Industrial Biotransformations

l-Aspartase
Escherichia coli
1) Reaction conditions
[1]: 1 M, 150.14 g · L –1 [150.14 g · mol –1 ] (ammonium fumarate)
pH: 8.5
T: 37 °C
medium: aqueous
reaction type: C-N bond cleavage
catalyst: immobilized whole cells
enzyme: l-aspartate ammonia-lyase (fumaric aminase, aspartase)
strain: Escherichia coli B ATCC 11303
CAS (enzyme): [9027–30–9]
2) Remarks
● l-Aspartic acid is produced batchwise via fermentation or enzymatic synthesis since 1953.
● The stability of isolated and immobilized aspartase is not satisfactory. Therefore the cells are
immobilized on polyacrylamide or, preferably, on κ-carrageenan.
● This process is the first example of the application of immobilized whole cells.
● It is one of the rare examples where the synthesis of an amino acid via an enzymatic route is
economically more attractive than the usual fermentation methods.
● The costs of the process are reduced to two thirds in comparison to batchwise operation.
● The activity of the cells is increased 10-fold by immobilization.
EC 4.3.1.1
1 = fumaric acid
2 = aspartic acid Tanabe Seiyaku Co., Ltd.
Fig. 4.3.1.1 – 1
HOOC
COOH
E
+ NH 3
HOOC
1 L-2
COOH
● The half-life of the cells is about 12 days. By addition of about 1 mM Mg 2+ ,Mn 2+ or Ca 2+ it can
be increased to more than 120 days.
● A heat exchanger (multiple, small isothermic pipes) is used, because the reaction is exothermic.
The use of a fixed bed reactor is advantageous.
● The product is isolated by titration to the isoelectric point (pH 2.8) with H 2SO 4 and filtration of
the precipitate.
● This synthesis step is often combined with the synthesis of l-alanine in a two step biotransformation
starting from fumaric acid (see page 451).
500
NH 2