J. Biol. Chem., Vol. 262, Issue 18, 8648-8657, Jun, 1987
Structural studies on aspartate aminotransferase from Escherichia coli. Covalent structure
K Kondo, S Wakabayashi and H Kagamiyama
The amino acid sequence of aspartate aminotransferase from Escherichia coli
was established by sequence analysis and alignment of 39 tryptic peptides
and 7 cyanogen bromide peptides. The total number of amino acid residues of
the subunit was 396, and the molecular weight was calculated to be 43,573.
A comparison of the primary structure of the E. coli enzyme with all known
sequences of the two types of isoenzyme (mitochondrial and cytosolic
enzymes) in vertebrates revealed that approximately 25% of all residues are
invariant. The amino acid residues which were proposed from
crystallographic studies on the vertebrate enzymes to be essential for the
enzymic action are well conserved in the E. coli enzyme. The E. coli enzyme
shows a similar degree of sequence homology to both the mitochondrial and
cytosolic isoenzymes (close to 40%). The finding that the positions of
deletions introduced into the sequence of E. coli enzyme to give the
maximum homology agree well with those of the mitochondrial enzymes
supports the endosymbiotic hypothesis of mitochondrial origin.
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