| 摘要 |
Methods are provided for producing block copolymers of PHAs in biological systems by controlling the sequence distribution in PHA copolymers. The method of controlling the sequence distribution preferably is achieved by (1) modulating the profile of substrate feeding; and/or (2) controlling the enzyme activities which supply the activated monomer. The biological systems include PHA-producing organisms that contain PHA synthase and metabolic pathways for the snythesis of two or more different activated monomers, i.e, hydroxyalkanoyl-CoA esters. In the preferred method, a block copolymer is produced via fermentation by microorganisms wherein one or more genes which encode proteins responsible for PHA chain cleavage termination, or transfer process are inactivated or encode inactive proteins, using the sequential and separate feeding of different substrates, wherein each substrate is fed until the desired extent of polymerization has been achieved, and then depleted or removed from the medium. In an alternative embodiment, block copolymers of PHA are produced in a recombinant, PHA-producing plant, wherein the sequence distribution is selectively varied by controlling the enzyme activities which supply the activated monomer.
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