Two distinct forms of the chitin-degrading enzyme N-acetyl-beta-D-glucosaminidase in the Antarctic krill: specialists in digestion and moult

In the Antarctic krill Euphausia superba two forms of the chitinolytic enzy me N-acetyl-beta-D-glucosaminidase (NAGase, EC 3.2.1.52) have been describe d, previously identified as NAGase B and NAGase C. Here, we demonstrate the organ-specific distribution and physiological relevance of both forms usin g a polyclonal antibody preparation which allows them to be distinguished i mmunologically. While NAGase B was localized in the integument and displaye d a pattern of activity related to the moult cycle, the activity of NAGase C was independent of the moult cycle and was predominantly found in the gas trointestinal tract. Accordingly, NAGase B played a significant role in chi tin degradation during the krill's moult, whereas NAGase C participated in the digestion of chitin-containing dietary components. Chromatographic elut ion profiles of isolated organs confirmed the immunological results by disp laying characteristic organ-specific patterns in NAGase activity. The molec ular characteristics of the moulting form, NAGase B, may further indicate a vesicular transport of moulting enzymes from the epidermis into the ecdysi al space. Based on our results we develop a hypothesis explaining the concu rrent processes of simultaneous chitin degradation and chitin synthesis occ urring during moult.