|
type |
Journal Article |
authors |
Kobayashi J.; Shimizu, Y.; Mutaguchi, Y.; Doi, K.
|
title |
Characterization of d-amino acid aminotransferase from Lactobacillus salivarius |
journal |
J. Mol. Catal. B: Enzymatic |
Activity |
2.6.1.21 |
Family |
2.6.1.21 |
sel |
selected |
ui |
http://dx.doi.org/10.1016/j.molcatb.2013.04.013 |
year |
(2013) |
volume |
94 |
pages |
15–22 |
| |
keywords |
Alanine/metabolism/*pharmacology |
abstract |
We searched a UniProt database of lactic acid bacteria in an effort to identify d-amino acid metabolizing enzymes other than alanine racemase. We found a d-amino acid aminotransferase (d-AAT) homologous gene (UniProt ID: Q1WRM6) in the genome of Lactobacillus salivarius. The gene was then expressed in Escherichia coli, and its product exhibited transaminase activity between d-alanine and α-ketoglutarate. This is the first characterization of a d-AAT from a lactic acid bacterium. L. salivariusd-AAT is a homodimer that uses pyridoxal-5′-phosphate (PLP) as a cofactor; it contains 0.91 molecules of PLP per subunit. Maximum activity was seen at a temperature of 60 °C and a pH of 6.0. However, the enzyme lost no activity when incubated for 30 min at 30 °C and pH 5.5 to 9.5, and retained half its activity when incubated at pH 4.5 or 11.0 under the same conditions. Double reciprocal plots of the initial velocity and d-alanine concentrations in the presence of several fixed concentrations of α-ketoglutarate gave a series of parallel lines, which is consistent with a Ping-Pong mechanism. The Km values for d-alanine and α-ketoglutarate were 1.05 and 3.78 mM, respectively. With this enzyme, d-allo-isoleucine exhibited greater relative activity than d-alanine as the amino donor, while α-ketobutylate, glyoxylate and indole-3-pyruvate were all more preferable amino acceptors than α-ketoglutarate. The substrate specificity of L. salivariusd-AAT thus differs greatly from those of the other d-AATs so far reported. |
last changed |
2014/02/17 11:21 |
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