The catalytic efficiency of soybean lipoxygenase-1 is enhanced at low gravity

Several cellular processes are modified when cells are placed under conditi ons of weightlessness. As yet, there is no coherent explanation for these o bservations, nor it is known which biomolecules might act as gravity sensor s. Lipoxygenases generate leukotrienes and lipoxins from arachidonic acid, being responsible for many pharmacological and immunological effects, some of which are known to be affected by microgravity. In the course of the 28t h parabolic flight campaign of the European Space Agency we measured the ac tivity of pure soybean lipoxygenase-1 on linoleic acid, by a fibre optics s pectrometer developed on purpose. It was found that microgravity reduced th e apparent Michaelis-Menten constant (K-m) of the enzymatic reaction to one fourth with respect to the 1 g control, whereas, the catalytic constant (k (cat)) was unaffected. Consequently, the catalytic efficiency of lipoxygena se-1 (k(cat)/K-m) was approximately four-fold higher in flight than on grou nd. This unprecedented finding suggests that lipoxygenase-1 might be a mole cular target for gravity. (C) 2001 Elsevier Science B.V. All rights reserve d.