|
type |
Journal Article |
authors |
Uo, T.; Yoshimura, T.; Tanaka, N.; Takegawa, K.; Esaki, N. |
title |
Functional characterization of alanine racemase from Schizosaccharomyces pombe: a eucaryotic counterpart to bacterial alanine racemase |
journal |
J Bacteriol |
Activity |
5.1.1.1 |
Family |
5.1.1.1.a |
sel |
selected |
ui |
11244061 |
year |
(2001) |
volume |
183 |
number |
7 |
pages |
2226-33 |
| |
keywords |
Alanine/metabolism |
abstract |
Schizosaccharomyces pombe has an open reading frame, which we named alr1(+), encoding a putative protein similar to bacterial alanine racemase. We cloned the alr1(+) gene in Escherichia coli and purified the gene product (Alr1p), with an M(r) of 41,590, to homogeneity. Alr1p contains pyridoxal 5'-phosphate as a coenzyme and catalyzes the racemization of alanine with apparent K(m) and V(max) values as follows: for L-alanine, 5.0 mM and 670 micromol/min/mg, respectively, and for D-alanine, 2.4 mM and 350 micromol/min/mg, respectively. The enzyme is almost specific to alanine, but L-serine and L-2-aminobutyrate are racemized slowly at rates 3.7 and 0.37% of that of L-alanine, respectively. S. pombe uses D-alanine as a sole nitrogen source, but deletion of the alr1(+) gene resulted in retarded growth on the same medium. This indicates that S. pombe has catabolic pathways for both enantiomers of alanine and that the pathway for L-alanine coupled with racemization plays a major role in the catabolism of D-alanine. Saccharomyces cerevisiae differs markedly from S. pombe: S. cerevisiae uses L-alanine but not D-alanine as a sole nitrogen source. Moreover, D-alanine is toxic to S. cerevisiae. However, heterologous expression of the alr1(+) gene enabled S. cerevisiae to grow efficiently on D-alanine as a sole nitrogen source. The recombinant yeast was relieved from the toxicity of D-alanine. |
last changed |
2009/01/08 14:52 |
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