Comparative enzyme activities of the intestinal brush border membranes of the herbivorous mudskipper Boleophthalmus pectinirostris and the carnivorous Chinese black sleeper Bostrichthys sinensis

P>Both the mudskipper Boleophthalmus pectinirostris and Chinese black sleeper Bostrichthys sinensis live in the intertidal zone, but their feeding habits are different. The adult B. pectinirostris is herbivorous, whereas the adult B. sinensis is carnivorous; however, differences between the two species are not clear with regard to distribution patterns and activities of the intestinal enzymes. This study thus investigated the distribution patterns and specific activities of four disaccharidases (maltase, sucrase, lactase and trehalase), two proteases [leucine-amniopeptidase (LAP) and gamma-glutamyltranspeptidase (gamma-GT)] and an alkaline phosphatase (ALP) in brush border membrane fractions obtained from three purified intestinal sections of the two species. The highest activities of the four disaccharidases were found in the midgut of B. pectinirostris and in the foregut of B. sinensis. Highest activities of the two proteases and ALP occurred in the hindgut of B. pectinirostris and in the midgut of B. sinensis. The activities of the four disaccharidases in each intestinal section of B. pectinirostris were significantly (P < 0.05) higher than in those of B. sinensis. The levels of LAP, gamma-GT and ALP activities in the three intestinal sections varied in B. pectinirostris and B. sinensis, suggesting that the primary regions for disaccharide digestion were in the midgut in B. pectinirostris and in the foregut in B. sinensis, and that the hindgut of B. pectinirostris and the midgut of B. sinensis should play important roles in final protein digestion and nutrient absorption, respectively. The activities of the four disaccharidases in the two species were well correlated with their feeding habits. However, no clear-cut correlation between the activities of the two proteases and diet could be concluded from the present study.