Erythrocytes substrates

The human red blood cell (erythrocyte) has a shape of biconcave disc with minimal (D ) and maximal (D ) thickness and radius R (Fig. 10.1a). The optical scheme of a reflected microscope with deposited red blood cells is shown in Fig. 10. lb. The light scattering process takes place at the interface of three media air-erythrocyte-substrate with refractive index n, n and n respectively. Since the erythrocyte thickness is of the same order of magnitude as the wavelength of incidental light, the interference phenomena take place on these blood cells. The reflective capacity of an interface between two media with refractive indices n, and n is described by Eq. 10.1 [10] ... 

Figure 8. Effect of free arachidonic acid on the lipopooxidase activity of (I) non-selenic glutathione S-transferase from porcine liver and (2) Se-containing glutathione peroxidase from bovine erythrocytes (substrate - 15 mM 15-hydroperoxyarachidonic acid) [33].

Figure 21 -8 Major glycolytic pathways of the erythrocyte. Substrates are in uppercase type, and enzymes are in parentheses. EMP, The Embden-Meyerhof pathway HMP hexose monophosphate pathway or pentose shunt RLC, the Rapoport-Luebering cycle ADP, adenosine diphosphate ATP, adenosine triphosphate NAD, nicotinamide-adenine dinudeotide NADH, reduced nicotinamide-adenine dinucleotide NADP, nicotinamide-adenine dinucleotide phosphate NADPH, reduced nicotinamide-adenine dinucleotide phosphate.The step from ribulose-5-phosphate, which is shown as being catalyzed by transketolase and transaldolase, is an abbreviation of this portion of the HMR...

The gradients of H, Na, and other cations and anions established by ATPases and other energy sources can be used for secondary active transport of various substrates. The best-understood systems use Na or gradients to transport amino acids and sugars in certain cells. Many of these systems operate as symports, with the ion and the transported amino acid or sugar moving in the same direction (that is, into the cell). In antiport processes, the ion and the other transported species move in opposite directions. (For example, the anion transporter of erythrocytes is an antiport.) Proton symport proteins are used by E. coU and other bacteria to accumulate lactose, arabinose, ribose, and a variety of amino acids. E. coli also possesses Na -symport systems for melibiose as well as for glutamate and other amino acids. 

In erythrocytes, the pathway has a major function in preventing hemolysis by providing NADPH to maintain glutathione in the reduced state as the substrate for glutathione peroxidase. 

Murray, Jr., E. D. and Clarke, S., Synthetic peptide substrates for the erythrocyte protein carboxyl methyltransferase, J. Biol. Chem., 259, 10722, 1984. 

Zinc protoporphyrin IX is a normal metabolite that is formed in trace amounts during haem biosynthesis. However, in iron deficiency or in impaired iron utilization, zinc becomes an alternative substrate for ferrochelatase and elevated levels of zinc protoporphyrin IX, which has a known low affinity for oxygen, are formed. This zinc-for-iron substitution is one of the first biochemical responses to iron depletion, and erythrocyte zinc protoporphyrin is therefore a very sensitive index of bone-marrow iron status (Labbe et ah, 1999). In addition, zinc protoporphyrin may regulate haem catabolism by acting as a competitive inhibitor of haem oxygenase, the key enzyme of the haem degradation pathway. However, it has been reported... 

Smith (1996) summarized data on the spontaneous methemoglobin reductase activity of mammalian erythrocytes. Using nitrated RBCs with glucose as a substrate, the data reflect the ratio of the activity of the species to the activity in human RBCs. Activity in rat cells and human cells ranged from 1.3 to 5.0. Activity in cells of the cat and dog was similar to that in human cells, and that of the rabbit was 3.3 to 7.5 times greater. Most studies show that the spontaneous methemoglobin reductase activity of human erythrocytes is within an order of magnitude of that of other mammals (Smith 1996). 

To investigate these two questions, a parametric model of the Jacobian of human erythrocytes was constructed, based on the earlier explicit kinetic model of Schuster and Holzhiitter [119]. The model consists of 30 metabolites and 31 reactions, thus representing a metabolic network of reasonable complexity. Parameters and intervals were defined as described in Section VIII, with approximately 90 saturation parameters encoding the (unknown) dependencies on substrates and products and 10 additional saturation parameters encoding the (unknown) allosteric regulation. The metabolic state is described by the concentration and fluxes given in Ref. [119] for standard conditions and is consistent with thermodynamic constraints. 

This flattened erythrocyte preparation has been used to study reversible nonspecific adsorption kinetics and surface diffusion of insulin on the external surface of erythrocytes.(123) The nonspecific adsorption of insulin to the polylysine-coated substrate is very large compared to the adsorption to the flattened membrane adhered to the substrate. Fortunately, this nonspecific background fluorescence can be very successfully quenched simply by preparing the polylysine coating on an aluminum-film-coated glass surface, rather than on bare glass. As discussed in Section 7.3, the aluminum abolishes the fluorescence of fluorophores adsorbed directly onto the polylysine substrate, but the fluorophores adsorbed to the erythrocyte surface are not substantially quenched, because they are spaced at least two membrane thicknesses away. 

The NADPH is produced from glucose 6-phosphate in the first three reactions in the pentose phosphate pathway (see below). Hence the pentose phosphate pathway is essential in the erythrocyte and glycolysis provides the substrate glucose 6-phosphate. Individuals with a reduced amount of glucose 6-phosphate dehydrogenase can suffer from oxidative damage to their cells and hence haemolysis. 

Nucleoside phosphorylases that catalyse the reversible cleavage of purine nucleosides to the free bases and ribose-1-phosphate are found in most cells, although a phosphorylase that will cleave adenosine has so far been identified only in bacteria. Recent studies have shown that ribo- and 2 -deoxyribofurano-syltransferase activity is associated with phosphorylase activity [19, 23., 222] and that both activities reside in one enzyme, which can be converted from one form to the other by substrate or product binding [20]. Upon crystallization of the enzyme from human erythrocytes a marked decrease in the ribosyl transfer reaction was observed [21b]. 

Chronic in vivo hemolysis produces serum lactic dehydrogenase elevations in patients with mitral or atrial valve cardiac prosthesis (J2). In a series of 11 such patients these increases ranged from 1.1 to 1.6 times the upper limit of normal (S29). Blood pH is altered in hemolyzcd specimens because carbonic anhydrase is liberated from the erythrocytes and presumably alters the distribution of H2CO3 and NaHCOs (B2). Hemolysis will effect acid phosphatase activity if the substrate is hydrolyzed by erythrocyte acid phosphatase. Thus, hemolysis would be of concern if phenyl phosphate was the substrate, but would have a negligible effect if )8-glycerophosphate, which is not hydrolyzed by red cell acid phosphatase, was used (Bl). 

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