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In this study,a new affinity medium was prepared and applied for the purification of Angiotensin converting enzyme inhibitory peptides (ACEI).ACEI is usefull in treating hypertension,and many have been derived from food production protein by enzymatic hydrolysis[1].The compersition of protein hydrolysates is very complex,this is led to the need of rapid purification technology[2].Affinity is one of the most extensively used method for protein purification,due to its high selectivity,high resolution,and high capacity[3].With this technology,magnetic carriers are used as the support material and they can be easily separated from the medium by applying a magnetic field[4].Firstly,The magnetic agarose microspheres were prepared by the water/oil (W/O) emulsion technique with the size of 10.36ìm,the magnetic material Fe3O4 used in the magnetic microspheres was synthesised by coprecipitation of FeCl2 and FeCl3 in ammonia solution and treated under hydrothermal conditions.Secondly,the magnetic microsphere surface was actived by epichlorohydrin(ECH).Finally,the angiotensin converting enzyme(ACE) was immobilized on the ECH-functionalized microspheres and the immobilized ACE activity was 0.065U/g.The ACE-immobilized magnetic agarose microspheres were applied for purification of ACEI from the <5 kDa water-soluble extract of Saurida elongata hydrolysates that had been obtained by treatment with neutral protease.The ACE binding peptides were eluted by 1M NaCl.ACEI adsorption experiments were investigated under different conditions(i.e.,protein concentration,medium pH,NaCl concentration ).The adsorption capacity of ACE-immobilized magnetic agarose microspheres was 29.50 mg/g under the optimum condition.Repeated use 4 times,the adsorption capacity reduced to 8.03mg/ml.The elution was further purified by reverse-phase HPLC.Most of the fractions showed to have the ACE inhibitory activity in vitro and a ACEI structure was identified by Time-of-flight mass spectrometry analysis.The result showed that magnetic agarose microspheres can be used as an affinity medium to saperete ACEI as a first step and shorten the process greatly.