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Enzymatic Hydrolysis of Thioester Linkages in Bacterial Poly(3-hydroxybutyrate- co -3-mercaptopropionate)s by Poly(3-hydroxybutyrate) Depolymerase Isolated from Ralstonia pickettii T1

Comparative Study of Effects of Thio/Oxo Ester Linkages on Thermal Properties of Bacterial Poly[3-hydroxybutyrate- co -3-(mercapto/hydroxy)propionate]s

The enzymatic hydrolysis behavior of compositionally well-fractionated bacterial poly(3-hydroxybutyrate- co -3-hydroxyvalerate) [P(3HB- co -3HV)] with 3HV-unit content from 8 to 98 mol% and bacterial poly(3-hydroxybutyrate) [P(3HB)] has been investigated in the presence of poly(3-hydroxyalkanoate) depolymerases isolated from Ralstonia pickettii T1 and Acidovorax sp. TP4. The water-soluble degradation products were characterized by HPLC and 1 H NMR spectroscopy. P(3HB- co -3HV)s with the whole range of 3HV-unit content can be degraded by R. pickettii T1 depolymerase, while only P(3HB- co -3HV)s with 3HV-unit content less than 80 mol% can be degraded by Acidovorax sp. TP4 depolymerase. It was found that the enzymatic degradation behavior of fractionated P(3HB- co -3HV)s was affected not only by the comonomer unit composition and its distribution but also by the solid-state structure of P(3HB- co -3HV)s and further by the bacterial source of depolymerases. Based on the results, the mechanism of enzymatic degradation was discussed.

The comonomer-unit compositions and their distribution of as-produced bacterial copolyesters, including poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxy-butyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) are described in this paper. Each copolyester sample can be comonomer-unit compositionally fractionated into several fractions, indicating that the original copolymers are mixtures of copolymers with different comonomer-unit compositions. The effects of comonomer-unit compositional distribution on thermal properties, crystallization, biodegradability and solid-state phase behavior are investigated using comonomer compositionally fractionated copolymers.

Lidan Feng, Takumi Watanabe, Yong He, Yi Wang, Tomoyasu Kichise, Takeshi Fukuchi, Guo-Qiang Chen, Yoshiharu Doi, Yoshio Inoue* 1 Department of Biomolecular Engineering, Tokyo Institute of Technology, Nagatsuta 4259, Midori-ku, Yokohama 226-8501, Japan Fax: (þ81)45-924-5827; E-mail: yinoue@bio.titech.ac.jp 2 Polymer Chemistry Laboratory, RIKEN Institute, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan 3 Takasago Research Laboratories, Kaneka Corporation, Takasago, Hyogo 678-8688, Japan 4 Department of Biological Science & Biotechnology, Tsinghua University, Beijing 100084, China

The comonomer-unit compositional distributions have been investigated for bacterial poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HH)] samples with 3HH unit content of 13.8, 18.0, 22.0, and 54.0 mol %. They were comonomer compositionally fractionated using chloroform/n-heptane mixed solvent at ambient temperature. The fractionation of P(3HB-co-18.0 mol %3HH) and P(3HB-co-22.0 mol % 3HH), which could not be carried out effectively at room temperature, were refractionated at 70 degrees C in the mixed solvent. Fractions with different 3HH unit content in a wide range (from 4.4 to 80.7 mol %) were obtained. By use of these fractions with narrow compositional distribution, the comonomer composition dependence of thermal properties was investigated by differential scanning calorimetry. The melting point (T(m)) and heat of fusion (DeltaH) decreased as the 3HH unit content increased in the range of low 3HH content (40 mol %), while they increased as the 3HH unit content increased in the high 3HH content range (70 mol %). The minimum T(m) and DeltaH values were found to exist at 3HH unit content of about 60 mol %. The glass transition temperature (T(g)) decreased linearly with the increase of 3HH unit content. The values of T(m), DeltaH, and T(g) of P(3HB-co-3HH)s were compared with those of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxypropionate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and the effects of comonomer types on the thermal properties were revealed.