Phospholipids blood, physiological role

In mammals and birds vitamin K] is an essential cofactor in the posttranslational carboxy lation reaction of glutamic acid residues (GLU) to y-carboxygiutamic acid residues (GLA) in a number of blood clotting factors (factors II, VII, IX, and X) and also in some other proteins, such as protein C, protein S and osteocalcin. These GLA residues provide the proteins with calcium-binding properties essential for the interaction with phospholipids and for their activation. Excellent articles and reviews on the biochemistry and on the physiological role of vitamin Kj in humans are given by Suttie (70), Friedman (71), and Friedrich (72). Besides vitamin K itself, ubiquinones and plastoquinones also occur in higher plants. Structures of vitamin Ki and of some of these related compounds are presented in Fig. 7. 

Such microvesicles have size variable between 50 nm to 1 (xm and differ from other vesicles (like exosomes (30-100 nm)). In general, microparticles are phospholipids vesicles derived from eukaryotic cells as a result of different types of stimulation. Microparticles can also be defined as phospholipids microvesicles containing certain membrane proteins originating from the parental cell. Microparticles circulate in the blood and contribute to numerous physiological processes. MPs have been described in various haematopoietic cells as platelets (Heijnen et al. 1999), T-cells (Blanchard et al. 2002), polynuclear neutrophils (Mesri and Altieri 1999) or dendritic cells. After have been considered as cell dust, MPs are now considered to reflect cell activation. Platelet derived microparticles have been the most extensively studied until now. They are now accepted to play an important role in the procoagulant... 

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