Kameda Tsunenori, Tamada Yasushi
National Institute of Agrobiological Sciences, 1-2 Ohwashi, Tsukuba 305-8634, Japan.
Int J Biol Macromol. 2009 Jan 1;44(1):64-9. doi: 10.1016/j.ijbiomac.2008.10.004. Epub 2008 Oct 22.
To elucidate the native-state crystal structure of beeswax from the Japanese bee, Apis cerana japonica, we determined the relationship between temperature and the 13C solid-state nuclear magnetic resonance (NMR) chemical shift of methylene carbon of beeswax, with comparison to n-alkanes and polyethylene in the orthorhombic, monoclinic, or triclinic crystal form. Variable-temperature 13C solid-state NMR observations of n-alkanes and polyethylene revealed that the chemical shifts of methylene carbon in the orthorhombic crystal form increased linearly with increasing temperature, that of the triclinic form decreased, and that of the monoclinic form was unaltered. These relations were compared with results of variable-temperature 13C solid-state NMR observation of beeswax. Results clarified that the two crystal forms comprising the beeswax in the native state are orthorhombic and monoclinic. The variable-temperature 13C solid-state NMR observations were also applied to interpret the differential scanning calorimetry (DSC) curve of beeswax. They were used to clarify the structural changes of beeswax for widely various temperatures. For beeswax secreted by the Japanese bee, the transition from the orthorhombic form to the rotator phase occurred at 36 degrees C, that is from the crystalline to the intermediate state at 45 degrees C. Moreover, the variable-temperature 13C solid-state NMR spectrum of honeybee silk in the native state was observed. Results demonstrated that the secondary structures of honeybee silk proteins in the native state comprised coexisting alpha-helix and beta-sheet conformations and that the amount of alpha-helices was greater. The alpha-helix content of honeybee silk was compared with that of hornet silk produced by Vespa larvae.
为了阐明日本蜜蜂（Apis cerana japonica）所产蜂蜡的天然态晶体结构，我们测定了蜂蜡亚甲基碳的温度与13C固态核磁共振（NMR）化学位移之间的关系，并与正交晶系、单斜晶系或三斜晶系晶体形式的正构烷烃和聚乙烯进行了比较。对正构烷烃和聚乙烯进行变温13C固态NMR观测发现，正交晶系晶体形式中亚甲基碳的化学位移随温度升高呈线性增加，三斜晶系的化学位移减小，单斜晶系的化学位移不变。将这些关系与蜂蜡的变温13C固态NMR观测结果进行了比较。结果表明，天然态蜂蜡包含的两种晶体形式为正交晶系和单斜晶系。变温13C固态NMR观测还被用于解释蜂蜡的差示扫描量热法（DSC）曲线。它们被用来阐明蜂蜡在广泛不同温度下的结构变化。对于日本蜜蜂分泌的蜂蜡，从正交晶系形式到旋转相的转变发生在36℃，即从结晶态到中间态发生在45℃。此外，还观测了天然态蜜蜂丝的变温13C固态NMR谱。结果表明，天然态蜜蜂丝蛋白的二级结构包含共存的α-螺旋和β-折叠构象，且α-螺旋的含量更高。将蜜蜂丝的α-螺旋含量与黄蜂幼虫所产黄蜂丝的α-螺旋含量进行了比较。
