Structural studies on the subunits of glutamate synthase from Azospirillum brasilense

The amino acid composition and the N-terminal sequences of the two dissimilar subunits of glutamate synthase from Azospirillum brasilense have been determined along with the sequences of selected CNBr peptides. Comparison of our data with those available for Escherichia coli glutamate synthase revealed an overall good homology between the enzymes from the two sources. This is more evident for the heavy subunits where the highly conserved N-terminal sequence containing Cys-1, suggests that this region may be involved in catalysis. However, it appears that the light subunits are different with respect to both their amino acid composition and their N-terminal region, suggesting that the latter may not be part of the enzyme active site. Finally, an extinction coefficient at 444 nm of 62.66 +/- 4.61 mM-1.cm-1 was determined.