Calcium-binding sites glutamate residues

Annexins isolated from chondroblast matrix vesicles may be reconstituted with phospholipids to form calcium ion channels in the complete absence of Ca2+ ions. Indeed, annexin V has domains that directly bind calcium ions glutamate and aspartate residues provide the ion binding site (EF-hand domains). Figure 9.6b illustrates putative annexin V channels that mediate an influx of Ca2+ ions into artificial bilayers and liposomes (detectable with a calcium-sensitive fluorescent dye). These in vitro annexin Ca2+ channels, and also the Ca2+ influx into matrix vesicles in cell culture and in vivo, are blocked by Zn2+ ions, or a derivative of 1,4-benzothiazepine (inhibitor K201). 

Warfarin (Coumadin ) is a slow-and long-acting blood anticoagulant with a structure resembling that of vitamin K. The structural similarity allows the compound to compete with vitamin K and prevent -y-carboxylation of glutamate residues in Factors II, VII, IX, X, and proteins C and S. The noncarboxylated blood clotting protein precursors increase in both the blood and plasma, but they are unable to promote blood coagulation because they cannot bind calcium and thus cannot bind to their phospholipid membrane sites of activation. 

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