Abstract
The pCa (-log [Ca]) dependence of myofibrillar MgATPase, mitochondrial Ca2+ uptake, state 3 and state 4 respiration rates were measured under identical conditions in the presence of 2.5 m~ M&+. The pCa of each solution was maintained with 10 m~ EGTA in both sucrose and KC1-containing media. Myofibrillar MgATPase varied from 10-90% of maximal activation between pCa 6.2 and 5.4 in the sucrose medium and between pCa 6.5 and 5.5 in the KC1 medium. Within
Highlights
+ From the Section of Contractile Proteins, §Department of Pharmacology and Cell Biophysics, University of Cincinnati
The pCa of each solution was maintained with 10 m~ EGTA in both sucrose and KC1-containing media
Myofibrillar MgATPase varied from 10-90% of maximal activation between pCa 6.2 and 5.4 in the sucrose medium and between pCa 6.5 and 5.5 in the KC1 medium
Summary
The assay media for both oxygen consumption and Ca2+uptake measurements contained either 240 mM sucrose or 150 mMKC1, 10 mM EGTA-Tris, 10 mM HEPES, k2.5 mMMgC12, and various amounts ofCaC12 at pH 7.0. Mg2+ depressed the uptake following removal of the mitochondria by centrifugation at 15,000 X g.Making this supernatant 6% in trichloracetic acid and 1%in LaCl:$ produced a precipitate whichwas removed by centrifugation before measuring the metal concentrations in the final supernatant. By this method, we found the Mg2+and Ca2+ contentosf our isolated mitochondria to be 12.16 f 1.74 nmol/mg and 1.04 f 0.35 nmol/mg, respectively. Protein was determined by the method of Lowry et al (19)
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