Heat denaturation of serum albumin monitored by 1-anilino-naphthalene-8-sulfonate

Differentiation of glycated residue numbers on heat-induced structural changes of bovine serum albumin

BACKGROUND

Glycation is an approach in dealing with heat-induced protein aggregation. The relationship between degree of glycation and heat-induced structural changes is still unclear. The present work investigates the effect of different numbers and sites of glycated residues on heat-induced structural changes of bovine serum albumin (BSA). Glycation of BSA was carried out with xylose (Xyl) and galactose (Gal) by Maillard reaction. Glycated residues in BSA were identified by liquid chromatography-tandem mass spectrometry, and heat-induced protein structural changes were characterized by fluorescence emission and synchronous fluorescence spectra, 8-anilino-1-naphthalenesulfonic acid fluorescence, Fourier transform infrared (FTIR) and circular dichroism (CD) spectra.

RESULTS

The numbers of glycated residues were 2 and 13 when BSA was glycated by Gal (BSA - Gal) and Xyl (BSA - Xyl), respectively. There were shifts of maximum wavelengths and decreases in fluorescence intensities for both intrinsic and extrinsic fluorescences; shifts of FTIR amide I, III, and A bands; and decrease or increase of CD band intensities, α-helix and β-sheet percentages when BSA was heated. Glycation with Gal or Xyl restrained in similar degrees those changes, including fluorescence wavelengths, amide I band, CD band intensities, and α-helix and β-sheet percentages.

CONCLUSION

Xyl glycated more residues than Gal, while their effects were similar in restraining heat-induced BSA structural changes. © 2017 Society of Chemical Industry.

Chemically Modified Glucose Oxidase with Enhanced Hydrophobicity: Adsorption at Polystyrene, Silica, and Silica Coated by Lipid Monolayers

Covalent modification of glucose oxidase from Aspergillus niger by the palmitic acid ester of N-hydroxysuccinimide at a molar ratio ester:protein of 56:1 results in the formation of the enzyme derivative with 11 attached palmitic chains. Surface hydrophobicity measurements by a fluorescent probe, 8-anilino-1-naphthalenesulfonate, indicate a drastic increase in the hydrophobicity index of glucose oxidase after such a modification. The modified glucose oxidase displays a much higher adsorption affinity for hydrophilic (silica) as well as for hydrophobic (silica coated by phosphatidyl choline and cholesterol monolayers and polystyrene latex beads) surfaces, and forms more compact surface layers compared to the native glucose oxidase. Such a difference results from a spontaneous formation of micelle-like aggregates (clusters) of the hydrophobized enzyme molecules (average size 500 nm), which come into contact with a surface. A possible structure of the glucose oxidase surface layers and the nature of the forces determining the adsorption of the enzyme on various adsorbents are discussed. Copyright 1999 Academic Press.

Chemically Modified Human Immunoglobulin G: Hydrophobicity and Surface Activity at Air/Solution Interface

Covalent modification of human IgG by fatty acid esters (C8 and C16) of N-hydroxysuccinimide was carried out. Surface hydrophobicity measurements, using the fluorescent probe 8-anilino-1-naphthalenesulfonate, indicate an increase in the surface protein hydrophobicity with an increase in the number and in the length of the attached alkyl chains. The modified IgGs decrease surface tension at the air/solution interface more effectively than the native protein. The values of the molecular cross-sectional areas (DeltaA) estimated from the kinetic data are in the range of 100-300 Å2 and reflect the size of protein segments at the interface during the adsorption process. About 40-50% increase in the DeltaA was observed upon attachment of the C8 groups to the native IgG. The lengthening of the bound alkyl chain from C8 to C16 results in a further increase in this value. The influence of the overall IgG hydrophobicity and the length of the attached alkyl chain on the dimensions of the mobile protein segment at the surface are discussed. Copyright 1999 Academic Press.

Formation of Surface Active Gelatin by Covalent Attachment of Hydrophobic Chains

Surface active gelatin was formed by covalent attachment of hydrophobic groups to gelatin molecules. The modification was carried out at various degrees of attachment and with various chain lengths. These modified gelatins (MGs) were synthesized in dry DMSO by a simple and rapid method. The new method leads to high yields and allows high degrees of modification. The MGs, which have various hydrophobicities, have better surface activity than the native gelatin, as determined by surface tension reduction. The surface tension reduction is correlated to the hydrophobicity of the modified molecule, which was determined by a fluorescent probe. It appears that both the increase in the number of the hydrophobic groups and the increase in the chain lengths lead to decreased surface tension. Copyright 1997 Academic Press. Copyright 1997Academic Press

Role of serum in inhibition of cultured lymphocytes by lysophosphatidylcholine

Serum was heated at various temperatures to inactivate components which might be involved in the regulation of lysophosphatidylcholine (lysoPC) levels in rabbit lymph-node cell cultures. Cells cultured in medium containing serum preheated for 20 min at 66 degrees C ("66 degrees C-serum") were inhibited much more by exogenous lysoPC (5 microM) than were cells cultured in medium containing control serum ("38 degrees C-serum"). This was observed over a 20 h culture period as a slow increase in inhibition of cell labelling with [3H] uridine, which reflected cytotoxic cell damage. Heating serum at 66 degrees C caused (i) conversion of monomeric albumin to highly polymeric forms which were deficient in lysoPC-binding activity, (ii) transfer of lysoPC from albumin to lipoproteins, predominantly high density lipoproteins, and (iii) inhibition of two lysoPC metabolizing activities (which were detected only at low levels in control serum). Addition of albumin to cultures containing 66 degrees C-serum decreased the toxicity of lysoPC to the same extent as did the addition of control serum with an equivalent albumin content. Thus, albumin was the major heat-labile factor protecting cells against lysoPC. However, cell inhibition by lysoPC was dependent on the sequence of heating serum and lysoPC addition. Inhibition was small when lysoPC was added before heating the serum. This could not be explained by a detectable difference in the binding of lysoPC to serum components. Furthermore, although radioactive labelling of cells with [14C] lysoPC was increased in 66 degrees C-serum, this did not correlate with cell inhibition. Increased labelling with [14C] lysoPC occurred several hours before significant cell inhibition was evident and was not affected by the sequence of heating and lysoPC addition. Since preincubation of lysoPC with 66 degrees C-serum increased the inhibition, it is suggested that the heated serum lysoPC generates another factor which is responsible for the cytotoxic effects observed.