Synthesis and degradation of polyhydroxyalkanoates in Alcaligenes eutrophus

Abstract

The kinetics and mechanism of the synthesis and degradation of polyhydroxyalkanoates (PHA) in Alcaligenes eutrophus have been studied. PHA polymers were accumulated in the cells in nitrogen-free mineral media containing various carbon substrates, and the accumulated PHA polymers were subsequently degraded after the carbon sources were exhausted. The number of PHA polymerase molecules per cell was determined to be 18,000. The kinetic data of poly(3-hydroxybutyrate) (P(3HB)) synthesis indicated that about two molecules of d(−)-3-hydroxybutyryl-CoA are added within 1 s into a propagating chain of P(3HB) on the active site of polymerase, and that the average lifetime of a propagating P(3HB) chain is about 1 h. The intracellular PHA depolymerase was suggested to be exo-type hydrolase. The pathway and regulation of PHA synthesis were studied using [5- 13C]pentanoic acid as the sole carbon source.