Erythrocytes membrane-bound

Diabetic patients have reduced antioxidant defences and suffer from an increased risk of free radical-mediated diseases such as coronary heart disease. EC has a pronounced insulin-like effect on erythrocyte membrane-bound acetylcholinesterase in type II diabetic patients (Rizvi and Zaid, 2001). Tea polyphenols were shown to possess anti-diabetic activity and to be effective both in the prevention and treatment of diabetes (Choi et al, 1998 Yang et al, 1999). The main mechanism by which tea polyphenols appear to lower serum glucose levels is via the inhibition of the activity of the starch digesting enzyme, amylase. Tea inhibits both salivary and intestinal amylase, so that starch is broken down more slowly and the rise in serum glucose is thus reduced. In addition, tea may affect the intestinal absorption of glucose. 

Kinetic changes of erythrocyte membrane-bound acetylcholinesterase from rats fed fat-free diet... 

Table 7. Hill coefficient and transition temperatures of erythrocyte membrane-bound enzymes from rats fed different lipid supplemented diets... 

Bettger, W.J. 1989. The effect of dietary zinc deficiency on erythrocyte-free and membrane-bound amino acids in the rat. Nutr. Res. 9 911-919. 

Fig. 2.4. Schematic model of the molecular polymorphism of acetylcholinesterase and cholinesterase [110][112a]. Open circles represent the globular (G) catalytic subunits. Disulfide bonds are indicated by S-S. The homomeric class exists as monomers (Gl), dimers (G2), and tetramers (G4) and can be subdivided into hydrophilic (water-soluble) and amphiphilic (membrane-bound) forms. The G2 amphiphilic forms of erythrocytes have a glycophospholipid anchor. The heteromeric class exists as amphiphilic G4 and as asymmetric forms (A) containing one to three tetramers. Thus, heteromeric G4 forms found in brain are anchored into a phospholipid membrane through a 20 kDa anchor. The asymmetric A12 forms have three hydrophilic G4 heads linked to a collagen tail via disulfide bonds.

In the absence of activators AMP aminohydrolase from brain (149), erythrocytes (143, 150), muscle (145), and liver (128) gave sigmoid curves for velocity vs. AMP concentration which were hyperbolic after the addition of monovalent cations, adenine nucleotides, or a combination of monovalent cations and adenine nucleotides. For the rabbit muscle enzyme (145), addition of K+, ADP, or ATP produced normal hyperbolic saturation curves for AMP as represented by a change in the Hill slope nH from 2.2 to 1.1 Fmax remained the same. The soluble erythrocyte enzyme and the calf brain enzyme required the presence of both monovalent cations and ATP before saturation curves became hyperbolic. In contrast, the bound human erythrocyte membrane enzyme did not exhibit sigmoid saturation curves and K+ activation was not affected by ATP (142). 

An alternative displacement method, reported by Nagao and coworkers (46,47), is based on a lengthy and more complex procedure. Sarin-bound acetylcholinesterase was solubilized from erythrocyte membranes, digested with trypsin (37 °C, 24 h), and the hydrolysis product isopropyl methylphos-phonic acid released by digestion with alkaline phosphatase (37 °C, 48 h). High molecular mass... 

This enzyme is considered to be important to maintenance of the proper level of calcium ion in the erythrocyte. As such it is also considered to be typical of a membrane-bound enzyme. Upon purification of this enzyme from human erythrocytes, it was found that the purified enzyme exhibited no activity until a mixture of a nonionic detergent and a charged phospholipid (e.g., phospha-tidylserine or phosphatidylinositol), were included in the assay system (Nelson and Hanahan, 1985). Ten- to twelvefold increases in activity could be achieved. If a neutral phospholipid such as phosphatidylcholine were substituted for the phosphatidylserine (or phosphatidylinositol), essentially there was little or no enzymatic activity. 

Catalase is an enzyme that is present in most aerobic cells of a wide variety of origins, and is located in most plant and animal cells in the single membrane-bounded organelles known as peroxisomes [1]. In human tissues there is a very high concentration of the enzyme in liver and erythrocytes, and there is relatively much less in brain, heart and skeletal muscle [3], The general reaction catalysed by the enzyme is ... 

It has been long recognized that a number of enzymes in a living cell are bound to the membraneous structures of the cell. For example, Green e t al. ( 1 ) described a pH-dependent binding of several glycolytic enzymes to the erythrocyte membranes and concluded that the entirety of the glycolytic system was associated with the membrane and is not free in solution. 

Because vitamin E is transported in lipoproteins secreted hy the liver, the plasma concentration depends to a great extent on total plasma lipids. Erythrocytes may also he important in transport, because there is a relatively large amount of the vitamin in erythrocyte membranes, and this is in rapid equilibrium with plasma vitamin E. There are two mechanisms for tissue uptake of the vitamin. Lipoprotein lipase releases the vitamin by hydrolyzing the tri-acylglycerol in chylomicrons and VLDL, whereas separately there is receptor-mediated uptake of LDL-bound vitamin E. Studies in knockout mice suggest that the main mechanism for tissue uptake of vitamin E from plasma lipoproteins is byway of the class B scavenger receptor (Mardones et al., 2002). 

Cytochrome exists in a soluble form in erythrocytes and in a membrane bound form in microsomes. A soluble derivative of hepatic cyt bs with 93 amino acids can be isolated by treatment of microsomes with pancreatic lipase and this form has essentially the same amino acid sequence as the erythrocyte protein. Further treatment of the soluble form with trypsin cleaves two residues from the N-terminal and seven from the carboxylate-terminal and leaves the heme core with only 84 residues. Rat liver cyt b has been prepared by expression in Eschericha coli (E.coli). The structure of... 

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