Nucleotide uptake

Nucleotide Uptake. When uracil labelled with tritium was supplied to 15-day-old ozone-treated cotton leaves, a 2-fold increase in uracil incorporation into the RNA fraction was observed (Table IV). In this one particular case, there appeared to be a greater percentage of uracil incorporation into RNA in treated tissue than in control tissue. 

A much slower transport process which catalyzes the net uptake of ATP has been demonstrated in liver [42,43] and heart mitochondria [44,45], and shown to be physiologically important in neonatal liver mitochondria [46,47]. The transporter s activity may be affected by hormones since it has been shown that glucagon treatment increases the total nucleotide content of subsequently isolated liver mitochondria [48]. Although initially thought to be due to rather nonspecific leakiness of mitochondrial membranes or unidirectional transport on the adenine nucleotide carrier, its lack of sensitivity to membrane potential, and its almost absolute dependence on the presence of Mg and phosphate suggest that the observed activity is due to a separate transporter [42]. Net nucleotide uptake in plant mitochondria is much more marked but has a similar dependence on Mg " and phosphate in the media [49]. 

Sanderson IR, He Y. Nucleotide uptake and metabolism by intestinal epithelial cells. J Nutr 1994 Jan 124(1 suppl) 131S-137S. 

The kinetic and binding parameters of the yeast transporter have been studied in some detail in our laboratory. Adenine nucleotide uptake has been studied in mitochondria isolated from cells grown anaerobically and aerobically under both catabolite repressed or derepressed conditions. The specific inhibitors, atractylate and bongkrekate, have been used to examine the number and nature of the adenine nucleotide binding sites present in the mitochondria of cells grown under the various conditions. Atractylate is a competitive inhibitor of the transporter, while bongkrekate increases the affinity of the transporter for adenine nucleotides so that subsequent dissociation is prevented and the flux of nucleotides across the membrane is inhibited. 

The physiological changes resulting from the different growth conditions did not significantly alter the kinetic and binding constants of adenine nucleotide uptake. In all cases the uptake was resolved into an atractylate-sensitive component which was specific for ADP or ATP, with a of 0.5 ixu (due to a typographical error, this K n value was reported as 5.0 /iM in Haslam et a/. ), and an atractylate-insensitive activity which was nonspecific and could not be saturated. 

We have recently reported that adenine nucleotide uptake of mitochondria prepared from a cytoplasmic petite strain and from cells grown in the presence of erythromycin was not sensitive to atractylate inhibition. It was inferred that a product of mitochondrial protein synthesis was required for atractylate sensitivity. Kolarov and Klingenberg have... 

Chemical modification studies with fluorescein-5 -isothiocyanate support the proximity of Lys515 to the ATP binding site [98,113-117,212,339]. Fluorescein-5 -isothiocyanate stoichiometrically reacts with the Ca -ATPase in intact or solubilized sarcoplasmic reticulum at a mildly alkaline pH, causing inhibition of ATPase activity, ATP-dependent Ca transport, and the phosphorylation of the Ca " -ATPase by ATP the Ca uptake energized by acetylphosphate, carbamylphos-phate or j -nitrophenyl phosphate is only partially inhibited [113,114,212,339]. The reaction of -ATPase with FITC is competitively inhibited by ATP, AMPPNP, TNP-ATP, and less effectively by ADP or ITP the concentrations of the various nucleotides required for protection are consistent with their affinities for the ATP binding site of the Ca -ATPase [114,212,340]. 

Five structural genes for amino acid uptake systems have been cloned in Saccharomyces cerevisiae by functional complementation, and their putative amino acid sequences deduced from the respective nucleotide sequences (Fig. 2). 

Female NMRI mice were exposed to 100 ppm of hydrogen sulfide for 2 hours at 4-day intervals excitement was observed (Savolainen et al. 1980). Exposure also resulted in decreased cerebral ribonucleic acid (RNA), decreased orotic acid incorporation into the RNA fraction, and inhibition of cytochrome oxidase. An increase in the glial enzyme marker, 2, 3 -cyclic nucleotide-3 -phosphohydrolase, was seen. Neurochemical effects have been reported in other studies. Decreased leucine uptake and acid proteinase activity in the brain were observed in mice exposed to 100 ppm hydrogen sulfide for 2 hours (Elovaara et al. 1978). Inhibition of brain cytochrome oxidase and a decrease in orotic acid uptake were observed in mice exposed to 100 ppm hydrogen sulfide for up to 4 days (Savolainen et al. 1980). 

Several different changes in mitochondria occur during apoptosis. These include a change in membrane potential (usually depolarization), increased production of reactive oxygen species, potassium channel activation, calcium ion uptake, increased membrane permeability and release of cytochrome c and apoptosis inducing factor (AIF) [25]. Increased permeability of the mitochondrial membranes is a pivotal event in apoptosis and appears to result from the formation of pores in the membrane the proteins that form such permeability transition pores (PTP) may include a voltage-dependent anion channel (VDAC), the adenine nucleotide translocator, cyclophilin D, the peripheral benzodiazepine receptor, hexokinase and... 

Several of the proteins that mediate Ca2+ flow in and out of SR have been identified. Oxalate-facilitated Ca2+ uptake into the SR and in vitro biochemical studies of purified SR identified it as an ATP-driven Ca2+ pump (SERCA pump reviewed in Himpens et al 1995) that is inhibited by thapsigargin and cyclopiazonic acid and regulated, at least in some smooth muscles, by phosphorylation of phospholamban by cyclic nucleotide-activated protein kinase(s) (Karczewski et al 1998). 

Al. Anderson, E. P., Kalckar, H. M., and Isselbacher, K. J., Defect in uptake of galactose-l-phosphate into liver nucleotides in congenital galactosemia. Science 125, 113-114 (1957). 

Many experimental variations are possible when performing uptake studies [246]. In a simple experiment for which the cells are initially free of internalised compound, the initial rates of transmembrane transport may be determined as a function of the bulk solution concentrations. In such an experiment, hydrophilic compounds, such as sugars, amino acids, nucleotides, organic bases and trace metals including Cd, Cu, Fe, Mn, and Zn [260-262] have been observed to follow a saturable uptake kinetics that is consistent with a transport process mediated by the formation and translocation of a membrane imbedded complex (cf. Pb uptake, Figure 6 Mn uptake, Figure 7a). Saturable kinetics is in contrast to what would be expected for a simple diffusion-mediated process (Section 6.1.1). Note, however, that although such observations are consistent... 

Sayavedra-Soto, L. A., Powell, G. K., Evans, H. J. and Morris, R. O. (1988) Nucleotide sequence of the genetic loci encoding subunits of Bradyrhizobium japonicum uptake hydrogenase. Proc. Natl. Acad. Sci. USA, 85, 8395-9. 

Nozawa, T., Minami, H., Sugiura, S., Tsuji, A., and Tamai, 1. (2005) Role of organic anion transporter OATPIBI (OATP-C) in hepatic uptake of irinotecan and its active metabolite, 7-ethyl-10-hydroxycamptothecin in vitro evidence and effect of single nucleotide polymorphisms. Drug Metab. Dispos. 33, 434—439. 

Vanttinen, M., Nuutila, P., Kuulasmaa, T., et al. (2005) Single nucleotide polymorphisms in the peroxisome proUferator-activated receptor delta gene are associated with skeletal muscle glucose uptake. Diabetes. 54,3587-3591. 

Figure 8.29 The initial reactions of glutamine metabolism in kidney, intestine and cells of the immune system. The initial reaction in all these tissues is the same, glutamine conversion to glutamate catalysed by glutaminase the next reactions are different depending on the function of the tissue or organ. In the kidney, glutamate dehydrogenase produces ammonia to buffer protons. In the intestine, the transamination produces alanine for release and then uptake and formation of glucose in the liver. In the immune cells, transamination produces aspartate which is essential for synthesis of pyrimidine nucleotides required for DNA synthesis otherwise it is released into the blood to be removed by the enterocytes in the small intestine or by cells in the liver.

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