Open AccessMeasurement of Mitochondrial ATPase Activity in Maize Root Tips by Saturation Transfer 31P Nuclear Magnetic Resonance
Author(s) -
Justin K. M. Roberts,
David E. Wemmer,
Oleg Jardetzky
Publication year - 1984
Publication title -
plant physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.554
H-Index - 312
eISSN - 1532-2548
pISSN - 0032-0889
DOI - 10.1104/pp.74.3.632
Subject(s) - atp synthase , mitochondrion , cytoplasm , atpase , saturation (graph theory) , biophysics , biochemistry , chemistry , biology , enzyme , mathematics , combinatorics
We show that saturation transfer (31)P nuclear magnetic resonance can be used to measure the activity of the mitochondrial ATPase of maize (Zea mays L. hybrid WW x Br38) root tips in vivo. Unidirectional rates of ATP synthesis were determined in the steady state (i.e. ATP and cytoplasmic orthophosphate constant) under various conditions. These measurements, and determinations of oxygen consumption, give a P/O ratio (measured in the living tissue) close to 3. In succinate-fed root tips the P/O ratio is approximately 2. Cyanide inhibits the rate of ATP synthesis by two-thirds (P/O ratio approximately 1), with an effective inhibitor constant of approximately 35 micromolars. We show that the alternative electron pathway cannot make ATP, and does not normally operate in this tissue. This method of studying plant mitochondrial metabolism avoids potential artifacts encountered in studies using isolated and purified mitochondria. The method also allows, for the first time, direct and simultaneous examination of the relationship between the rate of ATP synthesis and levels of metabolites such as ATP, and derived parameters such as phosphorylation potential.