ABSTRACT
A study has been made on the properties of human serum albumin (HSA) binding sites and how they are modified by pre-oxidation of the protein with hypochlorite. The oxidation extent was assessed from changes in the protein intrinsic fluorescence and production of carbonyl groups. HSA retains its solute binding capacity even after exposure to relatively large amounts of hypochlorite (up to 40 oxidant molecules per protein). From an analysis of the binding isotherms of dansyl sarcosine (DS) and dansyl-1-sulfonamide (DNSA) to native and hypochlorite treated albumin it is concluded that pre-oxidation of the protein reduces the number of active sites without affecting the binding capacity of the remaining binding sites. From DS and DNSA fluorescence anisotropy, Laurdan anisotropy and generalized polarization measurements, it is concluded that both Sites I and II in the native protein provide very rigid environments to the bound probes. These characteristics of the sites remain even after extensive treatment with hypochlorite. This stubbornness of HSA could allow the protein to maintain its function along its in vivo lifetime.
Subject(s)
Fluorescence , Hypochlorous Acid/pharmacology , Serum Albumin/chemistry , Binding Sites/drug effects , Dansyl Compounds/metabolism , Fluorescence Polarization , Humans , Ligands , Oxidation-Reduction , Protein Binding/drug effects , Sarcosine/metabolism , Serum Albumin/metabolism , Titrimetry , Tryptophan/metabolismABSTRACT
A conjugation method for coupling probes bearing hydrazine or primary amino groups to a lipopolysaccharide (LPS) is described. LPS is modified through the hydroxyl groups present in its O-antigen moiety by activation with cyanogen bromide in aqueous acetone using triethylamine to enhance the electrophilicity of CNBr. The method yields conjugates with good labeling ratios, preserving the endotoxic activity of the lipid A moiety, which in blood exerts pleiotropic effects on many tissues and organs, resulting in multiple-organ damage, circulatory collapse, and death. Conjugation of smooth-form LPS from Salmonella enterica sv. Minnesota to dansyl hydrazine yielded a labeling ratio of 330 nmol dansyl/mg LPS, with nearly no loss of the original endotoxic activity. In the case of horseradish peroxidase, in which a spacer was introduced, the ratio was 28 nmol HRP/mg of LPS, preserving 65% of the original endotoxic activity. This work shows that under these conditions of CNBr activation, the labeling process has practically no effect on the endotoxic behavior of LPS. The method can be used effectively for the conjugation of LPS to probes bearing primary amino, hydrazine, or hydrazide functional groups.
Subject(s)
Amines/chemistry , Chemistry Techniques, Analytical/methods , Dansyl Compounds/chemistry , Hydrazines/chemistry , Molecular Probes/chemistry , Polysaccharides, Bacterial/metabolism , Salmonella enterica/chemistry , Amines/metabolism , Dansyl Compounds/metabolism , Electrophoresis , Horseradish Peroxidase/metabolism , Hydrazines/metabolism , Molecular Probes/metabolism , Polyethylene Glycols/chemistry , Polysaccharides, Bacterial/chemistry , Spectrometry, Fluorescence , Spectrometry, Mass, Matrix-Assisted Laser Desorption-IonizationABSTRACT
The binding of some cephalosporins to human serum albumin was studied using probes for the so-called I, II, bilirubin and fatty acids binding sites. The results showed that cephradine and cefsulodin bind to site II, cefaclor, cefamandole, cefsulodin, cephaloglycin and cefadroxil bind to the bilirubin binding site, while cefaclor does it to the fatty acid binding site. No binding of these cephalosporins to site I of albumin was found. The binding produced a perturbation on the N-B equilibrium of albumin, stabilizing the N conformational form, which suggests that the N form of albumin has more affinity with the cephalosporins than the B form. This finding gives support to the assumption that the binding of cephalosporins to site II, bilirubin and fatty acids binding sites affects the N-B transition of albumin.