Gar. Nobes et al., SPLINTERING OF POLY(3-HYDROXYBUTYRATE) SINGLE-CRYSTALS BY PHB-DEPOLYMERASE-A FROM PSEUDOMONAS-LEMOIGNEI, Macromolecules, 29(26), 1996, pp. 8330-8333
With the aim of improved understanding of the mechanism of depolymeras
e action, folded chain lamellar single crystals were partially degrade
d with PWB-depolymerase A from Pseudomonas lemoignei. Enzymatically de
graded single crystals of bacterial poly(3-hydroxybutyrate), PHB, were
observed by transmission electron microscopy and were found to be spl
intered parallel to their long axes. Prior to degradation, the crystal
s were lamellar with macroscopic dimensions of approximately 2.5 mu m
by 20 mu m and the classical baseplane single crystal diffraction patt
ern corresponding to bacterial PHB was recorded. When observed by TEM,
the partially degraded crystals had been splintered longitudinally, t
o a needlelike morphology. The needlelike fragments of PHB still yield
ed the same crystalline baseplane diffraction pattern. These results s
upport an ''edge attack'' model for the degradation of PHB single crys
tals and explain, at a molecular level. the lack of decrease in molecu
lar 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 m
orphology and suggests that PHB-depolymerase A has both endo and exo a
ctivity.