Chemical modification of L-asparaginase with N, O-carboxymethyl chitosan and its effects on plasma half-life and other properties

<正> E.coli L-asparaginase,an antitumor enzyme,was chemically modified with N,O-carboxymethyl chitosan to lower its artigenicity and increase its plasma half-life.The results showed that the modified L-asparaginase has almost the same apparent Km value as that of native enzyme.The modified L-asparaginase also showed a higher protease stability against trypsin and a-chymotrypsin.After being modified,the enzyme exhibited the complete loss of antigenicity towards antiasparaginase serum.In addition,the higher the molecular weight of modifying reagents,the better the effects on reduction of antigenicity.When tested in vivo,the plasma half-life of the modified enzyme (t1/2=40 h) was over 33 times longer than that of the native enzyme (t1/2=1.2 h).

氮杂环改性壳聚糖-碘复合物的制备及抗菌活性

通过亲核加成-消除反应,壳聚糖与氮杂环吡啶醛形成亚胺结构,随后在静电引力作用下,与碘络合,制备氮杂环改性壳聚糖-碘复合物;采用紫外光谱、傅里叶变换红外光谱和X-射线衍射等对产物进行结构表征。所有结果证实,氮杂环改性壳聚糖-碘复合物已成功制备。体外抗菌结果显示,氮杂环改性壳聚糖-碘复合物对金黄色葡萄球菌和大肠杆菌的抑菌圈分别为(26.2±0.3)mm和(19.8±0.3)mm,具有较强的抗菌活性。因此,氮杂环改性壳聚糖-碘复合物有望开发为海洋生物医用抗菌敷料。

壳聚糖修饰L-天门冬酰胺酶对酶活及抗原的影响

采用水溶性壳聚糖对 L-天门冬酰胺酶进行化学修饰 ,修饰后的酶活回收率高达 70 % ,修饰酶的比活为每毫克蛋白质 1 2 1 .79U,p H值为 7.4,更接近于人体血浆 p H值 (7.2～ 7.4) ,对底物的亲和力有所提高 ,稳定性增加 ,抗原性仅为自然酶的 1 / 3 ,增加了临床使用的安全性。

壳聚糖的化学改性

研究了 N-酰化反应对壳聚糖溶解性能和结晶性能的影响以及反应时间 ,温度 ,配比对脱乙酰度的影响。

羧甲基壳聚糖结构与性质研究

由X-射线衍射证明壳聚糖在进行化学改性(羧甲基化)后,晶体结构已破坏,呈无定形结构,因而在任何pH范围内均溶于水。用元素分析法与红外光谱法测定羧甲基壳聚糖的取代度DS>1和脱乙酰化度为84%～92%,由此推断在C_2和C_6位上均有羧甲基取代,化学改性后的壳聚糖为N,O取代(即为N,O-CMC)。由凝胶过滤色谱测得N,O-CMC的分子量约为10~5～10~6,1%(W/V)的N,O-CMC溶液在50s^(-1)时的表观粘度为20mPa·s左右。