Document Detail

Measurement of the electrochemical proton gradient in submitochondrial particles.
MedLine Citation:
PMID:  6296098     Owner:  NLM     Status:  MEDLINE    
The pH gradient and membrane potential of submitochondrial particles from bovine heart were estimated by the uptake of [14C]ethylamine and [36Cl]perchlorate, using filtration through a glass fiber prefilter and Millipore filter without washing to separate the vesicles from the medium. An external volume probe of [3H] sucrose was also used. Internal volume of the vesicles was measured by the extent of uptake of glucose, which equilibrates slowly across the membrane. The electrochemical potential gradient of H+ (delta micro H+) calculated from uptake of ethylamine and perchlorate, assuming the ions taken up were free in solution inside the vesicles, was 23 to 24 kJ/mol of H+ (240-250 mV) during respiration in the absence of ATP. The ratio of the free energy of ATP synthesis (delta GATP) to delta micro H+ was 2.2 to 2.3 during oxidative phosphorylation and only slightly higher during ATP hydrolysis indicating that the H+-translocating ATPase is close to equilibrium under both conditions. The nonintegral ratio suggests there is a systematic error in the measurement of delta micro H+. The value of delta micro H+ calculated from ion uptake could be too high if some of the ions taken up are bound to the membrane or concentrated into the electric double layer at the inner membrane-water interface. The effects of vesicle volume (varied osmotically) and permeant ions (which affect internal ionic strength and pH) on the ratio of delta GATP to delta micro H+ suggested that ion association with the membrane in fact caused significant overestimation of delta micro H+. Association of ethylammonium and perchlorate ions with unenergized submitochondrial particles was measured by centrifugation, in the presence of a high concentration of impermeant salt to minimize association with the external surface. The results were used to estimate the extent of binding during the ion uptake assays, and delta micro H+ was recalculated taking this binding into account. The resulting values were between 19 and 20 kJ/mol of H+ (197-207 mV) during respiration in the absence of ADP, and the ratio of delta GATP to delta micro H+ was about 3 during oxidative phosphorylation.
E A Berry; P C Hinkle
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  The Journal of biological chemistry     Volume:  258     ISSN:  0021-9258     ISO Abbreviation:  J. Biol. Chem.     Publication Date:  1983 Feb 
Date Detail:
Created Date:  1983-03-17     Completed Date:  1983-03-17     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  2985121R     Medline TA:  J Biol Chem     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  1474-86     Citation Subset:  IM    
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MeSH Terms
Ammonia / metabolism
Biological Transport
Ethylamines / metabolism
Hydrogen-Ion Concentration
Membrane Potentials
Mitochondria / physiology*
Mitochondria, Heart / physiology*
Perchloric Acid / metabolism
Submitochondrial Particles / physiology*
Sugar Acids / pharmacology
Thiocyanates / metabolism
Grant Support
Reg. No./Substance:
0/Ethylamines; 0/Sugar Acids; 0/Thiocyanates; 7601-90-3/Perchloric Acid; 7664-41-7/Ammonia

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