Study on mechanism for mechanical strengthening of spider silks by ultraviolet rays as a new material.

近年来，许多研究人员将蜘蛛丝作为一种新材料进行了研究。然而，目前还没有关于紫外线对蜘蛛丝机械性能影响的报道。我发现紫外线机械地加强了在白天活动的Nephila clavata蜘蛛分泌的拖丝。即机械强度在紫外线照射后不久上升，达到最大值后逐渐下降。实际上，经过UV-A、UV-B和UV-C辐照后，拖丝的机械强度分别比辐照前提高了约50%、约40%和约7%。机械强度很大程度上取决于分子量。ESR法发现紫外辐射诱导自由基生成。自由基导致由于蛋白质的化学裂解而导致的分子量的减少，也导致由于蛋白质分子之间的交联而导致的分子量的增加。因此，机械强度的最大值可能来自两个因素：由于蛋白质分子的化学裂解而导致的机械强度的降低和由于交联的产生而导致的机械强度的增加。最后，研究结果表明，紫外光照射可以机械强化网网，延长网网重建周期。因此，蜘蛛有效地利用紫外线作为环境因素。

Recently, many researchers have focused on spider silks as a new material. However, there are no reports on effects of ultraviolet(UV) rays upon the mechanical properties of spider silks. I found that UV rays mechanically strengthened the draglines secreted from Nephila clavata spiders which were active in daytime. That is, the mechanical strength increased shortly after the UV-irradiation, reached a maximum and decreased gradually.Actually, the mechanical strength of draglines increased by ca.50 % for the irradiation of UV-A, by ca.40 % for the irradiation of UV-B and ca.7 % for the irradiation of UV-C, compared with the value before the UV-irradiation. The mechanical strength strongly depends on the molecular weight. It was found by ESR method that UV-irradiation induced radicals. The radicals lead to a decrease in the molecular weight ascribed to the chemical cleavage in protein and also to an increase in the molecular weight ascribed to the cross links between protein molecules. Thus, the maximum in the mechanical strength may come from the two factors of a decrease of mechanical strength ascribed to the chemical cleavage in protein molecules and of an increase of mechanical strength ascribed to the creation of cross links. Finally, the results suggest that UV-irradiation mechanically strengthens the orb-web and lengthens the period of rebuilding the orb-web. As a result, the spider utilizes UV rays effectively as an environmental factor.