Transferases in Polymer Chemistry - Enzymatic Polymerisation - page 25

acetyl-CoA molecules catalyzed by the -ketothiolase (PhaA), leading to the

formation of acetoacetyl-CoA, which is reduced to

β

( R ) -3-hydroxybutyryl-CoA

by the -3-Hydroxybutyryl-CoA

is substrate for the polyester synthase (PhaC) and the direct precursor of P3HB
biosynthesis [ 2 , 7 ]. In contrast to this, medium-chain-length PHAs are produced in
vivo from intermediates of fatty acid metabolism (see Fig. 3 ) .
PHAs can consist of a diverse set of repeating unit structures and have been stud-
ied intensely because the physical properties of these biopolyesters can be similar
to petrochemical-derived plastics such as polypropylene (see Table 1 ) . These bio-
logically produced polyesters have already found application as bulk commodity
plastics, fishing lines, and for medical use. PHAs have also attracted much atten-
tion as biodegradable polymers that can be produced from biorenewable resources.
Many excellent reviews on the in vivo or in vitro synthesis of PHAs and their prop-
erties and applications exist, underlining the importance of this class of polymers
[ 2 , 6 , 7 , 12 , 26 - 32 ] .
In the large-scale production of PHAs, the extraction and purification of PHA
from biomass is a crucial factor for determining the practical importance of these
polymers. It is important that PHAs can be extracted efficiently and easily, much
like the extraction of endogenous compounds such as starch, sucrose, and oil.

( R ) -specific acetoacetyl-CoA reductase (PhaB). ( R )

Tabl e 1 Comparison of the physical properties of the poly(3-/4-hydroxyalkanoate)s with poly-
propylene. With kind permission from Springer Science+Business Media [ 8 ]

Elongation at
break (%) T g ( ◦ C T m ( ◦ C Polyester ) ) Crystallinity References

P3HB 15 175 50-80 5 [ 9 ]

P3HV − 15, 0 110, 112, 118 56 [ 10 , 11 ]

−

P3HB- co -20mol%3HV 1 145 50 [ 12 ]

− 1

P3HB- co -10mol%3HHx 127 [ 13 ]

P3HB- co -17mol%3HHx − 2 120 850 [ 13 ]

P3HB- co -47mol%
3HV- co -16mol% 4HV-
co -15mol%3HHx- co -
2mol%3HO

− 15 118 1,000 [ 11 ]

P3MB 8 100 [ 14 ]

P4HB − 40 53 1,000 [ 10 ]

P(3HB- co -16%4HB) 43 444 [ 15 ]

P3HPE − 11 63 [ 16 , 17 ]

PHO − 36 59, 61 [ 18 - 20 ]

PHN − 39 , − 29 48, 54, 58

P3H6MN Not determined 65 [ 19 , 20 ]

PH-p5TV 17 95 [ 21 ]

PH6PHx 4 Not determined [ 22 ]

PH5PoxV 14 Not determined [ 23 ]

PH- p -nitroPV 28 Not determined [ 24 ]

PH8-pMPoxO 14 97 [ 25 ]

Polypropylene − 15 176 50 400 [ 12 ]

T g glass transition temperature, T m melting temperature