| Turbot Scophthalmus maximus L. is a culture species naturally living in Europe. It is newly imported to China by Yellow Sea Fisheries Research Institute in 1992. Turbot is adapted to living in low temperature, enduring low oxygen and can breed in high density. Now the turbot culture becomes a new industry in our sea economy. In order to promote its culture in our country, it is very necessary to do some work on its basic research. In this study, the main digestive enzymes in turbot were fully discussed. Main proteases were purified and their characters were studied. The vitro coefficient of feed material by turbot alimentaiy tract homogenates was studied. Finally, partial or total replacement offish meal by soybean meal in diet for turbot and the dietary enzyme were researched.(1) The protein is digested mainly by stomach and foregut, and starch mainly by foregut and pylorus cecum, and fat mainly by gui. The optimum temperature and pH of protease in each digestive organ such as stomach, pylorus cecum, foregut, midgut, hindgut are 40癈 pH2.0, 40癈 pHS.O, 60癈 pH8.0,40癈 pH8.5, 60癈 pH8.0, And for the amylase are 40 pH6.5, 40 pHS.O 40 pH7.5, 50 pH7.0, 40 pH8.0, for the lipase are 40 pH7.5, 40 pH6.5,40 pH7.0,40 pH 7.5, 40 pH 7.5. Otherwise, the optimum pH of all digestive enzymes increases in low temperature. And the optimum of temperature decrease when the reaction time is longer.(2)The protease activity of turbot is increased continually in all growth phases, and the maximum activity increase occurs between 30-day old and 90-day old. The lipase activity is also increased along with the gro \vth and the difference between each phase is not very great. The amylase activity s increased in the parr phase and decreased after 180-day. The dominant enzyme i> protease in all growth phases, and 180-day phase is the turning point during the growth of turbot.(3)Within a water temperature range of 10 ~ 25 , the weight of digestive organs in percentage of body weight tends to decrease with the increase of temperature. Andthe quantity of enzyme protein secreted by each digestive organ also tends to decrease, and the enzyme protein in intestine decreased farthest. The total enzyme activity is increased firstly and then decrease with the increase of the water temperature. Among the digestive enzymes, the activity of protease is affected most significantly.(4)At salt concentration range of OM-0.5M, the activity of proteases in pylorus cecum and gut of turbot are activated when the salt concentration is increased. And the activity of stomach protease is activated in low salt concentration but inhibited in high salt concentration. The activity of lipase and amylase is also activated firstly and inhibited in high salt concentration. The activity of lipase is affected strongly and protease is least affected by salt. Most digestive enzymes of each digestive organ are activated in the salt concentration between 0.2M-0.3M.(5)The stomach protease^ pylorus cecum protease and gut protease I are purified by using ammonium sulfate precipitation, DEAE-Sepharose F.F. , Sephadex G-100 column and Sephacryl S -200 column chromatography. The purified enzymes exhibit a single band on SDS-polyacrolymide gel electrophoresis (SDS-PAGE). Their molecular weights are determined to be about 39900Dal, 66009Dal and 86776Dal respectively. The stomach protease is stable at pH ranging from 1.0-9.0 and below 40 癈. The optimum temperature and pH of enzyme are 40 癈 and pH2.0 for stomach protease, 30-40癈 and pH9.0 for pylorus cecum protease , 50 癈 and pH8.5 for gut protease I . The stomach protease is activated by Mn2+, Cu2+, and inactivated by Fe3+, PMSF, TPCK, Pepstatin, PCMB. The pylorus cecum protease is activated by Mn2+, Mg2+ and inhibited by Cu2+, Zn2+, PCMB, TLCK. The gut protease I is activated by Mn2+ and inhibited by Cu2+, Zn2+, Ag+, Fe3+, PCMB and TLCK. The Km value of stomach protease and gut protease I are determined to be 2.55g/L and 2.92g/L respectively.(6) The vitro dry matter digestive ability of each digestive organ is in the seq...
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