What is a protein?

Proteins are complex organic compounds, consisting of long strings of amino acids, which contain carbon, hydrogen, oxygen, nitrogen and usually sulphur. They are essential constituents of living cells and are found in both plants and animals.

What do proteins do?

There are hundreds upon hundreds of different proteins and together they are involved in blood coagulation (clotting), oxygen transport, muscle contraction, electron transport and other activities throughout the body, including types which serve as enzymes and hormones. Twenty-one different amino acids are commonly found in proteins and each protein has a unique, genetically defined amino acid sequence which determines its specific shape and function.

Protein S

Protein S is a Vitamin K-dependent plasma glycoprotein which functions as a cofactor to Protein C in the inactivation of Factors Va and VIIIa. It was thought that most of the circulating protein S was produced by hepatocytes in the liver but new research has shown that the endothelial cells lining blood vessels contribute about half of the Protein S. In the circulation, Protein S exists in two forms: a free form and a complex form bound to complement protein C4b. Only the free form has cofactor activity.

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Last updated: Monday, 7th April 2014, © 2000-2017

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