Affecting the activity of soybean lipoxygenase-1

The iron content in soybean lipoxygenase-1 is important for enzyme activity. If the iron is removed by a chelating agent, the activity of the enzyme will decrease. The active center includes the iron ligands and the surrounding environment, and any conformational change in the active center may affect the activity of the enzyme. It is shown that the activity of soybean lipoxygenase-1 is enhanced by chloride anion, phosphate, formate, borate, etc., especially at a lower concentration of substrate. It is also shown that one of four thiols in soybean lipoxygenase-1 is accessible to DTNB at 0.1% SDS without losing great activity, and that all four thiols are accessible to DTNB at 1% SDS and lose all activity. Two or three of the four thiols are accessible to mercuric cyanide without losing great activity. These results support the hypothesis that only one, or possibly two cysteines are responsible for the loss of activity. Two-substrate and two-product binding site models are proposed here and discussed in view of high-resolution X-ray crystal structure.