Purification of aspartase and aspartokinase-homoserine dehydrogenase I from Escherichia coli by dye-ligand chromatography

Improved purification schemes are reported for the enzymes l-aspartase and aspartokinase-homoserine dehydrogenase I from Escherichia coli. Dye-ligand chromatography on commercially available dye matrices are incorporated as key steps in these purifications. Red A-agarose has a high affinity for l-aspartase, which is then eluted as a homogeneous protein fraction with 1 m m l-aspartic acid. Green A-agarose shows a high binding affinity for the bifunctional enzyme aspartokinase-homoserine dehydrogenase I. Purification is accomplished by elution with NADP +, followed by formation of a ternary complex with NADP and cysteine, a good competitive inhibitor of the homoserine dehydrogenase activity, and rechromatography on Green A-agarose. The final specific activity of each purified enzyme equaled or exceed previously reported values, the overall yield of enzymes obtained was significantly higher, and these improved purification schemes were found to be more amenable to being scaled up for the production of large quantities of purified enzyme.