HETEROGENEOUS KINETICS OF THE ENZYMATIC DEGRADATION OF POLY(BETA-HYDROXYALKANOATES)

The kinetics of the enzymatic degradation reactions of the naturally p roduced polyesters poly(beta-hydroxybutyrate) (PHB) and poly(beta-hydr oxybutyrate-co-beta-hydroxyvalerate (PHBV) by appropriate depolymerase s were studied. Specially, the interaction between the extracellular P HB depolymerase of Pseudomonas lemoignei and both PHB powder and solut ion-cast films of PHBV was investigated. Kinetic analysis of titristat ically and turbidimetrically determined rates of degradation has revea led that the observed degradation behaviour was inconsistent with clas sical Michaelis-Menten enzymatic kinetics. Depending upon the relative concentrations of enzyme and substrate, each exhibited a range of kin etic dependencies from zero order to first order. At high relative con centrations of enzyme, the reaction rate became inversely proportional to enzyme concentration. A new kinetic treatment was derived which pr edicted the observed variations in kinetic dependence on both enzyme a nd substrate, and it successfully described previously published kinet ic data for this and other PHB depolymerases. The degradation of PHB b y the PHB depolymerase of Aspergillus fumigatus M2A was investigated f or comparison. While the specific rate constants of this enzyme differ ed from that of P. lemoignei, the general kinetic model was still appl icable. (C) 1997 Elsevier Science Ltd.