Antonio Rodolfo Sampietro

Comparison of the free radical-scavenging activity of propolis from several regions of Argentina

Propolis is extensively used in Argentine folk medicine. Alcoholic extracts of propolis from different regions of Argentina were prepared. The extracts were analysed for the determination of total flavonoid content (from 13.3 to 42.6 mg/g of propolis) by using the aluminum nitrate method, UV spectrophotometry and thin layer chromatography. All of them contained high total flavonoid content. It was also observed that all samples of ethanolic extracts of propolis showed free radical-scavenging activity in terms of scavenging of the radical DPPH but the highest activities were found for samples from Tucumán and Santiago del Estero. In all cases with 20 microg/ml of soluble principles, the percentage of DPPH degradation was different (Banda Oeste: 67.5%; Verónica: 45%; Forres: 35%; Saenz Peña: 20% and Juan José Castelli: 55%). These results may justify their use as a source of natural antioxidants.

Screening antifungal activities of selected medicinal plants

Plants synthesise a vast array of secondary metabolites that are gaining importance for their biotechnological applications. The antifungal activity of the ethanolic extracts of ten Argentinean plants used in native medicine is reported. Antifungal assays included radial growth inhibition, disk and well diffusion assays and growth inhibition by broth dilution tests. The chosen test fungi were yeasts, microfungi and wood-rot causing Basidiomycetes. Extracts of Larrea divaricata, Zuccagnia punctata and Larrea cuneifolia displayed remarkable activity in the assays against the majority of the test fungi. In addition to the former plants, Prosopanche americana also inhibited yeast growth.

Antioxidant activity of Argentine propolis extracts

Propolis is used in Argentine folk medicine. We have examined its possible protective action against oxidative modification of lipid in unfractionated serum. The kinetics of copper-induced oxidation was continuously monitored by measuring the formation of conjugated dienes, as the increase in the absorbance at 234 nm. According to the kinetics of oxidation, the propolis were classified in three different groups. Group I (CE, CO, BO, MO, BE) inhibited lipid oxidation during the initiation and propagation phases even at low concentrations. Group II (SP, CA, AM) increased the lag-phase for conjugated diene formation. All propolis in groups I and II diminished the maximal rate of diene production and the maximal amount of dienes produced. Group III (PA, RA, FE, VR, TV) had no effect on the lipid oxidation. The extent of lipoprotein oxidation was measured by the thiobarbituric acid reactive substance assay. Generation of malondialdehyde-like substances was inhibited and delayed by the presence of propolis extracts from group I and II. Our results justify the use of propolis (groups I and II) as a source of natural antioxidants.

Screening of antibacterial activity of Amaicha del Valle (Tucumán, Argentina) propolis

Propolis is extensively used in Argentine folk medicine. Alcoholic extracts of propolis from four localities of Amaicha del Valle (El Paraiso, La Banda Este, La Banda Oeste and El Molino), Province of Tucumán and from Cerrillos, Province of Santiago del Estero, Argentina were prepared. All showed antibacterial activity against Gram positive bacteria, the propolis from La Banda Este being the most active (MIC = 7.8 microg/ml) against Streptococcus piogenes, an antibiotic resistant bacterium. Thin layer chromatographic (TLC) separation profiles of propolis from Amaicha del Valle region were similar but differ from the alcoholic extract of the propolis from Cerrillos, another phytogeographical region of Argentina (provincia chaqueña). Bioautographic assays of the TLC profiles showed that several separated compounds of the Amaicha del Valle propolis have antibacterial activity. The difference in composition between Amaicha del Valle and Cerrillos propolis coincides with a different phytogeographical formation.

A regulatory invertase from sugar cane leaf-sheaths.

Abstract A soluble β-fructofuranosidase was isolated from sugar cane leaf-sheaths. The enzyme attacks sucrose with an activation energy of 5700 cal/mol above 30° and 17 000 cal/mol below 30°. The enzyme was inhibited by the reaction products. Glucose is a simple non-competitive inhibitor, but fructose is a competitive inhibitor. Kinetic studies using double reciprocal plots and replots of 1/K i , slope vs inhibitor concentration showed that fructose binds to two interacting sites of the enzyme. Per cent residual activity plotted against inhibitor concentration, and Hill plots confirmed the regulatory properties of the invertase. n was found to be close to 2, the number of binding sites established with the double reciprocal method. The tissue and cellular levels of sucrose, fructose and glucose were measured. Fructose was found at inhibitory concentrations confirming that the activity of the enzyme is probably modulated by the hexose pool of the leaf-sheaths.

Localization of invertase activities in ricinus communis leaves

Leaf tissue from Ricinus communis possesses cell wall and soluble invertases. These activities may be distinguished on the basis of their optimum pH and Km and the action of various inhibitors. Ca 84% of the soluble invertase was found in vacuolar preparations.

Hydrolysis of sucrose within isolated vacuoles from Solanum tuberosum L. tubers

Abstract. The soluble acid invertase (β-D-fructofuranoside fructohydrolase, EC 3.2.1.26) from potato (Solanum tuberosum L. cv. Kennebec) tubers was located in the vacuoles. Although the functionality of this invertase in the vacuoles has been assumed, the activity of the enzyme has never been shown within isolated vacuoles. Vacuoles were prepared by gentle osmotic shock from free protoplasts obtained by enzymic digestion of tuber tissues. The mean volume of these vacuoles, (0.26 ± 0.05) × 10−2 μl, was estimated by optical microscopy. Sucrose, glucose and fructose concentrations were calculated to be 100 mM, 20 mM and 40 mM, respectively, in the vacuoles. Sucrose hydrolysis and the increase in glucose and fructose concentrations within the vacuoles were measured during vacuolar incubations. An almost identical pattern of sucrose hydrolysis by invertase was found by an in-vitro assay reproducing the vacuolar conditions. In view of the determinations of internal vacuolar pH (5.2), the possibility of spontaneous hydrolysis of sucrose was disregarded. Vacuoles were shown to be free from proteinaceous inhibitors, confirming the extravacuolar location of these inhibitors. The vacuolar hydrolytic pattern of sucrose confirms the regulatory role of the reaction products previously proposed for in-vitro assays.

Modulation of potato invertase activity by fructose

Abstract The invertase from Solanum tuberosum is inhibited by its reaction products, fructose and glucose. The inhibition by fructose fits well with a case of inhibition through two interacting sites ( K i 0.18 M, α K i 0.33 M). This inhibition is not suppressed by proteins as occurs with invertases inhibited in a simple way by their reaction products. Thus fructose could be an important effector, in vivo , of this enzyme. Glucose is a non-competitive classical inhibitor ( K i 1.02 M) whose inhibitory action is not suppressed by proteins.

Partial purification and properties of invertase from Carica papaya fruits

Abstract The invertase (EC 3.2.1.26) from Carica papaya fruits was isolated and partially purified. The enzyme exhibits simple Michaelis-Menten kinetics and the Km is 4.2 ±0.02 × 10−3M. The optimum pH is 4.5. The enzyme is inhibited by fructose but not by glucose. The inhibition by fructose fits well with a case of inhibition through two interacting sites. Inhibition by fructose is not suppressed by proteins as occurs with other plant invertases. According to these results fructose appears to be an important effector of this enzyme.

Purification and characterization of the invertase from Pycnoporus sanguineus

A constitutive invertase (EC 3.2.1.26) was isolated and purified by the first time from Pycnoporus sanguineus. The enzyme is a glycoprotein. Its relative molecular mass is about 84,000 and its structure is dimeric, with two identical subunits (about 41,000). The enzyme is able to attack sucrose, raffinose, stachyose, inulin and levan, being sucrose the preferred substrate (Km 4.89 +/- 0.13 mM). Fructose was a classical competitive inhibitor, but glucose was not an inhibitor of the enzyme. Lectins with specificity toward glucose are inhibitors of the enzyme. Glucose was present in invertase acid hydrolysates. Unlike higher plant invertases, bovine serum albumin is not an effector of the Pycnoporus sanguineus enzyme, and the inhibition by fructose is not suppressed by this protein. The properties of the Pycnoporus sanguineus enzyme are discussed with reference to higher plant invertases.