type	Journal Article
authors	Hosono, A.; Mizuguchi, H.; Hayashi, H.; Goto, M.; Miyahara, I.; Hirotsu, K.; Kagamiyama, H.
title	Glutamine:phenylpyruvate aminotransferase from an extremely thermophilic bacterium, Thermus thermophilus HB8
journal	J Biochem (Tokyo)
Activity	2.6.1.7
Family	2.6.1.7
sel	selected
ui	14769873
year	(2003)
volume	134
number	6
pages	843-51
keywords	Bacteria
abstract	A subfamily I aminotransferase gene homologue containing an open reading frame encoding 381 amino acid residues (M(r) = 42,271) has been identified in the process of the genome project of an extremely thermophilic bacterium, Thermus thermophilus HB8. Alignment of the predicted amino acid sequence using FASTA shows that this protein is a member of aminotransferase subfamily Igamma. The protein shows around 40% identity with both T. thermophilus aspartate aminotransferase [EC 2.6.1.1] and mammalian glutamine:phenylpyruvate aminotransferase [EC 2.6.1.64]. The recombinant protein expressed in Escherichia coli is a homodimer with a subunit molecular weight of 42,000, has one pyridoxal 5'-phosphate per subunit, and is highly active toward glutamine, methionine, aromatic amino acids, and corresponding keto acids, but has no preference for alanine and dicarboxylic amino acids. These substrate specificities are similar to those described for mammalian glutamine: phenylpyruvate aminotransferase. This is the first enzyme reported so far that has the glutamine aminotransferase activity in non-eukaryotic cells. As the presence of aromatic amino acid:2-oxoglutarate aminotransferase [EC 2.6.1.57] has not been reported in T. thermophilus, this enzyme is expected to catalyze the last transamination step of phenylalanine and tyrosine biosynthesis. It may also be involved in the methionine regeneration pathway associated with polyamine biosynthesis. The enzyme shows a strikingly high pK(a) value (9.3) of the coenzyme Schiff base in comparison with other subfamily I aminotransferases. The origin of this unique pK(a) value and the substrate specificity is discussed based on the previous crystallographic data of T. thermophilus and E. coli aspartate aminotransferases.
last changed	2009/04/15 12:10