Genetic variants of serum albumin: a study of albumin Kashmir.

The study of human serum albumin variants is reviewed with reference to albumin Kashmir, a typical variant. Its published instances are listed and its position in this field of investigations is indicated.     

Bilirubin. Solubility and interaction with albumin and phospholipid.

Bilirubin is generally considered a lipophilic substance, and its neurotoxicity is ascribed to an affinity for lipids in the central nervous system. In the present paper, it is shown that the solubility of bilirubin in apolar solvents and in triglycerides is low and increases with solvent polarity. Consequently, bilirubin should not be characterized as lipophilic. The solubility in aqueous buffers was studied under exclusion of light and was found lower than previously reported, about 7 nM at pH 7.4, temperature 37 degrees C, increasing with higher pH, approximately in inverse proportion with the squared hydrogen ion concentration. Binding of bilirubin to human serum albumin was studied by the rate of oxidation with peroxidase of the free ligand at equilibrium. The stoichiometry of proton involvement in the binding process was investigated by acidimetric titration. It is concluded that precipitation of bilirubin in vivo is thermodynamically possible. It was further demonstrated by light absorption spectroscopy that bilirubin forms a complex with phosphatidylcholine in diethyl ether and that an aqueous suspension of phosphatidylcholine enhanced aggregation of bilirubin. Transfer of bilirubin dianion from its complex with plasma albumin and precipitation of bilirubin acid with phosphatidylcholine in membranes of nerve cells is therefore possible and may account for the neurotoxicity.     

Sites of direct and indirect halogenation of albumin.

The sites of radiohalogenation in proteins vary with the labeling method and the pH of the labeling reaciton. We have directly halogenated albumin with carrier-free radioiodide by three methods (pH range 2.2--9.3), and with carrier-free radiobromide by the chloroperoxidase method (pH range 2.2--4.6). Albumin was also indirectly halogenated by attaching a radioiodinated acylating agent, N-succinimidyl-3-(4-hydroxyphenyl) propionate (SHPP). The labeled proteins were proteolyzed enzymatically at neutral pH and the labeled amino acids produced were analyzed by liquid chromatography. Iodination at pH 7 yielded predominantly monoiodotyrosine, but at lower pH, fewer tyrosyl residues are labeled and a greater number of unstable sulfur-iodine bonds are formed at cysteinyl residues. Bromination with chloroperoxidase resulted in a high degree of labeling of cysteinyl residues at pH 2.8, the condition for optimum activity of this halogenating enzyme. Indirect halogenation with SHPP resulted in labeling of mid-chain lysyl, histidyl and tyrosyl residues.     

Chemical structure of two fragments of human serum albumin and their location in the albumin molecule.

1. 'Inhibitor fragment' isolated from human serum albumin degraded by rabbit cathepsin D is composed of one peptide chain with two intrachain disulphide bonds. There are two kinds of inhibitor molecules having different N-terminal amino acids: one is threonine and the other glutamine. 2. Fragment F1, isolated from inhibitor degraded by trypsin, is composed of two chains linked by a disulphide bond. There are three kinds of fragment F1. All have one alpha chain in common, which has an intrachain disulphide bond. They differ by the nature of the chain, which is linked to the alpha chain by a disulphide bond. The epsilon chain is present in trace amounts. The two other chains, beta and gamma, differ by their C-terminal amino acid, which is respectively arginine and lysine. 3. Inhibitor is composed of the last 92 or 89 residues of the human albumin molecule and fragment F1 is composed of two parts of this C-terminal portion of the albumin molecule.     

Exchange of copper between serum albumin and bleomycin.

1. The present in vitro study shows that bleomycin is able to take up copper from albumin, which functions as a copper transport protein in plasma. 2. Calculations, based on plasma concentrations of Cu(II)-albumin and bleomycin, suggest that only a small fraction of bleomycin (less than 3%) may directly accept copper from Cu(II)-albumin.     

Studies on the carotenoids in the muscle of salmon--V. Combination of astaxanthin and canthaxanthin with bovine serum albumin and egg albumin.

1. Bovine serum albumin (BSA) and/or egg albumin were bound to astaxanthin or canthaxanthin easily and the spectroscopic characteristics of these complexes were similar to those of astaxanthin or canthaxanthin in the salmon muscle. 2. This result indicates that astaxanthin-BSA, -egg albumin, canthaxanthin-BSA and -egg albumin complexes were basically similar to astaxanthin-actomyosin and/or canthaxanthin-actomyosin complex in the salmon muscle. 3. The binding of salmon actomyosin to astaxanthin or canthaxanthin is not specific.