Albumin

Albumin, especially human serum albumin (HSA), is the most abundant plasma protein in humans. It is synthesized by liver hepatocytes and released into the bloodstream, where it contributes to colloid osmotic pressure and serves as a carrier for various substances.

Structure and properties: It is a single polypeptide chain of about 585 amino acids with a molecular mass of approximately 66.5 kDa. The molecule consists of three homologous domains and possesses numerous binding sites for fatty acids, bilirubin, calcium, hormones, and many drugs, enabling broad ligand transport and regulation of solubility.

Synthesis and turnover: Synthesis occurs in the liver; the half-life in human circulation is about 20 days; catabolized mainly by the reticuloendothelial system. Normal serum concentration is about 3.5-5.0 g/dL, but variable with age and health.

Functions: Maintains intravascular volume; acts as carrier for fatty acids, hormones, bilirubin, calcium, and drugs; pH buffering; scavenges reactive species.

Clinical relevance: Hypoalbuminemia arises from liver disease, nephrotic syndrome, malnutrition, or inflammation and is associated with edema and poorer outcomes. Serum albumin is a routine laboratory measure. Therapeutically, intravenous albumin solutions (typically 5% or 25%) are used for volume expansion in specific clinical settings; routine edema is usually managed with other therapies. Potential adverse effects include allergic reactions, infection risk, and fluid overload; cost is a consideration.

In research and industry, bovine serum albumin (BSA) and recombinant human albumin are used as laboratory reagents, stabilizers, and carriers in assays and vaccines.