Glutamine translocation

The mutation of ThrlSl, Glyl82, or Glul83 to alanine, or of Glul83 to glutamine also completely inhibited the ATP or acetylphosphate-dependent Ca transport, without effect on the phosphorylation of the enzyme by ATP in the presence of Ca or by Pi in the absence of Ca [127]. The phosphoenzyme formed from ATP retained its ADP-sensitivity at low concentration and alkaline pH, but its rate of decomposition was much slower than that of the wild-type enzyme in the presence of EGTA. These observations implicate the 181-183 region in the conformational changes related to Ca translocation. 

The two important fuels for colonocytes are glutamine and short-chain fatty acids. The oxidation of both fuels provides ATP for the cells, which is important not only to maintain digestive and absorptive functions but also to maintain membrane structure and hence the physical barrier between the lumen and the blood and peritoneal cavity. This barrier normally prevents significant rates of translocation of bacteria into the peritoneal cavity and thence into the blood. If this barrier is breached, translocation of pathogens and... 

The mitochondrial translocators which have been most carefully assessed with respect to their role in control of metabolism are (1) the adenine nucleotide translocator with respect to its role in the control of respiration (2) the liver pyruvate transporter and the control of gluconeogenesis and (3) kidney glutamate and glutamine transport and their control of ammoniagenesis. 

ABC transporters translocate many different allocrites (transport substrates), but the primary structures of the NBDs show --25% sequence identity across the whole superfamily [9[. Marked sequence conservation is observed over five short regions found in the NBDs (i) the Walker A and (ii) Walker B regions, which are separated by approximately 90-120 amino acids and between which lie the (hi) signature motif [2, 7, 9, 35, 36] and (iv) the glutamine loop (Q-loop) [37[. The most C-terminal motif is the histidine loop (H-loop) [2[. The signature, Q-loop, and H-loop seem to be specific to ABC transporters [9], and the function of these is described in more detail below. A recent description of the importance of a highly conserved aromatic residue has led to the naming of an A-loop at the N-terminus of the NBD [38[. 

Table 2 Effect of mutating Escherichia coli GPATase tunnel residues on the efficiency of ammonia translocation and glutamine binding...

Enzyme Glutaminase activity (U mg ) Translocation efficiency Glutamine Kq (mmol I )... 

GFAT is unusual among amidotransferases in being unable to use ammonia as an alternate nitrogen source under in vitro conditions, precluding any direct assessment of the ability of glutamine to suppress ammonia-dependent synthase activity. The process of ammonia translocation has therefore been studied by steered MD simulations on a model of the active enzyme built from the crystal structure of the DON-modified form of... 

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