Regulation of plasma membrane Ca(2+)-ATPase activity by acetylated tubulin: influence of the lipid environment.

We demonstrated previously that acetylated tubulin inhibits plasma membrane Ca(2+)-ATPase (PMCA) activity in plasma membrane vesicles (PMVs) of rat brain through a reversible interaction. Dissociation of the PMCA/tubulin complex leads to restoration of ATPase activity. We now report that, when the enzyme is reconstituted in phosphatidylcholine vesicles containing acidic or neutral lipids, tubulin not only loses its inhibitory effect but is also capable of activating PMCA. This alteration of the PMCA-inhibitory effect of tubulin was dependent on concentrations of both lipids and tubulin. Tubulin (300µg/ml) in combination with acidic lipids at concentrations >10%, increased PMCA activity up to 27-fold. The neutral lipid diacylglycerol (DAG), in combination with 50µg/ml tubulin, increased PMCA activity >12-fold, whereas tubulin alone at high concentration (≥300µg/ml) produced only 80% increase. When DAG was generated in situ by phospholipase C incubation of PMVs pre-treated with exogenous tubulin, the inhibitory effect of tubulin on PMCA activity (ATP hydrolysis, and Ca(2+) transport within vesicles) was reversed. These findings indicate that PMCA is activated independently of surrounding lipid composition at low tubulin concentrations (<50µg/ml), whereas PMCA is activated mainly by reconstitution in acidic lipids at high tubulin concentrations. Regulation of PMCA activity by tubulin is thus dependent on both membrane lipid composition and tubulin concentration.

Control of Aspergillus section Flavi growth and aflatoxin accumulation by plant essential oils.

AIMS: The antifungal effect of Pimpinella anisum (anise), Pëumus boldus (boldus), Mentha piperita (peppermint), Origanum vulgare (oregano) and Minthosthachys verticillata (peperina) essential oils against Aspergillus section Flavi (two isolates of Aspergillus parasiticus and two isolates of Aspergillus flavus) was evaluated in maize meal extract agar at 0.982 and 0.955 water activities, at 25 degrees C. METHODS AND RESULTS: The percentage of germination, germ-tube elongation rate, growth rate and aflatoxin B(1) (AFB(1)) accumulation at different essential oils concentrations were evaluated. Anise and boldus essential oils were the most inhibitory at 500 mg kg(-1) to all growth parameters of the fungus. These essential oils inhibited the percentage of germination, germ-tube elongation rate and fungal growth. AFB(1) accumulation was completely inhibited by anise, boldus and oregano essential oils. Peperina and peppermint essential oils inhibited AFB(1) production by 85-90% in all concentrations assayed. CONCLUSIONS: Anise and boldus essential oils could be considered as effective fungitoxicans for Aspergillus section flavi. SIGNIFICANCE AND IMPACT OF THE STUDY: Our results suggest that these phytochemical compounds could be used alone or in conjunction with other substances to control the presence of aflatoxigenic fungi in stored maize.

Screening of Argentine plant extracts: impact on growth parameters and aflatoxin B1 accumulation by Aspergillus section Flavi.

The effect of essential oils, ethanolic and aqueous extract of 41 vegetable species on Aspergillus section Flavi growth was evaluated. The in vitro screen was a two-stage process. A wide-spectrum initial screen which identified promising antifungal plant extracts was carried out first. After that, identified extracts were studied in more detail by in vitro assays. A total of 96 plant extracts were screened. Essential oils were found to be the most effective extract controlling aflatoxigenic strains. Clove, mountain thyme, poleo and eucalyptus essential oils were selected to study their antifungal effect. Studies on percentage of germination, germ-tube elongation rate, growth rate, and aflatoxin B1 accumulation were carried out. Clove, mountain thyme and poleo essential oils showed the most antifungal effect under all growth parameters analyzed as well as aflatoxin B1 accumulation. Our results suggest that mountain thyme and poleo, which are native vegetal species of Argentina, and clove essential oils could be used alone or in conjunction with other substances to control the presence of aflatoxigenic fungi in stored maize.