Biosynthesis of polyesters from some unusual amino acids having linear carbon skeleton by Alcaligenes eutrophus

Abstract

AbstractThe biosynthesis of polyesters by Alcaligenes eutrophus from some unusual amino acids having a linear carbon skeleton was investigated. Poly(3‐hydroxybutyrate) (P(3 HB)) or poly(3‐hydroxy‐butyrate‐co‐3‐hydroxyvalerate) (P(3HB‐co‐3HV)) was found to be accumulated in the cells when a‐amino acids with a linear carbon skeleton were used as the sole carbon source. The 3HV mole fractions in copolyesters ranged up to 70%. The following pathway is proposed; the a‐amino acid with a linear carbon skeleton is at first metabolized to form the a‐keto acid by oxidative deamination with transaminase. Then the resulted a‐keto acid is converted into acyl‐CoA by oxidative decarboxylation, and the acyl‐CoA is further metabolized to the 3HB or 3HV unit through the same pathway as the fatty acids. P(3HB) was found to be produced from a‐amino acids having a linear skeleton with odd carbon number, whereas P(3HB‐co‐3HV) arises from a‐amino acids having a linear skeleton with even carbon number. This regularity is inverse to that of fatty acids, because amino acids are decarboxylated, with a reduction of one carbon atom, and then enter into the same synthetic pathway as fatty acids to form polyesters. On the other hand, when ω‐amino acids with a linear carbon skeleton were used as the sole carbon source, accumulation of polyesters was scarcely detected.