Protein conversion factor role

The essential and most thoroughly defined role of vitamin K is as a cofactor to vitamin K-dependent carboxylase, an enzyme necessary for the posttranslational conversion of specific glutamyl residues in target proteins to y-carboxygiutamyl (Gla) residues. This y-carboxylation increases the affinity of these proteins for calcium. The antihemorrhagic function of vitamin K depends upon the formation of the Gla proteins prothrombin (factor II), proconvertin (factor VII), plasma thromboplastin component (factor IX), and Stuart factor (factor X), which together with two other hemostatic vitamin K-dependent proteins, proteins C and S and Ca A initiate a process to form... 

Antifibrinolytic compounds can block the conversion of plasminogen to plasmin, or directly bind to the active site of plasmin to inhibit fibrinolysis. The plasma protein, a 2-macroglobulin, is a primary physiological inhibitor of plasmin. Plasmin released from fibrin is also very rapidly inactivated by a2-antiplasmin, which plays a role in the regulation of the fibrinolytic process (Aoki and Harpel, 1984). 2-anti plasmin inactivates plasmin in a very rapid reaction, interferes with plasminogen binding to fibrin, and is ligated to fibrin by Factor Xllla (Sakata and Aoki, 1980). After a2-antiplasmin is covalendy linked to fibrin s G-terminal a chain, it retains it ability to inhibit plasmin, a function that helps to prevent premature clot lysis. 

The role of soluble protein factor in chloroplast electron transport. In Non-Heme Iron Proteins Role in Energy Conversion, A. San Pietro, ed., Antioch Press, Yellow Springs, Ohio, pp. 115—136 (1965). 

Finally, the common pathway involves thrombin in a number of functions. Its primary role is the conversion of fibrinogen to fibrin, the building block of a haemostatic plug. In addition, it activates factors VIII and V and their inhibitor protein C (in the presence of thrombomoduhn), and it activates factor XIII, which cross-links the fibrin polymers. 

The liver synthesizes fibrinogen factors V, VIII, XI, and XII, and the vitamin K-dependent factors II, VII, IX, and X. Furthermore the liver plays an important role in platelet growth and function. The vitamin K-dependent proteins contain y-carboxy-glutamic acid. Vitamin K is necessary for the carboxylation of these proteins, which facilitate the conversion of prothrombin to thrombin. Patients with severe hepatocellular disease have decreased synthesis of the vitamin K-dependent clotting factors, especially factor VII. Furthermore, patients with cholestatic disease have decreased bile salt secretion, which is necessary for the absorption of vitamin K, leading to failure of activation of factors II, VII, IX, and X. In these patients, unlike those with hepatocellular disease, the prothrombin time can be corrected with an injection of vitamin K. 

The role of the cytoplasmic effectors is obscure since their effects disappear when the enzyme is solubilized by Triton X-100. The possible participation of the soluble protein factor (SPF) as a carrier for substrate inside the membrane has been explored (Chapter 3). The SPF has been shown not only to stimulate the conversion of externally added squalene and oxidosqualene but also to activate squalene epoxidase as well as 2,3-oxidosqualene cyclase when the substrate is membrane bound [85,86]. SPF has been purified and shown to promote the transfer of squalene from one population of microsomes to another [87,88]. Nevertheless, SPF has no... 

Cell adhesion molecules (CAMs) are transmembrane glycoproteins that act at the cell surface to mediate specific binding interactions with other cell adhesion molecules on adjacent cells or with proteins in the extracellular matrix. They are responsible for the adhesion of various leukocytes with each other, with extracellular matrix and with other cell types. There are four families of CAMs that facilitate these interactions. The classification is based on differences in struchue and includes selectins, cadherins, integrins, and immunoglobulin superfamily (Table 9). CAMs play a role in renal morphogenesis and are expressed in the adult human kidney. These molecules can influence growth factor expression, and conversely growth factors can modulate production of cell surface adhesion molecules and the expression of extracellular matrix proteins. 

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