The relevance of the structure of lysine bound to Sepharose for the affinity of rabbit plasminogen
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The features of the structure of lysine, linked to Sepharose by the alpha-amino group, which are important for affinity chromatography of rabbit plasminogem were studied. Nine lysine and lysine-like conjugates, including epsilon-aminohexanoic acid DL-norleucine, DL-alpha-aminoadipic acid, DL-alpha-epsilon-diaminopimelic acid, cadaverine L-ornithine, L-arginine and D-lysine, were prepared; Using labelled rabbit plasminogen added to plasma, the ability of each conjugate to absorb plasminogen and separate the allomeric forms, type I and type II, during epsilon-aminohexanoic acid gradient elution was compared to Sepharose-L-lysine. Plasminogen had no affinity for Sepharose-epsilon-aminohexanoic acid, and was only weakly attracted by Sepharose-norleucine, Sepharose-cadaverine and others. Sepharose-ornithine held a greater attraction to the protein but the strongest binding was obtained with Sepharose-arginine. The affinity of plasminogen type I was always less than type II for the Sepharose-lysine analogues and the recovery of type II greater than type I from Sepharose-ornithine and Sepharose-arginine. Plasminogen affinity was in the order of Sepharose-arginine greater than Sepharose-lysine greater than Sepharose-ornithine. However, because of the present difficulty in recovering plasminogen from Sepharose-arginine the use of Sepharose-lysine in the affinity chromatography of rabbit plasminogen remains unchallenged. It is concluded that binding of rabbit plasminogen to conjugates of lysine and its analogues is determined by the presence of both a free carboxyl and a free amino group and that the distance between these groups is critical.
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