Modulation of guanosine triphosphatase activity of G proteins by arachidonic acid in rat Leydig cell membranes

Previous results from our group have indicated that arachidonic acid decrease cAMP production through a modification of heterotrimericGproteins.\ud In the present study, we have characterized the high affinity GTPase activity present in Leydig cell membranes and its regulation by fatty acids. The high-affinity GTPase activity, measured as [g32P] GTP hydrolysis rate, was both time and protein concentration dependent. Arachidonic acid elicited a dose-dependent inhibition of enzyme activity with an IC50 5 26.7 6 1.1 mM. The existence of only two double bonds in linoleic acid is reflected by a decrease in its inhibitory activity (IC5053462.3mM). Saturated fatty\ud acids showed no effect at this level. The kinetic analysis as interpreted by Lineweaver-Burk plots, indicated that 50 mM arachidonic acid had no effect on the apparent affinity for GTP, but resulted in a 40% decreases in the maximal velocity of the reaction. Arachidonic acid modulation of GTPase activity was not attenuated by blocking eicosanoid metabolism with inhibitors of 59-lipoxygenase, cyclooxygenase, or epoxygenase P-450. The addition of arachidonic acid to pertussis toxin-treated membranes had no effect on the enzyme activity, indicating that arachidonic acid does not modify the GTPase activity present in Gas protein. However, ADP-ribosylation with cholera toxin followed by arachidonic acid treatment led to a further 40% inhibition\ud when compared with cholera toxin treatment alone. These results allowed us to postulate that arachidonic acid inhibits the GTPase activity of Gi protein family. To further analyze the mechanism of\ud arachidonic acid inhibition of GTPase activity, the effect of arachidonic acid on the [35S]GTPgS binding was studied. No effect of this fatty acid on GTP binding was found. Combining our previous results\ud with those found here, we can conclude that arachidonic acid maintains Gi proteins in their active state, which in turn inhibit adenylate cyclase and results in decrease cAMP levels

Antioxidant activity of twenty wild Spanish Thymus mastichina L. populations and its relation with their chemical composition

The antioxidant activity and chemical composition of essential oils and methanolic extracts of twenty Spanish Thymus mastichina L. populations were studied. Both essential oils and methanolic extracts possessed antioxidant properties. However, the total phenol contents of the methanolic extracts varied between 2.90 and 9.15mg GAE/g extract and the EC 25 values of DPPH free radical scavenging activity between 0.90 and 3.45mg/mL for the methanolic extracts and 78-241mg/mL for essential oils, these showing low antioxidant potential. Actually, in essential oils the main compound determined was the 1,8-cineole (56.8-69.6%), whereas thymol, γ-terpinene, terpinolene and geraniol (species with considerable DPPH scavenging activity) were observed in low amounts. Concerning methanolic extracts, rosmarinic acid was the most abundant polyphenol (1.70-9.85mg/g), followed by methoxysalicylic acid, apigenin, kaempferol and luteolin.The authors are grateful to the POCTEPePrograma Cooperação Transfronteiriça España-Portugal 2007 e 2013 for financial support through the project “Mejora de la competitividad del sector agrario de Castilla y León y Norte de Portugal a través de la innovación y el desarrollo de productos diferenciados de alto valor”.info:eu-repo/semantics/publishedVersio

Thymus masticina L. – Composição e bioactividade de exemplares com diferentes origens geográficas

O tomilho (Thymus sp.) e geralmente usado como especiaria e/ou erva medicinal com diversas propriedades farmacológicas, tais como anti-espasmódicas, anti-sépticas, anti-tússicas, expectorantes, entre outras. Os óleos essenciais extraídos do tomilho tem também encontrado uso na dieta humana, uma vez que tem sido demonstrada actividade antimicrobiana face a microrganismos patogénicos, tais como Staphylococcus aureus, Helicobacter pylori e Candida albicans