Auxins action on Glycine max secretory phospholipase A(2) is mediated by the interfacial properties imposed by the phytohormones

Secretory phospholipase A(2) (sPLA(2)) are soluble enzymes that catalyze the conversion of phospholipids to lysophospholipids and free fatty acids at membrane interfaces. The effect of IAA and IPA auxins over the activity of recombinant sPLA(2) isoforms from Glycine max was studied using membrane model systems including mixed micelles and Langmuir lipid monolayers. Both phytohormones stimulate the activity of both plant sPLA(2) using DLPC/Triton mixed micelles as substrate. To elucidate the mechanism of action of the phytohormones, we showed that both auxins are able to self-penetrate lipid monolayers and cause an increment in surface pressure and an expansion of lipid/phytohormone mixed interfaces. The stimulating effect of auxins over phospholipase A(2) activity was still present when using Langmuir mixed monolayers as organized substrate regardless of sPLA(2) source (plant or animal). All the data suggest that the stimulating effect of auxins over sPLA(2) is due to a more favorable interfacial environment rather to a direct effect over the enzyme. (C) 2015 Elsevier Ireland Ltd. All rights reserved.