Potato (Solanum tuberosum var. Desiree) tuber 5-lipoxygenase selectivity for the physicochemical properties of linoleic acid.

摘要

The dependence of 5-lipoxygenase (LOX) activity from potato cv. Desiree tubers on the physicochemical properties of linoleic acid (LA) was studied using pH and beta-cyclodextrin (beta-CD) as tools to investigate the effect of the physicochemical state of LA on LOX kinetic properties in vitro. The LA concentration dependence of LOX activity was best described by using the Hill equation. It was observed that the decrease of LOX activity at high pH corresponded to a pKa lower than the pKa of LA, and such a decrease was assigned to some ionizable side chain group of LOX related to the active centre. At a fixed LA concentration, the presence of beta-CD resulted in a decrease in the LOX reaction rate due to its effect on K and the Hill constant. Vmax was unaffected. Experiments in the presence of beta-CD revealed that LA monomers were also used as substrate, although less efficiently than aggregates. It is suggested that the different activities exhibited against monomers and aggregates may explain theobserved apparent substrate cooperativity, which may be interpreted as an aggregate-induced enzyme activation. The effect of beta-CD on LOX activity could be explained on the basis of the specific interaction between LA and beta-CD and the equations derived for such interaction developed in a previous work.