Enzymatic Degradation and Adsorption on Solution-Grown Lamellar Crystals of Poly(β-propiolactone) with an Extracellular PHB Depolymerase

Abstract

Solution-grown lamellar crystals of poly(β-propiolactone) (PPL) were hydrolyzed by polyhydroxybutyrate(PHB) depolymerase from Alcaligenes faecalis T1. The enzymatic degradation process of the lath-shaped crystals was visualized by transmission electron microscopy and atomic force microscopy. The molecular weight change during enzymatic degradation was measured by gel permeation chromatography. The enzymatic degradation progressed from the edges of lath-shaped crystals to yield a serrated outline. Lamellar thickness and molecular weight of the crystals almost remained unchanged during the enzymatic hydrolysis. Furthermore, it was confirmed that the chain-folding structure on the crystal surface remained intact during degradation by polyethylene decoration method. Adsorption of enzyme molecules on crystal surface was observed using an immuno-gold labeling technique. Based on these results, it was concluded that the adsorption of enzymes occurs unselectively on the chain-folding surfaces, but the degradation occurs only from the edges. Comparison of the degradation and adsorption mechanism is made with the representative biodegradable polyester, poly[R]-3-hydroxybutyrate) lamellar crystals.