KINETICS AND MECHANISM OF SYNTHESIS AND DEGRADATION OF POLY(3-HYDROXYBUTYRATE) IN ALCALIGENES-EUTROPHUS

The kinetics and mechanism of the synthesis and degradation of poly(3-hydroxybutyrate) (P(3HB)) in Alcaligenes eutrophus have been studied. P(3HB) polymers were produced from fructose or butyric acid at 30-degrees-C and pH7.0 in a nitrogen-free mineral media. P(3HB)was accumulated in the cells while the carbon source was present in the media, and the accumulated P(3HB) was subsequently degraded after the carbon source was exhausted. The rates of P(3HB) accumulation were about 10 times higher than those of P(3HB) degradation. The number-average molecular weight (M(n)Bar) of P(3HB) polymers increased rapidly with time during P(3HB) accumulation to reach a maximum value after around 10 h of incubation, followed by a gradual decrease in M(n)BAR with time. The maximum values of M(n)BAR were in the range of 580 000-950 000, dependent upon the type and concentration of carbon source. The polydispersities (M(w)BAR/M(n)BAR) of P(3HB) polymers were almost constant at 2.0 +/- 0.3 during both P(3HB) accumulation and P(3HB)degradation. The number of P(3HB) polymer chains increased with time during P(3HB) accumulation, suggesting that a chain-transfer reaction of propagating chain takes place in this biological polymerization system. The number of P(3HB) polymerase molecules per cell was determined to be 18 000 from the time dependence of the number of P(3HB) polymer chains. A model of P(3HB) chain propagation and chain transfer on the active site of polymerase has been proposed together with a model of P(3HB) chain degradation on the active site of depolymerase.