engleski

Binding of auxin-amino acid conjugates to serum albumin

The plant auxin, indole-3-acetic acid, also arises in bacterial, animal, and human metabolism and, in all these organisms, amino acid conjugates are its common metabolites. Their interaction with human serum albumin (HSA) is of interest 1. as a base for chromatographic separation methods, 2. as a readily available model helping to comprehend the interaction of auxin conjugates with plant proteins which are difficult to access, 3. as a step towards better understanding of auxin pharmacodynamics in humans, which is required because free auxins are promising experimental cancer therapeutics, but their clinical application can only be considered if the adverse effects of long-term exposure can be circumvented. Ligand-binding to HSA was investigated by high-pressure liquid chromatography (HPLC) using a column in which this protein was immobilized on a silica gel support. IAA, its higher homologues, indole-3-propionic acid and indole-3-butyric acid, and its conjugates with 11 protein amino acids and 10 of their isomers were tested. All these compounds had larger retention times than KNO3 which is eluted with the void volume. This proves their general affinity to HSA. Retention times were dependent on the distance between the acidic head group and the center of the lipophilic residue. When this was kept constant, there was an obvious correlation with overall lipophilicity as estimated from chromatographic properties on a column of C18-coated silica gel and by computational methods. In some cases, the HSA column separated IAA conjugates with L-amino acids from their isomers containing the corresponding D-amino acid moieties.

auxin-amino acid conjugate; IAA; IPA; IBA; immobilized human serum albumin; HSA; ligand binding; structure-affinity relationship

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