School of Biotechnology & Bioengineering and Institute of Bioscience and Biotechnology, Kangwon National University, 192-1, Hyoja 2-Dong, Chunchon 200-701, Kangwon-do, Republic of Korea.
Int J Biol Macromol. 2010 Dec 1;47(5):635-9. doi: 10.1016/j.ijbiomac.2010.08.010. Epub 2010 Aug 20.
pH-sensitive liposomes were prepared by modifying the surface of egg phosphatidylcholine (EPC) liposomes with hydrophobically modified silk fibroin (HmSF). For the hydrophobic modification of SF, palmitic acid residues were covalently attached to SF through amide bond. According to the result of TNBS assay, about 90% of amino groups of SF participated in the conjugation reaction with palmitic acid N-hydroxysuccinimide ester, and the number of palmitic acid residue per SF molecule was calculated to be 15.3. The fluorescence quenching of calcein in liposomal suspension decreased from about 80-50%, when the ratio of HmSF to phospholipid increased from 1:20 to 1:5. The maximum degree of release from liposomes incorporating HmSF (of which HmSF to phospholipid ratio was 1:20) for 5 min was about 95% at pH 4.5, 25% at pH 5.0, and 5% at pH 5.5, and no appreciable amount of release was observed in the range of pH 6.5 to pH 8.0. Under acidic conditions, HmSF is likely to perturb the packing of phospholipid in liposomal membrane, possibly due to the unionization of the carboxylic groups of the silk protein.
pH 敏感脂质体是通过用疏水改性丝素蛋白（HmSF）修饰卵磷酯（EPC）脂质体的表面制备的。为了对 SF 进行疏水改性，通过酰胺键将棕榈酸残基共价连接到 SF 上。根据 TNBS 分析的结果，SF 中的约 90%的氨基参与了与棕榈酸 N-羟基琥珀酰亚胺酯的共轭反应，并且计算出 SF 分子上的棕榈酸残基数为 15.3。当 HmSF 与磷脂的比例从 1:20 增加到 1:5 时，脂质体悬浮液中钙黄绿素的荧光猝灭从约 80%降低到 50%。在 pH4.5 时，包含 HmSF（其中 HmSF 与磷脂的比例为 1:20）的脂质体在 5 分钟内的最大释放程度约为 95%，在 pH5.0 时为 25%，在 pH5.5 时为 5%，在 pH6.5 至 pH8.0 范围内没有观察到明显的释放。在酸性条件下，HmSF 可能会扰乱脂质体膜中磷脂的堆积，这可能是由于丝蛋白的羧酸基团的离解。
