MOLECULAR-WEIGHT OF POLY(3-HYDROXYBUTYRATE) DURING BIOLOGICAL POLYMERIZATION IN ALCALIGENES-EUTROPHUS

Poly(3-hydroxybutyrate) [P(3HB)] was produced by Alcaligenes eutrophus from fructose or butyric acid in nitrogen-free media at different pHs and temperatures, and the time-dependent changes in the molecular weight of P(3HB) were studied. P(3HB) polymers were accumulated within cells in the presence of a carbon source, and the rate of P(3HB) accumulation increased with temperature in the 16-35 degrees C range but was almost independent of the pH value (5.0-8.0) of the media. The apparent activation energy for the rate of P(3HB) accumulation was 30 kJ/mol. The number-average molecular weight (($) over bar M(n)) of P(3HB) polymers increased rapidly with time during the course of P(3HB) accumulation to reach a maximum value ((10 +/- 2 x 10(5)) at around 6 hours of incubation, followed by a gradual decrease in ($) over bar M(n) with time. The polydispersities (($) over bar M(w)/($) over bar M(n)) of P(3HB) polymers increased from 1.5 to 2.0 during P(3HB) accumulation. The time-dependent changes in ($) over bar M(n) have been accounted for in terms of the kinetic model in which a chain transfer agent is formed during the course of P(3HB) synthesis and reacts with a growing chain of P(3HB) on the active site of polymerase to regulate the length of P(3HB) chain.