Comparative effects of limited tryptic hydrolysis on physicochemical and structural features of seed 11S globulins

The effect of the limited proteolysis by trypsin on selected seed storage 11S globulins (broad bean and pea legumins, glycinin and helianthinin) was studied by high-sensitive differential scanning calorimetry, fluorescence spectroscopy and analysis of proteolysis kinetics. Different behaviour of glycinin and helianthinin, on one hand, and broad bean and pea legumins, on the other, were observed: in the first group changes in the physicochemical characteristics of the proteins due to their limited proteolysis are more pronounced in comparison with the second one, in relation with the extent of primary structure modifications. The differences observed have been evaluated in relation with the amino acid sequence features of the four 11S globulin studied and agree with the literature data concerning the protein structural changes in the course of the limited proteolysis.     

A study of dilute aqueous solutions of humic acids by scanning microcalorimetry

It has been found by reversed-phase chromatography that humic acids obtained from vermicomposts of different duration of vermicomposting consist of a hydrophilic and a hydrophobic fractions, the hydrophobic fraction having a substantially lower content of charged, probably carboxylic, groups. A change in the sign of the temperature dependence of the heat capacity of dilute aqueous solutions of humic acids at ∼58°C has been found by differential scanning microcalorimetry, which indicates an increase in the hydration of hydrophobic groups. A jump-wise increase in heat capacity in the temperature range from 86 to 90°C was also found, which is perhaps due to hydration of hydrophobic groups in the interior of “micelles“, because of “devitrification” of the hydrophobic nucleus of micelle-like structures. It was shown that increasing the duration of vermicomposting leads to an increase in the relative content of the hydrophobic fraction of humic acids and in the cooperativity of the thermodynamic transition, which manifests itself as the jump of heat capacity, which probably results from the increase in the “micelle” size.     

Phylogeny and expression of carbonic anhydrase-related proteins

Background  

Carbonic anhydrases (CAs) are found in many organisms, in which they contribute to several important biological processes. The vertebrate α-CA family consists of 16 subfamilies, three of which (VIII, X and XI) consist of acatalytic proteins. These are named carbonic anhydrase related proteins (CARPs), and their inactivity is due to absence of one or more Zn-binding histidine residues. In this study, we analyzed and evaluated the distribution of genes encoding CARPs in different organisms using bioinformatic methods, and studied their expression in mouse tissues using immunohistochemistry and real-time quantitative PCR.     

Structural study of the solutions of acidic polysaccharides. II. Study of some thermodynamic properties of the dilute pectin solutions with different degrees of esterification

Light-scattering and surface tension measurements have been used to study the structure and thermodynamic properties of aqueous-salt solutions of pectins, with the degree of esterification (DE) varying from 5 to 100%. Pectin macromolecules were found in the form of aggregates with $\text{M}{}_{\mathrm{w}}\text{= 5 × 10}{}^5\text{to}\text{1·1 × 10}{}^6\text{D}$. The second virial coefficient of pectin was negative in these poor solvents and independent of the DE. Pectins exhibited surface activity at the air-water interface, the magnitude of this activity also being independent of the DE.     

Detoxification of ochratoxin A,a food contaminant: Prevention of growth of Aspergillus ochraceus and its production of ochratoxin A

The toxicity of ochratoxin A (OTA), a mycotoxin produced by fungi ofAspergillus orPenicillium genera is now well documented. Its nephrotoxicity, immunosuppression, teratogenicity, and carcinogenicity have been widely studied. Physical and biochemical methods have been studied to prevent these toxinogenicAspergillus andPenicillium from producing OTA, and/or to destroy the mycotoxin when already produced in a liquid or a solid medium. Repeated freezing at ? 20?C and thawing at + 26?C aleatory reduce OTA production in a liquid medium. Exposure to UV B for different periods of time is efficient in preventing OTA production in a liquid medium. Gamma-irradiation from 2 to 5 kGy gives good results in preventing the production of OTA or destroying it when already produced. Carboxypeptidase is very efficient at 5 units/50 ml in a liquid medium for cleaving the OTA already produced.     

Structural studies of the solutions of anionic polysaccharides. IV. Study of pectin solutions by light-scattering

Aqueous solutions of pectins, with a degree of esterification (DE) varying from 0 to 95%, have been studied by light-scattering. A set of samples of similar molecular sizes were prepared by methylation of sodium pectate with diazomethane. The solutions were subjected to ultracentrifugation to ensure the removal of small amounts of gel fraction. The second virial coefficient of pectin was positive and constant for DE values varying between 43 and 95%, but increased by a factor of three when the DE was reduced to zero. This increase is at least partly due to coulombic electrostatic interactions. All of the pectins investigated behaved as semi-rigid-chain polymers. The chain flexibility was a maximum in the DE range 43 to 58%.In pectin solutions with a DE higher than 58% attractive forces exist between pectin macromolecules due to the presence of ester groups. It is expected that the interactions between ester groups contribute to both the chain rigidity and the gel-forming ability of pectins.     

Limited tryptic hydrolysis of pea legumin: molecular mass and conformational stability of legumin-T

The investigation of hydrodynamic and thermodynamic properties and the determination of the molecular mass of legumin-T, the product of limited tryptic hydrolysis of the 11-S-globulin from pea seeds, was carried out to ascertain the structural relationship to globulin-T's from other legumin-like proteins. The obtained legumin-T preparation has a molecular mass M(W)=260+/-10 kDa and M(S,D)=270+/-20 kDa. The secondary structure of legumin-T is characterised by a high percentage of beta-sheet conformation, comparable to that of native legumin and a reduced percentage of helical conformation. The conformational stability of legumin-T evaluated by equilibrium unfolding in the presence of guanidinium chloride was only slightly reduced in comparison to the native legumin, whereas the calorimetrically determined denaturation enthalpy and Gibbs energy of denaturation were found to be increased for legumin-T. These physicochemical properties are very similar to those of faba bean legumin-T.