Functional characterization of alanine racemase from Schizosaccharomyces pombe: a eucaryotic counterpart to bacterial alanine racemase.
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.
Laboratory of Microbial Biochemistry, Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
T
T
Uo
T
T
Yoshimura
N
N
Tanaka
K
K
Takegawa
N
N
Esaki
D000409:Alanine / Q000378:metabolism; D000411:Alanine Racemase / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D012568:Schizosaccharomyces / Q000201:enzymology* / Q000254:growth & development
D000411:Alanine Racemase; D000409:Alanine