Tryptophan fluorescence intensity and anisotropy decays of human serum albumin resulting from one-photon and two-photon excitation.

We measured the emission spectra, intensity decays and anisotropy decays of the single tryptophan residue of human serum albumin (HSA) resulting from one-photon (295-298 nm) and two-photon (590-596) excitation. The emission spectra and intensity decays were independent of the mode of excitation. The anisotropy decays were superficially similar for one- and two-photon excitation. However, upon consideration of the different orientation photoselection for one- and two-photon excitation, the anisotropy data reveal different angles between the absorption and emission oscillators for one-photon and two-photon excitation. This result suggests different relative one-photon and two-photon cross-sections for the 1La and 1Lb transitions of the indole residue. This first report of the time-resolved anisotropy decay of a protein resulting from two-photon excitation suggests that such measurement will yield insights into the complex photophysical properties of tryptophan residues in proteins.     

Changes of net charge and alpha-helical content affect the pharmacokinetic properties of human serum albumin

The pharmacokinetics of 17 genetic variants of human serum albumin with single-residue mutations and their corresponding normal albumin were studied in mice. In all cases, the plasma half-life was affected, but only variants with +2 changes in charge prolonged it, whereas changes in hydrophobicity decreased it. Good positive and negative correlations were found between changes in alpha-helical content taking place in domains I+III and domain II, respectively, and changes in half-lives. No correlation was found to type of mutation or to changes in heat stability as represented by DeltaH(v). Liver and kidney uptake clearances were also modified: alpha-helical changes of domains I+III showed good negative correlations to both types of clearances, whereas changes in domain II only had a good positive correlation to kidney uptake clearance. No correlation between the other molecular changes and organ uptakes was observed. The relatively few correlations between changes in molecular characteristics and the organ uptakes of the variants are most probably due to different handling by plasma enzyme(s) and the various types of cell endocytosis. Of the latter, most lead to destruction of albumin, but at least one results in recycling of the protein. The present information should be useful when designing recombinant, therapeutical albumins or albumin products with a modified plasma half-life.     

Redox properties of serum albumin

Background

Oxidative damage results in protein modification, and is observed in numerous diseases. Human serum albumin (HSA), the most abundant circulating protein in the plasma, exerts important antioxidant activities against oxidative damage.

Scope of review

The present review focuses on the characterization of chemical changes in HSA that are induced by oxidative damage, their relevance to human pathology and the most recent advances in clinical applications.

Major conclusions

The antioxidant properties of HSA are largely dependent on Cys34 and its contribution to the maintenance of intravascular homeostasis, including protecting the vascular endothelium under disease conditions related to oxidative stress. Recent studies also evaluated the susceptibility of other important amino acid residues to free radicals. The findings suggest that a redox change in HSA is related to the oxidation of several amino acid residues by different oxidants. Further, Cys34 adducts, such as S-nitrosylated and S-guanylated forms also play an important role in clinical applications. On the other hand, the ratio of the oxidized form to the normal form of albumin (HMA/HNA), which is a function of the redox states of Cys34, could serve as a useful marker for evaluating systemic redox states, which would be useful for the evaluation of disease progression and therapeutic efficacy.

General significance

This review provides new insights into our current understanding of the mechanism of HSA oxidation, based on in vitro and in vivo studies.This article is part of a Special Issue entitled Serum Albumin.     

Biosynthesis of Rat serum albumin

1. The labelling of intracellular and extracellular serum albumin was studied in liver slices and in whole rats by using new methods for the purification of the protein. 2. The results suggest that a polypeptide precursor is formed that is converted relatively slowly into serum albumin. 3. The effect of liver cell K(+) has been examined by a double-label method and it is shown that K(+) accelerates the rate of conversion of ;precursor' into albumin. The rate of transit of albumin across the cell membrane appears to be unrelated to the concentration of K(+) within the cell. 4. The time-course of incorporation of radioactive amino acid into albumin follows a sigmoidal mode. There is a pronounced time-lag before label starts to appear in intracellular albumin, and a further time-lag before it appears in extracellular albumin. 5. In slices the sum of intra- and extra-cellular label rises steadily from 30min after the start of labelling with a pulse of labelled leucine or valine and continues to rise for at least another 60min. This occurs whether labelling is stopped by addition of excess of carrier amino acid or with cycloheximide (100mum) or both. 6. The intracellular albumin content remains constant whether slices are maintained with low or normal intracellular K(+) concentrations. 7. Specific radioactivities of intracellular albumin (and fractions thereof) and of extracellular albumin were determined in vitro and in vivo. The results show that the intracellular albumin cannot be a precursor of extracellular albumin, unless a very small compartment is turning over much more rapidly than the bulk of the liver albumin or even of the microsomal albumin.     

Polymorphism of canine serum albumin

Three serum albumin phenotypes were observed in a population of 257 dogs consisting of 18 breeds and breed crosses. Canine serum albumins are controlled by an autosomal locus with two codominant alleles Alb^F and Alb^S. Separation of the albumin types was possible by using buffer solutions with a pH of about 4.     

Interaction of ergosterol with bovine serum albumin and human serum albumin by spectroscopic analysis

This study was designed to examine the interactions of ergosterol with bovine serum albumin (BSA) and human serum albumin (HSA) under physiological conditions with the drug concentrations in the range of 2.99-105.88?μM and the concentration of proteins was fixed at 5.0?μM. The analysis of emission spectra quenching at different temperatures revealed that the quenching mechanism of HSA/BSA by ergosterol was the static quenching. The number of binding sites n and the binding constants K were obtained at various temperatures. The distance r between ergosterol and HSA/BSA was evaluated according to F?ster non-radioactive energy transfer theory. The results of synchronous fluorescence, 3D fluorescence, FT-IR, CD and UV-Vis absorption spectra showed that the conformations of HSA/BSA altered in the presence of ergosterol. The thermodynamic parameters, free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS) for BSA-ergosterol and HSA-ergosterol systems were calculated by the van't Hoff equation and discussed. Besides, with the aid of three site markers (for example, phenylbutazone, ibuprofen and digitoxin), we have reported that ergosterol primarily binds to the tryptophan residues of BSA/HSA within site I (subdomain II A).     

Bilirubin binding properties of pigeon serum albumin and its comparison with human serum albumin

Binding of bilirubin (BR) to pigeon serum albumin (PgSA) was studied by absorption, fluorescence and CD spectroscopy and results were compared with those obtained with human serum albumin (HSA). PgSA was found to be structurally similar to HSA as judged by near- and far-UV CD spectra. However, PgSA lacks tryptophan. Binding of BR to PgSA showed relatively weaker interaction compared to HSA in terms of binding affinity, induced red shift in the absorption spectrum of BR and CD spectral characteristics of BR-albumin complexes. Photoirradiation results of BR-albumin complexes also showed PgSA-bound BR more labile compared to HSA-bound BR.     

Changes of net charge and α-helical content affect the pharmacokinetic properties of human serum albumin

The pharmacokinetics of 17 genetic variants of human serum albumin with single-residue mutations and their corresponding normal albumin were studied in mice. In all cases, the plasma half-life was affected, but only variants with + 2 changes in charge prolonged it, whereas changes in hydrophobicity decreased it. Good positive and negative correlations were found between changes in α-helical content taking place in domains I + III and domain II, respectively, and changes in half-lives. No correlation was found to type of mutation or to changes in heat stability as represented by ΔH_v. Liver and kidney uptake clearances were also modified: α-helical changes of domains I + III showed good negative correlations to both types of clearances, whereas changes in domain II only had a good positive correlation to kidney uptake clearance. No correlation between the other molecular changes and organ uptakes was observed. The relatively few correlations between changes in molecular characteristics and the organ uptakes of the variants are most probably due to different handling by plasma enzyme(s) and the various types of cell endocytosis. Of the latter, most lead to destruction of albumin, but at least one results in recycling of the protein. The present information should be useful when designing recombinant, therapeutical albumins or albumin products with a modified plasma half-life.     

Thermal aggregation of bovine serum albumin at different pH: comparison with human serum albumin

We report here a study on thermal aggregation of BSA at two different pH values selected to be close to the isoelectric point (pI) of this protein. Our aim is to better understand the several steps and mechanisms accompanying the aggregation process. For this purpose we have performed kinetics of integrated intensity emission of intrinsic and extrinsic dyes, tryptophans and ANS respectively, kinetics of Rayleigh scattering and of turbidity. The results confirm the important role played by conformational changes in the tertiary structure, especially in the exposure of internal hydrophobic regions that promote intermolecular interactions. We also confirm that the absence of electrostatic repulsion favours the disordered non-specific interactions between molecules and consequently affects the aggregation rate. Finally, the comparison between BSA and another relative protein, HSA, allows us to clarify the role of different domains involved in the aggregation process. Proceedings of the XVIII Congress of the Italian Society of Pure and Applied Biophysics (SIBPA), Palermo, Sicily, September 2006.