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'H + ATPase' in keywords Facet   Publication Year 1981  [X]
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1Author    A. Hager, M. H. Elm LeRequires cookie*
 Title    Properties of an ATP-Fueled, Cl~-Dependent Proton Pump Localized in Membranes of Microsomal Vesicles from Maize Coleoptiles  
 Abstract    Vesicles prepared from the microsomal membrane fraction of maize coleoptiles possess an ATP-fueled H +-transport into the vesicles. It is highly possible that the vesicles from the microsomal membrane fraction actually are unchanged, native vesicles (originating from the ER or Golgi-apparatus) that can fuse with the plasmalemma or the vacuole. Therefore, they can reflect properties of the vacuole or the plasmalemma. The energy dependent acidification within the vesicles, which can be completely reverted through the addition o f CCCP, was determined on the basis o f photometric difference spectra using NR (Hager et al., Z. Naturforsch. 35 c, 7 9 4 -8 0 4 1980). The proton pumps possess a very high substrate specificity; only ATP (+ Mg2+) can be used as substrate, while GTP, ITP, UTP and CTP or other nucleoside tri-or diphosphates cannot be used. DCCD and DES inhibit H +-ATPase completely, oligomycin has only a slight, orthovanadate no inhibitory effect at all. The energy dependent transport o f H+ across the membrane takes place only in the presence of Cl-or Br-(not as well in the presence of I-). Other anions (F~, N O j, SOI-, SC N -, ID A -, H2BOj cannot cause an intravesicular acidification through ATP if chloride (or Br-) is not present. In the presence o f chloride, however, some of these anions inibit the H +/C l--symport (J-, N O j, SO2-, SCN-, H2BO j). They obviously are in competitive interaction with Cl-ions for Cl~-binding sites on a carrier or channel without being able to be transported themselves. Pi, which renders the acidification of the vesicles at a low rate possible without Cl-, is the only tested anion which can augment the Cl-dependent acidification. This supports the idea that either Pi functions as a positive effector on the Cl "-transport or that a Cl ~/Pi-anti porter exists which reduces Cl-accumulation and therefore facilitates the Cl-coupled H + transport into the vesicles also. The anion transport inhibitor, DIDS, blocks the ATP-dependent HMransport. This again supports the idea o f a relatively tight coupling between H + and Cl-transport in a possibly electroneutral system. The presence o f monovalent cations, such as K +, N a+, Li+ and choline*, are not important for H + transport. The dependence o f the ATP-fueled acidification of the vesicles on the same anion pattern which seems to regulate elongation growth and stomata aperture speaks for the eminent importance o f the H +-pump and vesicles described in this report for growth and turgor o f plant cells. 
  Reference    Z. Naturforsch. 36c, 997—1008 (1981); received September 2 1981 
  Published    1981 
  Keywords    Proton Pump, H +-ATPase, Cl--Channel, Coleoptile, Auxin 
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 TEI-XML for    default:Reihe_C/36/ZNC-1981-36c-0997.pdf 
 Identifier    ZNC-1981-36c-0997 
 Volume    36 
2Author    A. Hager, P. HermsdorfRequires cookie*
 Title    A H +/Ca2+ Antiporter in Membranes of Microsomal Vesicles from Maize Coleoptiles, a Secondary Energized Ca2+ Pump  
 Abstract    Microsomal vesicles prepared from the ER and the Golgi apparatus o f maize coleoptiles possess an ATP-fueled, Cl_-dependent proton pump which can cause an intravesicular acidifica­ tion of the vesicles (A. Hager. This acidification is very specifically inhibited by Ca2+. The inhibition is already distinct at concentrations o f 30 hm. While 10-fold higher concentrations of La3+ produce similar effects, Mg2+ remains ineffective even at very high concentrations. If Ca2+ is added after acidification o f the vesicles, a rapid H +-efflux proportional to the amount of Ca2+ added characterizes the first reaction phase. In the second reaction phase acidification within the vesicles commences anew, however, at a reduced rate. If Ca2+ is added to vesicles whose proton pump has been inhibited by DCCD, the first reaction phase remains unchanged, while the acidification in the second reaction phase does not set in, and only a leak out o f protons is observed. These results give support for a H +/C a2+-antiporter mechanism which can function as a secondary energized Ca2+-pump and regulate the Ca2+-concentration in the cytoplasm. 
  Reference    Z. Naturforsch. 36c, 1009—1012 (1981); received September 2 1981 
  Published    1981 
  Keywords    Ca2+ Pump, H+-ATPase, Membrane Vesicles, Coleoptile, Zea mays 
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 TEI-XML for    default:Reihe_C/36/ZNC-1981-36c-1009.pdf 
 Identifier    ZNC-1981-36c-1009 
 Volume    36