Exendin-4螺旋结构对生物活性及稳定性的影响

针对Exendin-4的螺旋结构特点, 采用去掉螺旋序列、 用3个连续Ala替换螺旋以及Gln13替换为Tyr13的方式对N端α-螺旋及C端α-螺旋进行改造, 设计出4个结构模拟物. 通过圆二光谱和荧光光谱进行结构分析, 结合模拟物生物活性实验, 分析Exendin-4螺旋结构与生物活性的关系. 结果表明：  Exendin-4的N端螺旋比C端螺旋对生物活性影响更大； 在抗二肽基肽酶（DPPⅣ酶）的稳定性实验中, C端螺旋比N端螺旋具有更好维系Exendin-4稳定性的作用； 螺旋结构中Tyr13可作为提高Exendin-4生物活性的重要优化位点.

MCNP Simulation of Shielding Effectiveness of New Type 3D Alloy

Monte Carlo program was used to simulate the shielding effectiveness of different adulterants and massfraction of adulterant for a X-ray spectrum at low energy. The simulation results show that the alloy shielding effectiveness has a positive correlation with atomic number of adulterant, and a positive correlation （ΔZ>0） or a negative correlation（ΔZ<0） with mass fraction of adulterant. With the increases of the absolute value ΔZ, the variation of shielding effectiveness is getting lager, and the variation range has a positive correlation with mass fraction of adulterant. The shielding effectiveness of TaW alloyis the best and is nearly not affected by the variation of mass fraction of adulterant. The transmission rate of different low energy X-ray obtained by MCNP simulation shows good agreement with the experimental value.