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951.
Giuseppe Inesi 《Cell biochemistry and biophysics》1987,11(1):269-277
The coupling mechanism of sarcoplasmic reticulum ATPase is based on the reciprocal influence of calcium binding and phosphorylation
domains. Cooperative calcium binding activates the enzyme, permitting utilization of ATP by transfer of its terminal phosphate
to the enzyme. Occupancy of the phosphorylation domain then produces internalization and dissociation of the bound calcium.
Hydrolytic cleavage of Pi completes the catalytic and transport cycle. Conversely, the phosphorylated enzyme intermediate can be formed with Pi in the absence of Ca2+. This intermediate is then destabilized by calcium binding, permitting formation of ATP by phosphoryl transfer to ADP. 相似文献
952.
The binding of various nucleotides to chloroplast coupling factor CF1 was studied by two dialysis techniques. It was found that the number of nucleoside diphosphate sites and their specificities for the base moiety is dependent on the magnesium concentration. In the presence of 50 μM added MgCl2, the protein has a single strong site/mol protein with Kd = 0.5 μM for ADP and high specificity (Kd > 20 μM for ?ADP, GDP, CDP). In the presence of 5 mM MgCl2, the protein has two independent tight ADP sites (Kd = 0.4 μM) of low specificity (Kd ≈ 0.8, 2, and 2 μrmM, respectively for ?ADP, GDP, and CDP). These results are compared with the specificity of the partial reactions for photophosphorylation. 相似文献
953.
S Ohta M Nakanishi M Tsuboi M Yoshida Y Kagawa 《Biochemical and biophysical research communications》1978,80(4):929-935
The kinetics of the hydrogen-deuterium exchange reaction in a stable ATPase (TF1) from a thermophilic bacterium PS3 was followed by infrared absorption measurements. The rates of the hydrogen-deuterium exchange reactions decreased in following order; free form, TF1·ADP, TF1·ATP and TF1·AMP-P(NH)P. TF1 does not dissociate into subunits even in the absence of nucleotides, thus differences in exchange likely reflect differences in conformations of subunits. These results indicate that the structure is most restricted when ATP or AMP-P(NH)P is bound to the enzyme. 相似文献
954.
The interaction of tentoxin with solubilized lettuce chloroplast coupling factor 1 was characterized by direct binding studies, measurement of the time course of ATPase inhibition, and steady-state enzyme kinetics. Neither substrates, products or Ca2+ competed with the tentoxin binding site, nor did they induce any large change in tentoxin affinity. The inhibition of lettuce chloroplast coupling factor 1 ATPase was found to be the time dependent, and at equilibrium the affinities estimated by equilibrium ultrafiltration and enzyme inhibition were similar (1.8 · 108M?1). The steady-state kinetics best fit an uncompetitive pattern suggesting that the inhibited steps follow an irreversible step occurring after ATP binding. 相似文献
955.
956.
A method of formylation of peptides using formic acid and isovaleroyl chloride is outlined in this communication. Its application for synthesis of several model peptides is also presented. 相似文献
957.
Intense illumination of isolated, intact, spinach chloroplasts triggers the well known proton-pumping Mg2+ ATPase activity of coupling factor, which can be assayed in subsequently lysed chloroplasts by monitoring ATP-driven quenching of 9-aminoacridine fluorescence. The light-triggered ATPase activity decays slowly in the dark and is inhibited by N,N′-dicyclohexylcarbodiimide. After osmotic lysis and washing of the chloroplasts, preillumination no longer triggers maximal proton-pumping ATPase until methylviologen and dithiothreitol are added to the medium. It is suggested that intact organelles contain soluble or loosely bound cofactors necessary for light-triggering of coupling factor ATPase. On osmotic lysis, these endogenous cofactors are diluted or inactivated and must be replaced by addition of a dithiol reagent and an electron acceptor. 相似文献
958.
(1) Photophosphorylation, fCa2+-ATPase and Mg2+-ATPase activities of isolated chloroplasts were inhibited 55–65% when the chemical potential of water was decreased by dehydrating leaves to water potentials (ψw) of ?25 bars before isolation of the plastids. The inhibition could be reversed in vivo by rehydrating the leaves.(2) These losses in activity were reflected in coupling factor (CF1) isolated from the leaves, since CF1 from leaves with low ?w had less Ca2+-ATPase activity than control CF1 and did not recouple phosphorylation in CF1-deficient chloroplasts. In contrast, CF1 from leaves having high ?w only partially recoupled phosphorylation by CF1-deficient chloroplasts from leaves having low ?w. This indicated that low ?w affected chloroplast membranes as well as CF1 itself.(3) Coupling factor from leaves having low ψw had the same number of subunits, and the same electrophoretic mobility, and could be obtained with the same yields as CF1 from control leaves. However, direct measurements of fluorescence polarization, ultraviolet absorption, and circular dichroism showed that CF1 from leaves having low ?w differed from control CF1. The CF1 from leaves having low ?w also had decreased ability to bind fluorescent nucleotides (?-ATP and ?-ADP).(4) Exposure of isolated CF1 to low ?w in vitro by preincubation in sucrose-containing media inhibited the Ca2+-ATPase activity of the protein in subsequent assays without sucrose. Inclusion of 5 or 10 mM Mg2+ in the preincubation medium markedly inhibited Ca2+-ATPase activity.(5) These results show that CF1 undergoes changes in cells which alter its phosphorylating ability. Since low cell ?w changed the spectroscopic properties but not other protein properties of CF1, the changes were most likely caused by altered conformation of the protein. This decreased the binding of nucleotides and, in turn, photophosphorylation. The inhibition of ATPase activity in CF1 in vitro at low ?w and high ion concentration mimicked the change in activity seen in vivo. 相似文献
959.
960.
Pellerin L 《Molecular neurobiology》2005,32(1):59-72
For years glucose was thought to constitute the sole energy substrate for neurons; it was believed to be directly provided
to neurons via the extracellular space by the cerebral circulation. It was recently proposed that in addition to glucose,
neurons might rely on lactate to sustain their activity. Therefore, it was demonstrated that lactate is a preferred oxidative
substrate for neurons not only in vitro but also in vivo. Moreover, the presence of specific monocarboxylate transporters
on neurons as well as on astrocytes is consistent with the hypothesis of a transfer of lactate from astrocytes to neurons.
Evidence has been provided for a mechanism whereby astrocytes respond to glutamatergic activity by enhancing their glycolytic
activity, resulting in increased lactate release. This is accomplished via the uptake of glutamate by glial glutamate transporters,
leading to activation of the Na+/K+ ATPase and a stimulation of astrocytic glycolysis. Several recent observations obtained both in vitro and in vivo with different
approaches have reinforced this view of brain energetics. Such an understanding might be critically important, not only because
it forms the basis of some classical functional brain imaging techniques but also because several neurodegenerative diseases
exhibit diverse alterations in energy metabolism. 相似文献