<
FONT SIZE="-1">D-Amino acid oxidase (DAAO) was used to study the oxidative deamination o
f racemic mixtureso
f D,
L-methionine in its soluble and immobilized
forms and thus obtain the corresponding
![](/images/gi<font color=)
fchars/alpha.gi
f" BORDER=0>-ketoacid. The soluble enzyme
form was obtained
from a
Trigonopsis variabilis CBS 4095 extract,
free o
f L-amino acid oxidase, and was co-immobilized with a 200-
fold excess o
f catalase toavoid the undesirable side reaction o
f H
2O
2 with the
![](/images/gi<font color=)
fchars/alpha.gi
f" BORDER=0>-keto acid, which would otherwise renderits corresponding decarboxylated acid, the 3-methylthiopropionic acid (MTPA). With thisbiocatalyst, quantitative conversion (>98%) o
f D-methionine into the
![](/images/gi<font color=)
fchars/alpha.gi
f" BORDER=0>-keto acid 4-methylthio-2-oxobutyric acid (MTOB) and into MTPA was achieved using 5 mg·mL
-1 o
f biocatalyst at pH8.0, 25
![](/images/entities/deg.gi<font color=)
f">C, and pure oxygen at 3 vvm. A stirred tank reactor with in situ product removal(STR-ISPR) was developed to avoid conversion o
f MTOB into MTPA. The reaction mediumwas re-circulated through a strong anion exchange column (Amberlite IRA-400). This resultedin the complete removal o
f MTOB
from the reaction medium. A
fter the reaction, the reactionproducts were eluted sequentially with water (
L-methionine), 10 mM HCl (MTPA), and 0.5 MHCl (MTOB). A
fter elution, MTOB was crystallized to its sodium salt.