Ivan Goshev

Intrinsic Tryptophan Fluorescence of Human Serum Proteins and Related Conformational Changes

The unfolding of human serum proteins (HSP) was studied by measuring the intrinsic fluorescence intensity at a wavelength of excitation corresponding to tryptophans or typosines fluorescence and surface hydrophobicity. The maxima emission wavelengths (λmax) of human serum albumin (HSA) and human serum globulin (HSG) before beer consumption (BC) were 336.0 and 337.0 nm and after BC shifted to 335.0 and 334.0 nm, respectively. The surface hydrophobicity slightly increased after BC. In a solution of 8 M urea the λmax of BSA shifted to 346.4 and that of BSG to 342.5 nm. In contrast, in the same solution but after BC the λmax positions of HSA and HSG shifted to 355.9 and 357.7 nm, respectively. A decrease in fluorescence intensity, a shift in the maximum of emission, and an increase in surface hydrophobicity which reflected unfolding of proteins were observed. Here we provide evidence that the loosening of the HSP structure takes place primarily in various concentrations of urea before and after beer consumption. Differences in the fluorescence behavior of the proteins are attributed to disruption of the structure of proteins by denaturants as well as by the change in their compactability as a result of ethanol consumption.

Antioxidative Properties of Jaffa Sweeties and Grapefruit and Their Influence on Lipid Metabolism and Plasma Antioxidative Potential in Rats

The effective substances (polyphenols, phenolic and ascorbic acids, flavonoids and dietary fibers) and antioxidative activities, using different radical-scavenging tests, were determined for Jaffa sweeties and grapefruit. The antioxidative activities comprised the contributions from polyphenols, phenolic acids, flavonoids and ascorbate components, and were well-correlated with polyphenols and flavonoids. The correlation coefficient between the polyphenols and antioxidative activity varied from 0.73 to 0.99. All applied methods showed that sweeties had higher antioxidative activity than grapefruit. Experiments on laboratory animals show that diets supplemented with sweeties, and to a lesser extent with grapefruit, increased the plasma antioxidative potential and improved the lipid metabolism, especially in the rats fed with added cholesterol. These findings provide additional characterization of the nutritional value of citrus fruits and their influence on the lipid metabolism in rats.

Isolation and characterization of a trypsin inhibitor from the seeds of kohlrabi (Brassica napus var. rapifera) belonging to the napin family of storage proteins

A trypsin inhibitor with a Km of 5×10−5m has been isolated from kohlrabi (Brassica napus var. rapifera. Subtilisin DY is inhibited only weakly and chymotrypsin not at all. The inhibitor is closely related to napin as determined by amino acid sequence analysis which also showed the inhibitor to be polymorphous. The inhibitor has been further characterized by means of molecular weight determination using SDS gel-electrophoresis and by amino acid analysis, fluorimetry as well as circular dichroism. A simplified method for purification of napins is given.

Stability of Collagen During Denaturation

The stability of calf skin collagen (CSC) type I during thermal and chemical denaturation in the presence of glycerol was investigated. Thermal denaturation of type I collagen was performed in the presence of glycerol or in combination with urea and sodium chloride. The denaturation curves obtained in the presence of urea or sodium chloride retained their original shape without glycerol. These curves were shifted upward proportionally to the glycerol concentration in the reaction medium. This means that glycerol and the denaturants act independently. The explanation is based on the difference in the mechanism of their action on the collagen molecule.

Stabilizing effect of glycerol on collagen type I isolated from different species

Abstract The stabilizing effect of glycerol on type I collagens (C) from rat tail tendon (RTC), calf skin (CSC), human placenta (HPC), and sheep skin (SSC) at elevated temperature and in urea was investigated. The protein denaturation was followed by means of differential UV-spectroscopy. The denaturation temperatures (Td) increased proportionally to the concentration of glycerol in the reaction medium. Equations for the dependence of Td glycerol concentration were derived. The calculated thermodynamic characteristics do not change significantly with increasing glycerol concentration. It was observed that, in the presence of glycerol, the collagen molecule was stabilized, not only by heating, but also by the action of urea.

Characterization of Rapana thomasiana as an indicator of environmental quality of the Black Sea coast of Bulgaria

The aim of this investigation was to determine the contents of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), minerals, trace elements and bioactivity in the gastropod Rapana thomasiana, which can be used as an environmental bioindicator organism. The chemical differences between Rapana thomasiana from polluted (RapaPol) and non-polluted (RapaNPol) sites of the Black Sea coast in Bulgarian were investigated. Chromatography and high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) were used for evaluation of PAHs, PCBs, minerals and trace elements. Methanol extracts from RapaPol and RapaNPol (to a lesser degree) contained relatively high amounts of free phenolics (2.50±0.3 and 1.57±0.18 mg GAE/g DW, respectively) and exhibited the following respective levels of antioxidant activities determined by two radical-scavenging assays (μMTE/g DW): 1.8±0.2 and 0.98±0.08 by 1-diphenyl-2-picrylhydrazyl method (DPPH); 1.74±0.17 and 1.04±0.12 by cupric reducing antioxidant capacity (CUPRAC). The total amounts of elements, PAHs and PCBs were higher in RapaPol than in RapaNPol. The obtained indices of Rapana thomasiana can serve as a bioindicator of the environmental ecological quality.

Biomass, protein- and carbohydrate-composition of phytoplankton in Varna Bay, Black Sea

It was shown that phytoplankton from the Varna Bay, Black Sea, has significantly more suspended carbohydrates, proteins and biomass in July than in April. The dominant species were Bacillariophyceae and Dinophyceae. Electrophoretic and fluorescent spectra have shown the main differences in molecular weight and stability of phytoplankton proteins. Phytoplankton included specific proteins distributed over a limited range of molecular weights between 14 and 72 kilodaltons (kDa). The most abundant protein constituents in phytoplankton samples collected in April were around 45–55 kDa. The seasonal variations of the environment influence the quantitative and qualitative changes in phytoplankton.

ANTIOXIDANT CAPACITY OF PEA (PISUM SATIVUM L. CV. RAN) PLANTS DETERMINED BY DIFFERENT ANALYTICAL METHODS

The change in the antioxidant capacity (AOC) of pea plants during vegetative growth was followed by means of hydroxyl radical averting capacity (HORAC), oxygen radical absorbance capacity (ORAC) and Folin–Ciocalteau (F–C) assays. During the studied period the pea plants developed all leaf stages before flower formation; root and shoot biomasses enhanced, which was accompanied by an increase of AOC. Highest AOC was localized in the green organs such as leaves, especially those in the growing apical part; stem and root AOC were lower. AOC increased during the organ growth; it was expressed in different magnitude by the three assays. Most likely the assays reflected the antioxidant properties of different compounds. The contribution of potential non-enzymatic antioxidants in the applied assays was discussed.