Transferases in Polymer Chemistry - Enzymatic Polymerisation - page 46

a b

IDI

OPP OPP

DMAPP

IPP

Organic phase

IPP IDS

OPP

OPP

Geranyl Diphosphate

Aqueous phase

IDS

IPP

OPP

OPP

OPP

IDS

Farnesyl Diphosphate IPP

OPP

IPP

OPP

IDS

IPP

DMAPP

OPP

IPP

IDI

OPP

OPP

IPP

OPP

Geranylgeranyl Diphosphate

IPP

n x IPP

OPP
n

trans -Polyprnyl Diphosphate

Fig. 13 Synthesis of polyisoprenyl diphosphates. ( a ) Biosynthetic pathway in archaea. ( b ) Con-
cept of the organic-aqueous dual-phase system. The light -and dark-shaded areas indicate the
aqueous and organic phases, respectively. Double-headed and single-headed arrows indicate iso-
merization by IDI and consecutive condensation by IDS, respectively. Reprinted from [ 271 ], with
permission from Elsevier

and IPP [ 270 ] . The higher the ratio of primer to substrate, the shorter the chains.
Thus, it is likely that the granule and its associated proteins in conjunction with
the elongation protein(s) will play a critical role in chain length control and will be
different from in vitro studies.
Recently Fujiwara et al. reported on the in vitro polymerization of trans -
polyisoprene using the enzymes isopentenyl diphosphate isomerase (IDI) and
trans -isoprenyl diphosphate synthase (IDS) [ 271 ] . IDI catalyzes the interconversion
of IPP and DMAPP. IDS can now catalyze the polymerization of IPP from DMAPP
as outlined above for the synthesis of natural rubber, and as outlined in Fig. 13 a .
However, the condensation process is inhibited due to hydrophobic interaction be-
tween IDS and hydrocarbon of the longer products. The hydrophobic chain of the
elongating product does not readily protrude into the aqueous phase and it tends
to interact with the enzyme. To achieve an efficient in vitro synthesis, the authors
used an organic-aqueous two-liquid phase system to successfully synthesize (low
molecular weight) trans -polyisoprene (see Fig. 13 b ).

5 Conclusions

It is obvious that transferases are powerful catalysts for the enzymatic synthesis of
interesting polymer systems such as polyesters, polysaccharides, and polyisoprenes.
Considering the range of reactions that transferases can in principle catalyze, it can