Albumin refers to a 65–70 kDa family of globular proteins, the most common of which are the serum albumins. Albumins are widely found in blood plasma and differ from other blood proteins in that they are not glycosylated. Serum albumin is the most abundant blood plasma protein and forms a large proportion of all plasma protein.
In humans, human albumin (HA) constitutes approximately 50% of the total plasma protein content. HA is a small globular protein consisting of a single chain of 585 amino acids organised in three repeated homologue domains, sites I, II, and III, each composed two separate sub-domains, A and B. HA is produced in the liver by hepatocytes and its synthesis is stimulated by hormones such as insulin, cortisol and growth hormone, and inhibited by pro-inflammatory substances such as interleukin-6 and tumour necrosis factor-α1. HA is mainly catabolised in the muscles, liver and kidneys.
Serum albumins are important in regulating blood volume by maintaining the oncotic pressure of the blood compartment and maintaining fluid balance in the body. They also serve as carriers for poorly water soluble molecules including hormones, bile salts, unconjugated bilirubin, free fatty acids, ions, and some drugs, with important consequences for their solubilisation, transport, metabolism, and detoxification