Improvement of lipoxygenase inhibition by octapeptides

The β-casein-derived octapeptide RINKKIEK is a noncompetitive inhibitor of soybean lipoxygenase (LOX). To investigate the molecular determinants for the enzyme–peptide interaction, a peptide library containing substitutional analogs of RINKKIEK was prepared by SPOT synthesis and analyzed for interaction with fluorescent-labeled LOX. The positively charged amino acid residues in RINKKIEK appear to be essential for the LOX–peptide interaction. Replacement of the negatively charged glutamic acid by any other amino acid residue improves LOX binding. For both RINKKIPK and RINKKISK this increase in LOX binding is accompanied by a threefold increase in LOX inhibition.