Mathematical modeling and study of mass transfer parameters in supercritical fluid extraction of fatty acids from Trout powder

Mathematical modeling of fatty acids (FAs) extraction from Trout powder by supercritical carbon dioxide was performed in the present work. Trout powder with its low cost contains high amount of essential FAs and it is commonly available as a proper source of FAs. The effect of process parameters, such as pressure (25, 28, 31, 34 and 37 MPa) and temperature (310, 318 and 326 K) of extraction and void fraction of the bed (0.25, 0.35 and 0.45, v/v) on the yield of FAs extraction was examined in a series of experiments conducted in a laboratory scale apparatus. The results indicated a significant increase of extraction yield with an increase of pressure from 25 to 34 MPa, but working at the higher pressure (37 MPa) caused reduction of the extract. Increasing the temperature higher than 318 K revealed significant reduction of the FAs yield and increasing the bed void fraction from 0.25 to 0.45 showed enhancement of the extraction.

The mathematical model was developed considering diffusion-controlled regime in the particle and film mass transfer resistance around the particle with axial dispersion of the bulk phase at dynamic conditions. Henry law was used to describe the equilibrium state of solid and fluid phases. The proposed mass balance equations were numerically solved using implicit finite difference method and the model parameters were correlated using the experimental results of the outlet FAs concentration in the oil extracted at dynamic conditions. Well-known Nelder–Mead method was applied to estimate the four parameters of the model, namely, mass transfer coefficient (k_f), axial dispersion coefficient (D_ax) in the bulk phase, effective diffusivity (D_eff) into the pores and Henry coefficient (H). In the range of studied conditions, the higher extraction efficiency with higher pressure resulted lower correlated H, although the temperature increasing which showed a retrograde phenomena in the FAs yield, revealed H passing though a minimum.     

DNA adducts with antioxidant flavonoids: morin, apigenin, and naringin

Flavonoids have recently attracted a great interest as potential therapeutic drugs against a wide range of free-radical-mediated diseases. The anticancer and antiviral activities of these natural products are implicated in their mechanism of actions. While the antioxidant activity of these natural polyphenolic compounds is well known, their bindings to DNA are not fully investigated. This study was designed to examine the interactions of morin (Mor), naringin (Nar), and apigenin (Api) with calf thymus DNA in aqueous solution at physiological conditions, using constant DNA concentration (6.25 mM) and various drug/DNA(phosphate) ratios of 1/40 to 1. FTIR and UV-Vis spectroscopic methods were used to determine the ligand binding modes, the binding constant, and the stability of DNA in flavonoid-DNA complexes in aqueous solution. Spectroscopic evidence shows both intercalation and external binding of flavonoids to DNA duplex with overall binding constants of K(morin) = 5.99 x 10(3) M(-1), K(apigenin) = 7.10 x 10(4) M(-1), and K(naringin) = 3.10 x 10(3) M(-1). The affinity of ligand-DNA binding is in the order of apigenin > morin > naringin. DNA aggregation and a partial B- to A-DNA transition occurs upon morin, apigenin, and naringin complexation.     

The adventures of sonic hedgehog in development and repair. III. Hedgehog processing and biological activity

The Hedgehog (Hh) family of secreted proteins is necessary for aspects of the development and maintenance of the gastrointestinal tract. Hh is thought to function as a morphogen, a mitogen, a cell survival factor, and an axon guidance factor. Given its wide role in development, as well as in a variety of disease states, understanding the regulation of Hh function and activity is critically important. However, the study of Hh signaling has been impeded by its unusual biology. Hh is unique in that it is the only protein covalently modified by cholesterol, which in turn affects numerous aspects of its localization, release, movement, and activity. All are important factors when considering Hh's physiological role, and animals have developed an intricate system of regulators responsible for both promoting and inhibiting the activity of Hh. This review is intended to give a broad overview of how the biosynthesis and movement of Hh contributes to its biological activity.     

The dual specificity phosphatase Cdc25B, but not the closely related Cdc25C, is capable of inhibiting cellular proliferation in a manner dependent upon its catalytic activity

Cdc25B and Cdc25C are closely related dual specificity phosphatases that activate cyclin-dependent kinases by removal of inhibitory phosphorylations, thereby triggering entry into mitosis. Cdc25B, but not Cdc25C, has been implicated as an oncogene and been shown to be overexpressed in a variety of human tumors. Surprisingly, ectopic expression of Cdc25B, but not Cdc25C, inhibits cell proliferation in long term assays. Chimeric proteins generated from the two phosphatases show that the anti-proliferative activity is associated with the C-terminal end of Cdc25B. Indeed, the catalytic domain of Cdc25B is sufficient to suppress cell viability in a manner partially dependent upon its C-terminal 26 amino acids that is shown to influence substrate binding. Mutation analysis demonstrates that both the phosphatase activity of Cdc25B as well as its ability to interact with its substrates contribute to the inhibition of cell proliferation. These results demonstrate key differences in the biological activities of Cdc25B and Cdc25C caused by differential substrate affinity and recognition. This also argues that the antiproliferative activity of Cdc25B needs to be overcome for it to act as an oncogene during tumorigenesis.     

Modifying histones and initiating meiotic recombination; new answers to an old question

It is well documented that the formation of the DNA double-strand breaks (DSBs) that initiate meiotic recombination is influenced by chromatin and larger scale chromosome organization, but the molecular nature of this influence has remained elusive. Several recent studies, including (this issue of Cell), shed light on this issue by revealing roles for posttranslational histone modifications in promoting DSB formation.