| Krill belongs to Crustacea, which is widely distributing. The diet of krill contains large numbers of diatoms and copepods, and it locates at the primary phase of food cycle. Krill decomposes very soon by the efficient enzyme system, which can rapidly degrade protein and amylose.People have been paying much attention in Antarctic krill (Euphausia superbd). Antarctic krill is known to have a very efficient digestive system, which is based on a combination of enzymes controlled by inhibitors. The efficiency of these enzymes is clearly visualized when the krill post mortem is autolyzed, due to the disabling of the inhibitor system. The high proteolytic activity has raised a lot of interest and a number of studies on the characteristics of these enzymes have been performed. For example, krill enzymes have been shown to have a higher activity toward fibrin and casein compared to trypsin. Also, a serine proteinase from krill referred to as euphauserase has been sequenced, modified, and produced recombinantly. In the present work, proteinases refined from a krill extract used for an enzymatic debrider have been studied. The extract contains eight proteolytic enzymes: three trypsin-like serine proteinases, one chymotrypsin-like serine proteinase, two carboxypeptidase A enzymes, and two carboxypeptidase B enzymes. Krill enzymes are now being exploited for medical applications, such as debridement of necrotic wounds and removal of dental plaque.Euphausia pacifica is the dominant euphausiid species in the North Pacific. The present work is limited in ecology and distribution. We also find the krill post mortem can autolyzed. It can be explained there exists an inhibitor system in krill when it died, for the sake of the system disable, the proteinase degrade protein and amylose. Because of the amount of fishes reduced rapidly, and the krill, which is the diet of fish, rose accordingly. The krill is only used for aquaculture feed now, so studying the proteolytic enzymes will increase the additional value.In this thesis, the characteristics of Euphausia pacifica crude extract were investigated by different methods, which were used to purify and characterize the trypsin-like enzyme. By histochemistry method, we studied the digestive system and confirmed the site of trypsin-like enzyme in krill.Compared the two extracting buffer solution of 0.05mol/L Tris-HCl ( pH7.0) and distill water, we found the activity of proteolytic enzyme extracted from distill water is higher than that of Tris-HCl and-with good stability. Crude enzyme has high temperature stability. Keeping at constant temperature(20 ) for a longtime(30d), the activity remains more than 85%. After heat stimulation range from room temperature to 100 for 15min, the activity of crude enzyme reduced little while specific activity raised rapidly, that is to say, we can use simple method such as heat stimulation to get the proteolytic enzymes.Compared the depositions from 0%~50% (NH4)2SO4, The highest enzyme recovery rate obtained when the concentration of (NH4)2SO4 was 35%.The effect of pH on crude enzyme was examined. The major protein activity is at pH5.0 and a minor activity is at pH8~10. So it was implied that in crude enzyme there are both acid proteases and more than one kinds of alkaline proteases.It was found that trypsin-like enzyme isolated as monomeric protein had a molecular weight of 35 000Da.The enzyme activity was extremely sensitive to ovomucoid and Benzamidine, very sensitive to PMSF, TLCK, however not sensitive to TPCK, indicated that it belongs to the group of serine-type protease.In order to confirm the site of trypsin-like enzyme in Euphausia pacifica, we examined the digestive system by using histochemistry method. The digestive system of Euphausia pacifica mainly composed of digestion duct and gland. The digestion duct can be divided by gullet, stomach (cardia stomach and pylorus stomach), mid-gut and hindgut. Mid-gut gland is the main digestive gland. Observed by Olympus microscope, the structure of krill digestive...
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