Change of surface structure of poly(3-hydroxybutyrate) film upon enzymatic hydrolysis by PHB depolymerase.
Change of surface structure of poly(3-hydroxybutyrate) film upon enzymatic hydrolysis by PHB depolymerase.
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DOI：
10.1021/bm020077a
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发表时间：
2002-09
影响因子：
6.2
通讯作者：
N. Yoshie;Yoshihiro Oike;K. Kasuya;Y. Doi;Y. Inoue
中科院分区：
文献类型：
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作者：
N. Yoshie;Yoshihiro Oike;K. Kasuya;Y. Doi;Y. Inoue
采用衰减全反射红外光谱法（ATR/IR）分析了聚[(R)-3-羟基丁酸盐][PHB]膜在酶解过程中的表面结构变化。酶系为从皮氏Ralstonia pickkettii T1和假单胞菌stutzeri分离的PHB解聚合酶。通过ATR/IR光谱中羰基拉伸带的曲线分解，估计了含有0、1和4 μ g PHB解聚酶的缓冲液对PHB薄膜表面结晶度的影响。人们普遍认为，酶解首先发生在非晶相，然后在结晶相进行降解，细胞外PHB解聚合酶只能降解膜表层的聚合物链。因此，预计酶降解后表面结晶度会增加。然而，结果却与这一预期相反。酶的作用降低了表面结晶度。由于ATR/IR光谱法对样品表面分子结构的微小变化很敏感，因此ATR/IR实验显示的结晶度下降可能并不表明结晶相的规律性完全丧失。由于晶体表面的链比晶体内部的链更具流动性，因此在PHB的ATR/IR光谱中，晶体表面的C=O波段可能出现在与非晶相或界面相相似的位置。只有晶体内部的链才会形成结晶相的C=O带。因此，我们更倾向于认为ATR/IR光谱中结晶峰的下降反映了PHB薄膜表面层片的破裂引起的链迁移率的变化或晶体表面积的增加，或者两者兼而有之。
The change in the surface structure of poly[(R)-3-hydroxybutyrate] [PHB] films upon the enzymatic hydrolysis was analyzed by attenuated total reflection infrared [ATR/IR] spectrometry. As enzymes, PHB depolymerases isolated from Ralstonia pickettii T1 and Pseudomonas stutzeri were used. By curve decomposition of the carbonyl stretching band of ATR/IR spectra, the change in the surface crystallinity of PHB films by exposure to buffer containing 0, 1, and 4 microg of PHB depolymerases was estimated. It has been widely believed that the enzymatic hydrolysis first occurs in the amorphous phase, followed by the degradation in the crystalline phase, and extracellular PHB depolymerase can degrade only polymer chains in the surface layer of the film. Therefore, the surface crystallinity had been expected to increase upon the enzymatic degradation. However, the results were contrary to this expectation. The surface crystallinity was decreased by the enzymatic attack. Because ATR/IR spectrometry is sensitive to a small change in molecular structure of the sample surface, the decrease in the crystallinity shown by ATR/IR experiments probably does not indicate the complete loss of regularity of the crystalline phase. Because the chains at crystalline surface are more mobile than those inside the crystals, the C=O band for crystalline surface may appear at a position similar to those of the amorphous or interfacial phase in ATR/IR spectra of PHB. Only the chains inside the crystals may contribute to the C=O band of the crystalline phase. Thus, we rather suppose that the decrease in the crystalline peak of the ATR/IR spectra reflects the change in chain mobility or the increase of crystalline surface area by cracking of lamellas at the surface layers of PHB films or both.