KINETIC AND STRUCTURAL STUDIES ON THERMAL INACTIVATION OF LIPOXYGENASE L1 - EFFECT OF NONIONIC SURFACTANTS

Lipoxygenase 1 (LOX1) from soybean was irreversibly inactivated at 54 degrees C at pK 9.0, the midpoint of the thermal inactivation temperat ure (T-m) being 44+/-1 degrees C. The kinetics of thermal inactivation of the enzyme followed the first-order kinetics with an estimated rat e constant of 1.5x10(-4) s(-1) and a half-life of 36 min at 42 degrees C. The irreversible inactivation of the enzyme involved the oxidation of cysteine residues resulting in the intermolecular cross-linking. H owever, the conformation of the enzyme molecule remained practically u naltered. The nonionic surfactants Brij 35 and Tween 20 enhanced the t hermal stability. The enhanced thermal stability could be due to stren gthening of hydrophobic interactions around the cysteine residues.