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Query: EC:3.6.3.1 (Mg2+-ATPase)
 1,484 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

(1) Photophosphorylation, Ca2+-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 (psi w) 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 psi 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 psi w only partially recoupled phosphorylation by CF1-deficient chloroplasts from leaves havig low psi w. This indicated that low psi w affected chloroplast membranes as well as CF1 itself. (3) Coupling factor from leaves having low psi w 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 psi w differed from control CF1. The CF1 from leaves having low psi w also had decreased ability to bind fluorescent nucleotides (epsilon-ATP and epsilon-ADP). (4) Exposure of isolated CF1 to low psi 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 psi w changed the spectroscopic properties but not other protein properties of CF1, the changes were most likely caused by altered confurn, photophosphorylation. The inhibition of ATPase activity in CF1 in vitro at low psi w and high ion concentration mimicked the change in activity seen in vivo.
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PMID:Conformation and activity of chloroplast coupling factor exposed to low chemical potential of water in cells. 15 20

Photophosphorylating activity of chloroplasts rapidly prepared from preilluminated spinach leaves was higher than the activity of chlorplasts from leaves kept in the dark. Higher Vmax values were obtained with the former when either ADP or Pi concentrations were varied. The rate of decay of the in vivo light-activated Mg2+-ATPase was highly dependent on temperature, increasing with it. At 0 degree C it was stable for 40 min or more. The decay at 25 degrees C was prevented by 5 mM ATP or 50 mM dithioerythritol while ADP or Pi did not affect it. Gramicidin or iodosobenzoate induced a very rapid decay even at 0 degree C. Coupling factor 1 with a manifest and stable Ca2+-ATPase activity was solubilized from chloroplasts activated by light in vivo. Incubation of chloroplasts from preilluminated leaves with N-[3H]ethylmaleimide resulted in an inhibition of Ca2+-ATPase activity and in the incorporation of radioactivity into the gamma subunit of coupling factor 1 that was larger than that of chloroplasts from leaves kept in the dark. The results show that activation in vivo of the proton ATPase was manifested by higher phosphorylating and Mg2+-ATPase activities and requires both an electrochemical proton gradient and a redox change of at least one disulfide bond of its gamma subunit.
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PMID:Changes in activity and structure of the chloroplast proton ATPase induced by illumination of spinach leaves. 622 27

6alpha,7beta-Dihydroxyvouacapan-17beta-oic acid (1) was isolated from Pterodon polygalaeflorus Benth. Modification of 1 yielded 6alpha-hydroxyvouacapan-7beta,17beta-lactone (2) and then 6-oxovouacapan-7beta,17beta-lactone (3). Photosynthesis inhibition by 3 was evaluated in spinach chloroplasts. The uncoupled non-cyclic electron transport rate and ATP synthesis were inhibited by 3, which behaved as a Hill reaction inhibitor. Furthermore, 3 acted as an uncoupler because it enhanced the basal and phosphorylating electron transport rate on thylakoids. This last property of 3 was corroborated when it was observed that it enhances the Mg2+-ATPase activity. In contrast, 3 did not affect photosystem I (PSI) activity. Analysis of the partial photosystem II (PSII) reactions from water to DCPIPOX and water to silicomolybdate allowed to locate the inhibition sites at the redox components of PSII. The OJIP test of the chlorophyll a fluorescence transient confirmed that the inhibition sites were 1.) the oxygen-evolving complex (OEC) and 2.) by the formation of silent centers in the non-QA reducing centers.
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PMID:A diterpene gamma-lactone derivative from Pterodon polygalaeflorus Benth. as a photosystem II inhibitor and uncoupler of photosynthesis. 1672 81

Limited exposure of aminophospholipids on the outer leaflet of the plasma membrane is a fundamental feature of eukaryotic cells and is maintained by the action of inward-directed P-type ATPases ("flippases"). Yeast S. cerevisiae has five flippases (Dnf1, Dnf2, Dnf3, Drs2, and Neo1), but their regulation is poorly understood. Two paralogous plasma membrane-associated protein kinases, Pkh1 and Pkh2 (orthologs of mammalian PDK1), are required for viability of S. cerevisiae cells because they activate several essential downstream protein kinases by phosphorylating a critical Thr in their activation loops. Two such targets are related protein kinases Ypk1 and Ypk2 (orthologs of mammalian SGK1), which have been implicated in multiple processes, including endocytosis and coupling of membrane expansion to cell wall remodeling, but the downstream effector(s) of these kinases have been elusive. Here we show that a physiologically relevant substrate of Ypk1 is another protein kinase, Fpk1, a known flippase activator. We show that Ypk1 phosphorylates and thereby down-regulates Fpk1, and further that a complex sphingolipid counteracts the down-regulation of Fpk1 by Ypk1. Our findings delineate a unique regulatory mechanism for imposing a balance between sphingolipid content and aminophospholipid asymmetry in eukaryotic plasma membranes.
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PMID:A protein kinase network regulates the function of aminophospholipid flippases. 1996 3