Protein Z is a vitamin K-dependent glycoprotein that is synthesized in the liver. It was first described in 1977 by Prowse and Esnouf. In 1984 it was purified for the first time, and in 1990 the amino acid sequence was clarified. The molecular weight of the protein Z is 62 kD, it consists of a single chain with 396 amino acids. Protein Z acts as a cofactor in the binding of thrombin to the phospholipid surface and is not enzymatically active. Without protein Z, no binding occurs.
A further function of protein Z is the degradation of F-Xa by acting as a cofactor of a "protein-Z-related proteinase inhibitor". In the case of a protein Z deficiency, haemorrhagic diathesis occurs, e.g. in the form of a rumble-leaning phenomenon. The plasma concentration is 2900 ul/l, the half-life of protein Z is 2.5 days.