Chitobiase activity in the epidermis and hepatopancreas of the fiddler crab Uca pugilator during the molting cycle

The activity of chitobiase, also known as N-acetyl-beta-glucosaminidase, in the epidermis and hepatopancreas of the fiddler crab Uca pugilator (Bosc, 1802), during the molting cycle, was investigated. A pH optimum of 5 to 6 w as found for the enzymatic activity in both the epidermis and hepatopancrea s. The temperature optimum for epidermal and hepatopancreatic chitobiase ac tivities was 50 to 60 degrees C. The K-m values for epidermal and hepatopan creatic chitobiase activities at 19 degrees C were 0.190 +/- 0.027 and 0.20 3 +/- 0.016 mM 4-methylumbelliferyl-N-acetyl-beta-glucosaminide respectivel y. Hepatopancreatic chitobiase activity was significantly higher than epide rmal enzymatic activity in all the molt cycle stages tested except Postmolt Stage A-B. Chitobiase activity Varied significantly during the molting cyc le, with the epidermal enzymatic activity in Premolt Stage D3-4 significant ly higher than in Stage C (intermolt) and Premolt Stage D-0, whereas hepato pancreatic chitobiase activity in Premolt Stage D3-4 Was significantly high er than in all other molt stages tested. The patterns of chitobiase activit y in the epidermis and hepatopancreas correlate well with the hemolymph tit er of ecdysteroids in U. pugilator during the molting cycle; this suggests that chitobiase activity in both tissues is regulated at least in part by t he steroid molting hormones.