ATPases excretion function

It is about an active mechanism depending on the Na+-K+-ATPase enzyme located in the lateral plasma membrane of the endothelial cells. It enables the penetration of potassium into the cell against the excretion of sodium into the aqueous humor. Then this latter becomes hypertonic in comparison with the stroma and thus drains the water. In normal conditions, the pump can adapt to the physiological needs. Actually, the moves of the sodium ion are relative to those of the bicarbonate ion (responsible for the negative polarization of the back side of the endothelial cell) and to the pH variation. And yet, the bicarbonate comes from the aqueous humor and from the intracellular transformation of carbon dioxide and water by carbonic anhydrase. All of this shows the good functioning of the pumps depends on the integrity of the plasma... 

Wilson s disease is a pathological accumulation of copper in tissue which is later released into the bloodstream, leading to anaemia, and final accumulation of copper in liver and brain. It is the result of a mutation in the Wilson s disease gene in chromosome 13 which ordinarily codes for a cation transporting ATPase so that copper can be incorporated into ceruloplasmin prior to excretion. Also known as ferroxi-dase, in acknowledgement of its primary function as an oxidoreductase responsible for electron transfer, this enzyme contains iron and, more importantly, six copper atoms. It accounts for the transport of 90% of copper in the plasma so any impairment in its production or efficacy has a major impact on copper homeostasis. The greatly reduced concentration of ceruloplasmin in the blood of Wilson s disease sufferers correlates with their inability to metabolize copper effectively. It leads to chronic liver disease, for which the only real cure is a liver transplant,... 

Copper The daily intake from food is 0.8—2.0 mg it is released into the portal vein via copper-transporting ATPase. The transport of copper, which is toxic in its free form, is effected by the binding to ceruloplasmin, albumin and transcuprin. Copper is bound to reduced glutathione and metallothionein in the hepatocytes and distributed to various organelles or incorporated into enzymes. The biological effects of copper are manifold and essential for some cellular functions, (s. p. 50) Copper is toxic not only in its free form, but also in cases of overload (e. g. cirrhosis in childhood due to the consumption of water from copper pipes). Copper homoe-ostasis is regulated via biliary excretion (normal value about 1.2-2.0 mg/day), so that the normal value in serum is 75-130 fg/dl. (321, 323, 370, 383, 386) (s. p. 102)... 

The answer is b. (Murray, pp 505-626. Scriver, pp 4029-4240. Sack, pp 121—138. Wilson, pp 287-320.) Calcium ions and calcium deposits are virtually universal in the structure and function of living things. In humans, calcium ions are required lor the activity of many enzymes. Calcium is taken up Irom the gut in the presence ol lorms of vitamin D, such as cholecalciferol. Calcium is also primarily excreted through the intestine. When soluble, it is present as a divalent cation. When insoluble, it is found as hydroxyapatite (calcium phosphate) in bone. It is required by muscle cells for contraction and is sequestered into the sarcoplasmic reticulum during relaxation. It is actively transported by a calcium-ATPase across the sarcoplasmic reticulum. 

There is good evidence that the calcium-transporting ATPase can be used as a marker enzyme for the plasma membrane of Anabaena. So far, only a transport function but no substantial electron transport function can be attributed to this membrane, unlike findings with Anacystis (Peschek et al. 1983) In vivo the calcium pump probably excretes calcium from the cell, since calcium is transported away from the side of ATP hydrolysis (into the isolated vesiclesX. 

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