The two Km's for ATP of corn-root H+-ATPase and the use of glucose-6-phosphate and hexokinase as an ATP-regenerating system

• Published in: Plant physiology (Bethesda) Vol. 105; no. 3; pp. 853 - 859
• Main Authors: RAMOS, R. S, CALDEIRA, M. T, ARRUDA, P, DE MEIS, L
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01-07-1994
• Subjects: actividad enzimatica; activite enzymatique; adenosina trifosfatasa; adenosine triphosphatase; Adenosine triphosphatases; adenosine triphosphate; adenosintrifosfato; Agronomy. Soil science and plant productions; azucares fosfatos; Bioenergetics; Biological and medical sciences; Cell membranes; Cell physiology; cell structure; Corn; culture media; Detergents; Enzymes; enzymic activity; estructura celular; Fundamental and applied biological sciences. Psychology; hexokinase; hexoquinasa; Hydrolysis; medio de cultivo; milieu de culture; Plant physiology and development; Plant roots; Plants; Plasma membrane and permeation; racine; raices; roots; Sodium; structure cellulaire; sucre phosphate; sugar phosphates; Vanadates; zea mays; Monocotyledones; Temperature; Detergent; Zea mays; Enzyme; Triton; H; Proton gradient; Cereal crop; Lysophosphatidylcholine; transporting ATPase; Enzymatic activity; Gramineae; Michaelis constant; Angiospermae; Plasma membrane; Hydrolases; Spermatophyta; ATP
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.105.3.853

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 Km 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 Km's for ATP are detected, one in the range of 1 to 3 micromolar and a second in the range of 0.1 to 0.2 mM. The Vmax of the second Km 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 Km for ATP is unmasked with the use of detergent, the ATPase can use glucose-6-phosphate and hexokinase as an ATP-regenerating system.