Characterization of Protease from the Myxosporean Salmon Parasite, Henneguya salminicola

Abstract

The biochemical properties of the protease(s) from the myxosporean parasite, Henneguya salminicola, occurring in the muscle of sockeye salmon, Oncorhynchus nerka, were examined. The cysts of the parasite contained a soluble, heat-labile protease, having maximal activity at pH 3.0 for hydrolysis of hemoglobin and 4.5 for hydrolysis of salmon muscle proteins. The inhibitions obtained from metal ions and from sulfhydryl group binding reagents suggest the involvement of sulfhydryl groups in the expression of enzyme activity. The enzyme required no preliminary activation by disulfide bond reducing agents and it had no obvious divalent metal ions requirement. The hydrolysis of salmon muscle by H. salminicola protease was strongly temperature dependent. Although proteolysis occurred at the highest rate at 30–40 °C, the enzyme remained active in iced muscle. The proteolytic activity was arrested completely in frozen muscle but the enzyme was only slightly inactivated by a prolonged frozen storage (−28 °C). The presence of the parasite had no marked effect on the texture of raw or cooked flesh.