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Computer Simulation of In Vitro Formation of PHB Granules: Particulate Polymerization
Author(s) -
Jurasek Lubo,
Nobes Geoffrey A. R.,
Marchessault Robert H.
Publication year - 2001
Publication title -
macromolecular bioscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.924
H-Index - 105
eISSN - 1616-5195
pISSN - 1616-5187
DOI - 10.1002/1616-5195(20010801)1:6<258::aid-mabi258>3.0.co;2-g
Subject(s) - granule (geology) , polymerization , coalescence (physics) , monomer , chemistry , chemical engineering , polymer , kinetics , dispersity , brownian dynamics , biophysics , polymer chemistry , materials science , brownian motion , organic chemistry , composite material , physics , quantum mechanics , astrobiology , engineering , biology
The kinetics of poly(3‐hydroxybutyrate) granules formed in vitro from [ R ]‐(–)‐3‐hydroxybutyryl–Coenzyme A (CoA) monomer in the presence of PHA synthase were followed using transmission electron microscopy (TEM) and Cryo‐TEM. Round granules were formed rapidly at the beginning of the experiment, growing from the initially observed diameter of 0.1 μm to about 1 μm within a few minutes. In contrast to the rapid granule growth, the initial conversion (polymerization) rate was slow. After a lag phase lasting several minutes, the conversion rate reached its maximum value while the total number of granules steadily declined. We account for these observations as follows: • The initial granules are vesicle‐like, being stabilized by a monomolecular enzyme layer on their surface. • The initial granules are microporous, i.e., contain some polymer but are mainly filled with water. • The granules collide due to Brownian motion and coalescence occurs accounting for most of the diameter growth. • The polymerization is topotactic and is hindered by the surface energy required to extrude the hydrophobic polymer into the largely aqueous environment inside the granules. • As the granules accumulate PHB, polymerization is increasingly favored and its rate reaches a maximum. A computer program was written to test the model. The dynamic display simulates the in vitro growth of the granules in three‐dimensional space. The simulation mimics granule formation, monomer conversion, Brownian motion, and coalescence. The sizes and compositions of all particles are recorded and simulated data are plotted and compared with experimental observations. The computer simulation approximated the experimental data and validated the mechanistic hypotheses.