Membrane-bound kinetics

The steady-state balance of the Ca pump and plasma membrane leaks of Ca determines the resting intracellular free Ca concentration. Kinetically, all the other membrane bound compartments and their transport processes are analogous to buffer systems with various rates of binding and release. The essential point is that all the other pools must come to steady-state with the intracellular free concentration. Thus, the plasma membrane Ca -pump for the Ca economy of the cell has primacy. 

Chiu, TH, Dryden, DM and Rosenberg, HC (1982) Kinetics of [ H]-labelled flunitrazepam binding to membrane-bound benzodiazepine receptors. Mol. Pharmacol. 21 57-65. 

Cabanes J, Escribano J, Gandia-Herrero F, Garcia-Carmona F nd Jimenez-Atienzar M. 2007. Partial purification of latent polyphenol oxidase from peach (Prumis persica L. Cv. Catherina). Molecular properties and kinetic characterization of soluble and membrane-bound forms. J Agric Food Chem 55(25) 10446-10451. 

Brederode ME, Jones MR, Van Grondelle R (1997) Primary electron transfer kinetics in membrane-bound Rhodobacter sphaeroides reaction centers a global and target analysis. 

An important question arises about the effects of phospholipid composition and the function of membrane-bound enzymes. The phospholipid composition and cholesterol content in cell membranes of cultured cells can be modified, either by supplementing the medium with specific lipids or by incubation with different types of liposomes. Direct effects of phospholipid structure have been observed on the activity of the Ca2+-ATPase (due to changes in the phosphorylation and nucleotide binding domains) [37]. Evidence of a relationship between lipid structure and membrane functions also comes from studies with the insulin receptor [38]. Lipid alteration had no influence on insulin binding, but modified the kinetics of receptor autophosphorylation. 

Dunn SMJ, Blanchard SG, Raftery MA. 1980. Kinetics of carbamoylcholine binding to membrane-bound acetylcholine receptor monitored by fluorescence changes of a covalently bound probe. Biochemistry 19 5645-5652. 

Griinhagen HH, Iwatsubo M, Changeux JP. 1977. Fast kinetic studies on the interaction of cholinergic agonists with the membrane-bound acetylcholine receptor from Torpedo marmorata as revealed by quinacrine fluorescence. Fur J Biochem 80 225-242. 

Measurement of the rates of dissociation of enzyme-substrate and protein-ligand complexes, usually promoted by dilution. The utility of dissociation kinetics is well illustrated in the report of Dunn and Raftery who examined the kinetics of pH]acetylcholine and [ H]sub-eryldicholine dissociation from the membrane-bound... 

Regulatory enzymes containing multiple polypeptide chains are just beginning to be understood in molecular terms. Considerably more thermodynamic, kinetic, and structural information is required. Several multienzyme complexes are available in a reasonably pure state, but the molecular characterization of their mechanisms is still in a rather primitive state. The situation is even more difficult with membrane-bound enzymes. A few of these enzymes can be obtained as well-defined entities, but in many cases purification of the enzyme system and all its components is quite far off in the future. The small quantity of material usually available is also a great problem with these systems. As might be... 

The four forms of hexokinase found in mammalian tissues are but one example of a common biological situation the same reaction catalyzed by two or more different molecular forms of an enzyme. These multiple forms, called isozymes or isoenzymes, may occur in the same species, in the same tissue, or even in the same cell. The different forms of the enzyme generally differ in kinetic or regulatory properties, in the cofactor they use (NADH or NADPH for dehydrogenase isozymes, for example), or in their subcellular distribution (soluble or membrane-bound). Isozymes may have similar, but not identical, amino acid sequences, and in many cases they clearly share a common evolutionary origin. 

Thus, there is likely as many as three enzymes with 5 -nucleotidase activity in liver, one lysosomal, one cytoplasmic, and one membrane bound. Their specificities and kinetic properties appear to be distinctly different. This would suggest specialized physiological functions not yet understood. 

Many of the reactions of the plastocyanins and azurins with other redox proteins follow Marcus behaviour.946 These reactions all show a single mechanism of electron transfer, with no kinetic selectivity and no specific interactions between the proteins. The notable exception to this behaviour is cytochrome / (c552), where a specific interaction occurs,934 appropriate for its natural redox partner. Equation (48) represents a probable sequence of electron carriers, although it is difficult to extrapolate conclusions to the membrane-bound proteins. 

A measurement system that is able to quantitatively determine the interactions of receptor and G protein has the potential for more detailed testing of ternary complex models. The soluble receptor systems, ([l AR and FPR) described in Section II, allow for the direct and quantitative evaluation of receptor and G protein interactions (Simons et al, 2003, 2004). Soluble receptors allow access to both the extracellular ligandbinding site and the intracellular G protein-binding site of the receptor. As the site densities on the particles are typically lower than those that support rebinding (Goldstein et al, 1989), simple three-dimensional concentrations are appropriate for the components. Thus, by applying molar units for all the reaction components in the definitions listed in Fig. 2A, the units for the equilibrium dissociation constants are molar, not moles per square meter as for membrane-bound receptor interactions. These assemblies are also suitable for kinetic analysis of ternary complex disassembly. 

Multiple forms of GST have been demonstrated in the liver of many mammalian species multiple forms also occur in insects. Most GSTs are soluble dimeric proteins with molecular weights ranging between 45,000 and 50,000 daltons. All forms appear to be nonspecific with respect to the reaction types described, although the kinetic constants for particular substrates vary from one form to another. They are usually named from their chromatographic behavior. At least two are membrane-bound glutathione transferases, one of which is involved in metabolism of xenobiotics and is designated... 

Solymoss S, Tucker MM, Tracy PB. Kinetics of inactivation of membrane-bound factor V by activated protein C. J Biol Chem 1988 263 14,884-14,890. 

Kinetic analyses of the membrane-bound alkaline phosphatase activity of Hymenolepis diminuta (Cestoda Cyclophyllidea) in relation to development of the tapeworm in the definitive host. Journal of Cellular Biochemistry, 25 131-7. 

Abou-Rebeyeh, H., Korber, F., Schubert-Rehberg, K., Reusch, J., and Josic, D. (1991). Carrier membrane as a stationery phase for affinity chromatography and kinetic studies of membrane-bound enzymes.. Chromatogr. 566, 341-350. 

Even though water-soluble Se-GPx reduces a number of hydrophobic substrates [215,225], it does not directly reduce phospholipid hydroperoxides [226], Such a reduction would require the release of free fatty-acid hydroperoxides through activation of phospholipase A2 [227,228], More importantly, a membrane-bound Se-GPx has been found in a number of animal tissues, including liver, heart, brain and testis [229]. In vitro, this enzyme does reduce phospholipid hydroperoxides in micelles and exhibits kinetic features which, in the presence of detergent, are similar to those of the soluble enzyme (reviewed in ref. [230]). This enzyme which has been named PHGPx, also reduces hydroperoxide derivatives of cholesterol and that formed... 

Today 11 members of the human PDE superfamily are known, all of which are class I phosphodiesterases and all of which are intracellular or membrane-bound enzymes. Several of the isoenzymes are encoded by more than one gene which, in combination with the presence of different splice variants, brings the number of different PDE proteins to well over 50. The different isoenzymes are characterized according to their substrate specificity, sequence homology, kinetic properties, and sensitivity to certain known PDE inhibitors. Table 9.1 shows these properties together with the predominant tissue expression of the various PDEs. 

Van Stokkum, I. H. M., Beekman, L. M. P., Jones, M. R., Van Brederode, M. E., and Van Grondelle, R., 1997, Primary electron transfer kinetics in membrane-bound Rhodobacter sphaeroides reaction centers A global and target analysis. Biochemistry, 36 11360n 11368. 

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