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|Type:||Artigo de periódico|
|Title:||2 K-M'S FOR ATP OF CORN-ROOT H+-ATPASE AND THE USE OF GLUCOSE-6-PHOSPHATE AND HEXOKINASE AS AN ATP-REGENERATING SYSTEM|
|Abstract:||Plasma membrane vesicles derived from corn (Zea mays L.) roots retain a membrane-bound H+-ATPase that is able to form a H+ gradient across the vesicle membranes. The activity of this ATPase is enhanced 2- to 3-fold when Triton X-100 or lysophosphatidylcholine is added to the medium at a protein:detergent ratio of 2:1 (w/w). In the absence of detergent, the ATPase exhibits only one K-m for ATP (0.1-0.2 mM), which is the same as for the pumping of H+. After the addition of either Triton X-100 or lysophosphatidylcholine, two K-m's for ATP are detected, one in the range of 1 to 3 mu M and a second in the range of 0.1 to 0.2 mM. The V-max of the second K-m, for ATP increases as the temperature of the assay medium is raised from 15 degrees C to 38 degrees C. The Arrhenius plot reveals a single break at 30 degrees C, both in the absence and in the presence of detergents. In the presence of Triton X-100 the H+-ATPase catalyzes the cleavage of glucose-6-phosphate when both hexokinase and ADP are included in the assay medium. There is no measurable cleavage when the apparent affinity for ATP of the H+-ATPase is not enhanced by Triton X-100 or when 1 mM glucose is included in the assay medium. These data indicate that when the high-affinity K-m for ATP is unmasked with the use of detergent, the ATPase can use glucose-6-phosphate and hexokinase as an ATP-regenerating system.|
|Editor:||Amer Soc Plant Physiologists|
|Appears in Collections:||Artigos e Materiais de Revistas Científicas - Unicamp|
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