. Serum-and glucocorticoid-regulated kinase Sgk1 inhibits insulin-dependent activation of phosphomannomutase 2 in transfected COS-7 cells. Am J Physiol Cell Physiol 288: C148 -C155, 2005. First published September 1, 2004; doi:10.1152/ ajpcell.00284.2004.-Serum-and glucocorticoid-regulated kinase (Sgk1) is considered to be an essential convergence point for peptide and steroid regulation of ENaC-mediated sodium transport. We tried to identify molecular partners of Sgk1 by yeast two-hybrid screening. Yeast two-hybrid screening showed a specific interaction between Sgk1 and phosphomannomutase (PMM)2, the latter of which is an enzyme involved in the regulation of glycoprotein biosynthesis. The interaction was confirmed in intact cells by coimmunoprecipitation and colocalization detected using confocal microscopy. We were then able to demonstrate that Sgk1 phosphorylated PMM2 in an in vitro assay. In addition, we found that the enzymatic activity of PMM2 is upregulated by insulin treatment and that Sgk1 completely inhibits PMM2 activity both in the absence and in the presence of insulin stimulation. These data provide evidence suggesting that Sgk1 may modulate insulin action on the cotranslational glycosylation of glycoproteins.Sgk; protein glycosylation; CDGIa SGK1 IS A SERINE THREONINE KINASE (22) that regulates sodium absorption by the amiloride-sensitive sodium channel in kidney principal cells (1, 11). The kinase is activated by serum, steroids, insulin, and cAMP (6,14). Recent evidence suggests that serum-and glucocorticoid-regulated kinase (Sgk1) is an important molecular target that integrates the multiple endocrine inputs regulating sodium transport (2, 3). Studies with stably transfected A6 cell lines, a well-characterized model of the principal cells of the distal nephron, have demonstrated that the activation of the kinase is required for basal as well as hormone-stimulated sodium transport. The results are compatible with a model in which Sgk1, once activated by hormonal stimulation, interacts with molecules that mediate Sgk1 action on the epithelial sodium channel (ENaC). One of the classic tools with which to search for an interaction between molecules is based on the possibility of studying the expression of reporter genes in yeast two-hybrid systems (4). This method was recently used by Maiyar et al. (8) and allowed the identification of importin-␣ as an Sgk1-interacting protein, leading nuclear localization of Sgk1.Because our main interest was focused on Sgk1 regulation of sodium absorption in kidney cells, we decided to perform yeast two-hybrid screening using a kidney library as a source of prey cDNA.We found several clones coding for putative Sgk1-interactive molecules. One of them contained the full sequence of phosphomannomutase (PMM)2, a key enzyme regulating the early steps of protein glycosylation and responsible for autosomal recessive congenital disorders of glycosylation type Ia (CDGIa) (19).We present evidence based on colocalization and coimmunoprecipitation experiments that the int...

A fraction of a three-component system is defined as a thermodynamic entity that groups two components. In this work, the thermodynamics of fractions is developed. The Kern-Weisbrod method has been proposed for two-component systems, but by considering the system as fractionalized, this method can also be employed to calculate the specific partial quantities of the components of a three-component system. This method is used to study the swelling process of functionalized polymeric particles. A series of copolymers of butyl acrylate (BuA) and methyl methacrylate (MMA) functionalized with 0, 5, 10, 15, and 20 wt % of acrylic acid (AA) was synthesized by emulsion polymerization. A thermodynamic study of the polymeric particle swelling as a function of the acrylic acid content and the temperature was carried out. Specific partial volumes, compressibilities, and expansibilities were calculated using density and speed of sound measurements. It was found that the hydration behavior of carboxylic and nonpolar groups of the polymeric particles is thermodynamically driven in accordance with the Gibbs-Duhem equation.

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Chia (Salvia hispanica L.) seeds contain antioxidants with great benefits for health and are widely used in the food industry. Antioxidants can be degraded by environmental factors, decreasing their biological activity. Their encapsulation in chitosan (CH) particles represents an alternative to protect them and increases their application. The encapsulation efficiency (%EE) of the antioxidants in the CH particles depends on the synthesis conditions. In this study, two methods for encapsulation of chia extract in chitosan particles were evaluated: method A, 0.05% CH in 1% acetic acid was mixed with 0.07% of tripolyphosphate (TPP) and method B, 0.3% CH in 2% acetic acid was mixed with 1% TPP. The results showed that the %EE decreased with the concentration of the extract, and the FTIR analysis suggested that the compounds of the extract were adsorbed on the surface of the particles. Dynamic light scattering and zeta potential analysis showed that the particles of method A are unstable and with a tendency to agglomerate, and the particles of method B are stable. The highest %EE was obtained with 0.2 mg·mL−1 (method A) and 1.0 mg·mL−1 (method B) of the extract. The higher loading capacity (%LC) (16–72%) was exhibited by the particles of method A. The best particle yield (62–69%) was observed for method B. The particles with the extract adsorbed showed antioxidant activity (5–60%) at 25°C; however, in the particles with the extract encapsulated, the activity increased after subjecting to acidic conditions at 40°C due to the breakdown of the particles. The results obtained will allow choosing the appropriate conditions for the synthesis of chitosan particles loaded with chia extracts with specific characteristics (%EE, %LC, size, and type) according to their future applications. The particles could be used in food and pharmaceutical industries and even in edible films for food packaging.

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