Direct Observation of Enzymatic Degradation Behavior of Poly[(R)-3-hydroxybutyrate] Lamellar Single Crystals by Atomic Force Microscopy

Abstract

The enzymatic degradation behavior of solution-grown single crystals of poly[(R)-3-hydroxybutyrate] (P(3HB)), which were adsorbed on the surface of highly ordered pyrolytic graphite, with an extracellular PHB depolymerase from Alcaligenes faecalis T1 was directly observed by atomic force microscopy. At the initial stage of degradation, enzymatic action of both adsorption and hydrolysis produced smaller crystal blocks by predominant degradation of distorted regions of a single crystal. Subsequently, the hydrolysis progressed from a generated end of the crystal block, resulting in the formation of cracks. The degradation also took place at a middle part of the crystal, yielding slits. Several cracks and slits stood in a line along the long axis of crystal, and further enzymatic hydrolysis combined the cracks and the slits into longer cracks. With these processes, the enzymatic degradation converted a lath-shaped lamellar single crystal into lathlike fingers and crystal fragments. It has been proposed from t...