PURIFICATION AND CHARACTERIZATION OF THE POLY(HYDROXYALKANOIC ACID) SYNTHASE FROM CHROMATIUM-VINOSUM AND LOCALIZATION OF THE ENZYME AT THE SURFACE OF POLY(HYDROXYALKANOIC ACID) GRANULES

A recombinant strain of Escherichia coil, which overexpressed phaC and phaE from Chromatium vinosum, was used to isolate poly(3-hydroxyalkan oic acid) synthase. The isolation was performed by a two-step procedur e including chromatography on DEAE-Sephacel and Procion Blue H-ERD. Th e poly(3-hydroxyalkanoic acid) synthase consisted of two different kin ds of subunit (PhaC, M(r) 39500 and PhaE, M(r) 40500). PhaC was separa ted from the poly(3-hydroxyalkanoic acid) synthase complex by chromato graphy on phenyl-Sepharose; PhaE was enriched by solubilization of pro tein inclusion bodies. The stoichiometry of PhaC and PhaE in the enzym e complex was not determined. The poly(3-hydroxyalkanoic acid) synthas e (PhaEC) exhibited a native relative molecular mass of M(r) 400000 an d most probably consists of ten subunits. The K-m value of the enzyme for D(-)-3-hydroxybutyryl-CoA was 0.063 mM. The enzyme synthesized pol y(3-hydroxybutyric acid) in vitro from D(-)-3-hydroxybutyryl-CoA or, t ogether with propionyl-CoA transferase in a coupled enzyme reaction, s ynthesized the same product from acetyl-CoA plus D(-)-3-hydroxybutyric acid. Antibodies were raised against both subunits of the poly(3-hydr oxyalkanoic acid) synthase. By immunoelectron microscopy, the poly(3-h ydroxyalkanoic acid) synthase was localized within the cytoplasm in ce lls of C. vinosum grown under non-storage conditions. In cells grown u nder poly(3-hydroxybutyric acid) storage conditions, the enzyme was ob served to be located at the surface of the poly(3-hydroxybutyric acid) granules. Immunoblots with anti-PhaC, anti-PhaE IgG and crude extract proteins indicated that poly(3-hydroxyalkanoic acid) synthases with p artial sequence similarities are widespread among purple sulphur bacte ria.