= Solution
The compound <imidazole> resembles the metal-coordinating part of the <histidine> side chain and competes for binding to the <nickel> sites in <immobilized metal affinity chromatography>. At the lower concentration in the wash, it helps displace weakly or non-specifically bound <proteins> while the multiple contacts of the <histidine tag> retain the desired <enzyme>. At the higher elution concentration, competition is strong enough to displace the tagged <enzyme>. \b[Low <imidazole> improves washing; high <imidazole> elutes the target.] Remove or match the elution-buffer components before interpreting downstream assays, and verify purity independently of total <protein> concentration.
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