Seasonal changes in the thyroid proteinase of a teleost fish, the burbot, Lota lota L.

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Abstract
Proteolytic activity extracted from thyroid tissue was studied over the course of a year. The pH curves of enzyme prepared from fish collected in winter and spring were basically alike and showed three peaks of activity. The thermal stabilities, Michaelis constants, and iodoacetate sensitivity suggest that the enzymes prepared from fish in winter and spring were different. Furthermore, the ratios of activities at the three peak pH values are not constant.The proteolytic activity assayed at the optimum pH 2.5 showed a significant increase in June.