Splintering of poly(3-hydroxybutyrate) single crystals by PHB-depolymerase a from Pseudomonas lemoignei
Splintering of poly(3-hydroxybutyrate) single crystals by PHB-depolymerase a from Pseudomonas lemoignei
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DOI：
10.1021/ma961219u
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发表时间：
1996-12-16
期刊：
影响因子：
5.5
通讯作者：
Jendrossek, D
中科院分区：
文献类型：
--
作者：
Nobes, GAR;Marchessault, RH;Jendrossek, D
为了进一步了解解聚合酶的作用机制，利用假单胞菌的pwb -解聚合酶A对折叠链片层单晶进行了部分降解。通过透射电镜观察细菌聚（3-羟基丁酸酯）（PHB）的酶降解单晶，发现其分裂平行于其长轴。降解前，晶体呈片层状，宏观尺寸约为2.5 μ m × 20 μ m，记录了细菌PHB的经典基面单晶衍射图。通过透射电镜观察，部分降解的晶体纵向破碎，呈针状形态。PHB的针状碎片仍然产生相同的晶体基面衍射图样。这些结果支持了PHB单晶降解的“边缘攻击”模型，并在分子水平上进行了解释。由于链折叠方向与晶体长轴平行，在降解过程中分子量没有下降。该机制解释了PHB球晶片向针状形态的转化，并表明PHB解聚合酶a具有内端和外端活性。
With the aim of improved understanding of the mechanism of depolymerase action, folded chain lamellar single crystals were partially degraded with PWB-depolymerase A from Pseudomonas lemoignei. Enzymatically degraded single crystals of bacterial poly(3-hydroxybutyrate), PHB, were observed by transmission electron microscopy and were found to be splintered parallel to their long axes. Prior to degradation, the crystals were lamellar with macroscopic dimensions of approximately 2.5 mu m by 20 mu m and the classical baseplane single crystal diffraction pattern corresponding to bacterial PHB was recorded. When observed by TEM, the partially degraded crystals had been splintered longitudinally, to a needlelike morphology. The needlelike fragments of PHB still yielded the same crystalline baseplane diffraction pattern. These results support an ''edge attack'' model for the degradation of PHB single crystals and explain, at a molecular level. the lack of decrease in molecular weight during the degradation since the direction of chain folding is parallel to the long axis of the crystals. The proposed mechanism explains the conversion of PHB spherulite lamellae into a needlelike morphology and suggests that PHB-depolymerase A has both endo and exo activity.