Characterization of protease activity from the digestive tract and tentacles of Isostichopus fuscus sea cucumber

Abstract

Sea cucumbers possess evisceration mechanisms and regeneration capacity. The function of tentacles is to collect food particles. From our results, we suggest these organs could also be part of the digestive system. Therefore proteases in the digestive tract and tentacles of Isostichopus fuscus were partially characterized by histological and biochemical methods. Digestive cells and regions, and secretory granules were observed by histological methods in both organs. Proteolytic extracts of the digestive tract and tentacles showed peak activity at pH 6 and 8. The digestive tract extract had peak activity at 40 and 70 °C, whereas the tentacle extract peak activity was at 60 °C. Both extracts showed activity at 0 to 10 °C. The extracts retained 67 to 75 % residual activity when incubated at 60 °C for 1 h. The effect of different ions and specific inhibitors suggested the presence of cysteine- and metallo-proteases in both organs. SDS-PAGE showed 6 proteins of approximately 40, 43, 49, 76, 106, and 147 kDa in the digestive tract extract, and 5 proteins of approximately 44, 60, 81, 108, and 150 kDa in the tentacle extract. Native-PAGE and zymography assays confirmed the presence approximately 100 kDa proteases in both extracts. The tentacle extract had the highest proteolytic activity, suggesting that this organ could contribute to the digestion process of I. fuscus. 

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