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。然而，还没有关于紫外线（UV）对蜘蛛丝的机械性能的影响的报道。我发现，紫外线机械地加强了在白天活动的棒形络新妇蜘蛛分泌的拖丝。与紫外线照射前相比，拉铲的机械强度在紫外线A照射下增加了约50%，在紫外线B照射下增加了约40%，在紫外线C照射下增加了约7%。机械强度强烈地取决于分子量。用ESR方法研究了紫外光照射诱导自由基的产生。自由基导致归因于蛋白质中的化学裂解的分子量降低，并且还导致归因于蛋白质分子之间的交联的分子量增加。因此，机械强度的最大值可能来自两个因素：归因于蛋白质分子中的化学裂解的机械强度的降低和归因于交联的产生的机械强度的增加。最后，研究结果表明，紫外线照射的机械强化的球网和延长重建的球网的时间。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.