi. It is also said that during ripening, the NaCl concentration of fish meat decreases to about 2% and pH falls below 5.0. Therefore we separated and purified catchepsin D (EC 3.4. 23.5), which is an acid pro-teinase, from a gengoro-crucian carp muscle, and examined the enzymatic properties to elucidate whether it participates in the ripening of Funazushi. The cathepsin D purified from crucian carp muscle using a combination of ammonium sulfate and acetone fractionations, DEAE-cellulose, and hydroxylapatite chromatographies, Ultrogel AcA34 and AcA44 gel filtrations was stable at pH 2.2-6.0 at room temperature as well as at 30°C and pH 3.0. Although the enzyme lost almost all activity in the presence of NaCl above 0.3M (1.8%), it restored the activity after removing NaCl. The enzyme hydrolyzed myofibrillar proteins such as myosin heavy chain, actin, tropomyosin in the presence of 2.3% NaCl at pH 5.0. From these results, the enzyme was considered to be one of factors participating in the ripening of Funazushi.