Characterization and Expression Levels of Protease Enzymes at Different Developmental Stages of Siamese Fighting Fish (Betta splendens Regan, 1910)

Abstract

Characterization of total proteases, trypsin and chymotrypsin were performed at pH 2 12 and\ntemperatures 20-80°C in three life stages of Siamese fighting fish (Betta splendens Regan, 1910). At\nleast fourteen protease activities were detected, including seven acidic (pH levels 2, 4 and 5-6), one\nneutral (pH 7), and six alkaline (pH levels 8-12) activities in the optimal temperature range of 30-60°C.\nThe neutral and alkaline pH profiles were different between sexes during the on-growing stage (1.5\nmonth-old). The acidic proteases played a major role in digestion in the early life stage (10-day-old),\nwhile the alkaline proteases became more important toward older stages. Trypsin and chymotrypsin\nshowed similar characteristics with at least five activities observed. For trypsin, activity was detected\nwith pH 7 and 8 at 50°C, and pH 10 at 30, 50 and 60°C. For chymotrypsin, activity was found at pH\nlevels 7 and 8 at 50°C, and pH 10 at 30, 40 and 50°C. Regardless of sex and age, the most suitable\nconditions for studying digestive enzyme activities in general were at pH 8 and 50°C for total proteases,\npH 7-8 and 50°C or pH 10 and 30-35°C for trypsin and pH 7-8 and 50°C or pH 10 and 40°C for\nchymotrypsin. Trypsin and chymotrypsin are important proteases showing similar general optimal\nconditions to that of total proteases. This information provides elementary knowledge for studying\nprotein digestibility by in vitro techniques and for determining growth performance quality using digestive\nenzyme markers in Siamese fighting fish.