AFFECTING THE ACTIVITY OF SOYBEAN LIPOXYGENASE-1

The iron content in soybean lipoxygenase-1 is important for enzyme act ivity. If the iron is removed by a chelating agent, the activity of th e enzyme will decrease. The active center includes the iron ligands an d the surrounding environment, and any conformational change in the ac tive center may affect the activity of the enzyme. It is shown that th e activity of soybean lipoxygenase-1 is enhanced by chloride anion, ph osphate, formate, borate, etc., especially at a lower concentration of substrate. It is also shown that one of four thiols in soybean lipoxy genase-1 is accessible to DTNB at 0.1% SDS without losing great activi ty, 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 mercu ric cyanide without losing great activity. These results support the h ypothesis that only one, or possible two cysteines are responsible for the loss of activity. Two-substrate and two-product binding site mode ls are proposed here and discussed in view of high-resolution X-ray cr ystal structure. (C) 1996 by Elsevier Science Inc.