Albumin

Properties and structure

Albumins are generally compact and soluble at physiological pH. They have multiple binding sites that allow reversible attachment of small molecules, ions and some drugs. Many albumins are heat sensitive: albumin in egg whites denatures and coagulates when heated, which is the basis for cooking changes in texture. In the body, serum albumin is synthesized mainly by the liver and circulates in plasma.

Functions and common uses

Albumins perform several important biological and practical roles. Key functions include:

• Maintaining colloid (oncotic) pressure in blood vessels, which helps regulate fluid distribution between vascular and tissue compartments.
• Transporting fatty acids, hormones, bilirubin and many drugs through the bloodstream by reversible binding.
• Acting as an antioxidant and a reservoir for nutrients and metal ions.

Outside physiology, purified albumins such as bovine serum albumin (BSA) are widely used in laboratories as stabilizers, blocking agents and standards. Human albumin solutions are also used clinically as volume expanders in specific medical situations.

Measurement, indicators and examples

Albumin levels are measured in medical tests; low serum albumin can indicate liver disease, malnutrition or fluid imbalance, while the presence of albumin in urine (albuminuria) can signal kidney damage. In food and quality testing, the "albumin index" is a simple measure of egg freshness that records how far the liquid egg white spreads when the shell is broken on a flat surface: fresher eggs hold the white more compactly.

History, terminology and distinctions

The name derives from the Latin albumen, originally meaning egg white. Historically, albumin and its preparations have been used in photography, bookbinding and art as adhesives and clarifiers. It is helpful to distinguish the biochemical term "albumin" from the older culinary term "albumen" (egg white) and from related plasma proteins such as globulins, which differ in solubility and function.

Notable facts

Because albumin binds many small molecules, it affects the pharmacokinetics of drugs and the interpretation of some laboratory assays. Its central role in maintaining vascular volume and transporting substances makes it a protein of broad clinical and scientific significance.