The microbial polyesters have attracted attention as an biodegradable materials for a wide range of agricultural

marine and medical applications．It is important to investigate the biodegradation behavior and kinetics of the biodegradable reaction．Traditional Michaelis-Menten kinetics was originally derived for homogeneous reactions in which both the enzyme and the substrate are soluble．The enzymatic degradation of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) is a heterogeneous reaction

because PHBV is an insoluble substrate

and the kinetic relation needs to be altered to fit it．In this paper

the kinetics of the enzymatic degradation behavior of PHBV was studied．It is well known that the enzymatic hydrolysis of water-insoluble film of PHB by depolymerases produces water-soluble products composed of monomers and dimers of R-3-hydroxybutyric acid．The rates of degradation were determined by the titrimetric methods

which are quantitative by directly measuring the acid groups formed as a result of ester bend hydrolysis．The degradation of PHA samples with different shapes and morphology was studied．The kinetic analysis revealed that the degradation reaction exponentials of PHBV powder

solution-casting film and solution-casting-leaching porous film were different

which were inconsistent with classical enzymatic kinetics．The variations of kinetics curves depended on the concentration of enzyme and PHA．A heterogeneous kinetics treatment was derived to describe the relationship of degradation rates with enzyme concentrations and substrates．The influence of PHBV physical morphology on their degradation was also investigated．The results show that the specific surface area and the shape of PHA samples effect the adsorption and combination of enzyme to substrates and finally conduce to the changes of enzymatic degradation process and the rate of degradation of PHBV．