TLDR: Albumin is a type of protein that is found in the blood and other bodily fluids. It helps transport various substances throughout the body.

Albumin is a family of proteins, with the most common type being serum albumin. These proteins are soluble in water and can be found in blood plasma. They are different from other blood proteins because they are not glycosylated, which means they don't have sugar molecules attached to them. Albumins are known for their ability to bind to different substances and carry them around the body.

There are several types of albumins found in humans, including human serum albumin, alpha-fetoprotein, vitamin D-binding protein, and afamin. These proteins have different functions, such as regulating the oncotic pressure of blood, binding to hormones and fatty acids, and carrying vitamin D and Wnt proteins.

Albumins can also be found in other animals and plants. For example, ovalbumin is a storage protein found in egg white, while lactalbumin is a protein fraction of milk. Some plant seeds also contain albumins, which have coagulation properties similar to egg whites.

The structure of albumin has been studied using X-ray crystallography, and it consists of three homologous domains that assemble to form a heart-shaped protein. Each domain contains subdomains that have common structural motifs. The ligand binding sites of albumin are located in hydrophobic cavities in certain subdomains.

Albumins have various medical and biotechnological uses. They are used in clinical medicine to regulate oncotic pressure and as carriers for drugs and other substances. Bovine serum albumin is commonly used in biotechnology, but versions from humans and genetically-modified rice are also used to reduce animal cruelty.

In addition to the albumins found in vertebrates, there are other proteins that are sometimes referred to as albumins. These include ovalbumin, which is a storage protein in egg white, and lactalbumin, which is a protein fraction of milk.

Overall, albumins are important proteins that play a crucial role in transporting substances throughout the body. They have diverse functions and can be found in various biological fluids.