| Liu KewuAbstract: Sucrase was isolated and purified from small intestine of pig and its properties had also been examined. The sucrase was isolated by homogenate and purified by salting-out, chromatography with DEAE-Sepharose column and gel filtration with Sephacryl S-200 and Sephadex G-200. The purified enzyme moved as a single electrophoretic band in PAGE. The specific activity is 1.79 units/mg protein. Its subunit weight is 51000 daltons as determined with SDS-PAGE and its pi is 6.7 as determined with IEF. Amino acid composition analysis showed that the sucrase has about 477 amino acids and there are plentiful of Gly, Glu, Leu, Asp, Thr, Val and Pro in it. It was demonstrated that the enzyme has 28.8 % a-helix, 27.9% p-sheet, 43.2% random coil by the analysis of circular dichroism spectrum. Dynamic analysis showed that the optimum pH value for the enzyme is 6.9. The optimum temperature is about 50 癈 . The Michaelis-Menten constant (Km) is 18.9mmol/L on the sucrose. Thermal stability showed that the sucrase was stable under 40 癈. -SH was demonstrated to be essential functional groups of the enzyme by chemical modification. The effect of p-chloromercuri benzoate (PCMB) on sucrase is anticompetitive inhibition, and its Kj is 0.75mmol/L. Dithiothreitol (DTT) modification, NR/R one-dimensional SDS-PAGE and NR/R two-dimensional SDS-PAGE showed there is no disulfide bond in sucrase.Activity differences of the enzyme were determined when metal ions effected on the sucrase. The result showed that K+, Fe2+, Co2+, A13+ and Sb3"1" have no inhibition on sucrase activity. Zn2+, Mn2+, Mg2+ could activate the sucrase and Zn2+ was the strongest activator. Li\ Ni2+, Cu2+, Pb2+, Cd2+, Hg2+, Ag+, Cr3+ and EDTA could inhibit the sucrase and Ag"1" was the strongest inhibitor. In these metal ions, transition metal ions such as Ni2"1", Mn2"1", Co2"1", Cu2+ and Zn2+ could activate sucrase respectively at low concentration. The activation of Zn2+ was increased with the concentration increase. And the activity of sucrase increased to 140% when 5.0 mmol/L Zn2"1" was used. At the same concentration, the activation of Mn2"1", Co2+ didn't increased and Ni2"1" had a slight inhibition on the activity of sucrase. Cu2+ increased the activity of sucrase with the increase of Cu2+concentration below the certain level, and then appeared inhibition effects with the concentration increase above the level. When 1.0 mmol/L Cu + was used, the activity of sucrase increasedby 13.6%. The activity didn't change when 3.0 mmol/L Cu2+ was used, and that was decreased to 58.3% when 5mmol/L Cu2+ was adopted. The inhibition of sucrase by heavy metal ions such as Ag+, Hg2+ and Cd2+ could increase with their concentration increase. The activity of sucrase could be inhibited thoroughly by 5mmol/L of Ag+. And the inhibition has a linear increase with the EDTA concentration increase.Some Chinese traditional medicines (extract of 75% ethanol) were used to treat the sucrase. The result showed that RHIZOMA ATRACTYLODIS, RADIX PLATYCODONIS, CORTEX MORI, RHIZOMA ANEMORHEMAE, FRUCTUS SCHISANDRAE, RADIX OPHIPOGONIS, FOLIUM MORI, HERBA EPIMEDII, CORTEX MOUTAN, RHIZOMA ATRACTYLODIS MACROCEPHALAE, FRUCTUS MUME, RHIZOMA POLYGONATI, RADIX REHMANNIAE, FRUCTUS XANTHII, STYLUS ZEAE MAYDIS, SEMEN CUSCUTAE, RHIZOMA SCROPHULARIAE, RHIZOMA ALISMATIS and RHIZOMA POLYGOMATI OSORATI, totally 19 kinds of Chinese medicines, could inhibit the activity of sucrase. Among them, RHIZOMA ATRACTYLODIS, RADIX PLATYCODONIS and CORTEX MORI's inhibiton were stronger. When O.lml of 75% ethanol extract of RHIZOMA ATRACTYLODIS, RADIX PLATYCODONIS, CORTEX MORI were used, the activity of sucrase were decreased by 71.0%, 52.7% and 52.6% respectively. There were no effects when HERBA AGRIMONIAE, FRUCTUS LIGUSTRI LUCIDI, RADIX ASPARAGI, GYPSUM FIBROSUM, RADIX GINSENG and PORIA were used to react with sucrase. Pollen, CORTEX LYCII, RADIX REDGINSENG, RADIX ASTRAGALI, RADIX NOTOGINSENG, RHIZOMA DIOSCOREAE, RHIZOMA COPTIDIS and RADIX SALVIAE MILTIORRHIZAE showed positive effect on sucrase activity.
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