The Accumulation and the Release of Divalent Cations Across Mitochondrial Membranes

Abstract

Accumulated divalent cations and phosphate (P.) in isolated bean mitochondria are released by conditions which inhibit respiration, including anaerobiosis and KCN, or by conditions which divert conserved energy from divalent cation uptake. These include ATP synthesis, KT transport in the presence of valinomycin, and the presence of the uncouplers, 2,4-dinitrophenol and oleic acid. The results indicate that plant mitochondria are not permanent deposit sites for divalent cation and PI salts but, rather, function as temporary sequestering sites for these ions.It is suggested that mitochondria may play a role in the control of the movement as well as a regulation of the concentrations of these ions within the cell.

Calcium Deposition in the Myxomycete Didymium squamulosum

“…The presence of phosporus in the peridial deposits of some physaraceous species (Schoknecht, unpublished) suggests that retention or deposition of the phosphorus component of the granules may be a specific characteristic. In bone and vascular plants the release of mitochondrial calcium and phosphorus is apparently related to respiration and availability of conserved mitochondrial energy (Carafoli, 1967;Lehninger, 1970;Matthews et al, 1970;and Johnson and Wilson, 1973). However, no physiological data are presently available which would indicate that a similar energy-dependent mechanism is operative in the Myxomycetes.…”

Respiration-independent Binding of SR2+ to Bean Mitochondria

“…While a biphasic curve for Sr' binding is observed, the binding sites do not correspond to the high and low affinity binding sites reported for rat liver and other vertebrate mitochondria (13). The higher affinity binding site in Figure 1 has a dissociation constant of 25 x 0I and binds In bean mitochondria DNP3 inhibits Sr2+ transport approximately 85 to 90%, as well as promoting the discharge of previously accumulated Sr2` (7,8). However, DNP diminishes only partially the Sr2`binding at all concentrations (Fig.…”

“…Support for this possibility comes from the similarity in the dissociation constant for Sr2+ binding which is 25 btM and the Kin for Sr2+ transport which is 30 ftM under similar conditions (6). Further, the partial inhibition of both Sr2+ binding and transport by DNP and valinomycin plus K+ may reflect a similarity in both binding and transport sites, although with these compounds as well as with ruthenium red the inhibition of active transport was greater than the inhibition of binding (6) The lack of high affinity divalent cation binding sites in bean mitochondria equivalent to that observed in mitochondria from vertebrates may account for the low priority that the divalent cation and Pi transport system assumes among the energy-utilizing events of electron transport in bean mitochondria, as well as the lack of a divalent cation stimulation of respiration (7,8). These results contrast with those for rat liver mitochondria where Ca2+-induced respiration is greater than the ADP-induced stimulation of respiration and thus assumes a higher priority in the hierarchy of energy-utilizing processes in mitochondria (2).…”

The Effects of Ten Phenolic Compounds on Hypocotyl Growth and Mitochondrial Metabolism of Mung Bean

“…Calcium uptake was followed as previously described (Johnson and Wilson, 1972) except that the mitochondria were harvested after 8 min incubation by centrifugation through 5 ml of 0.8 M mannitol at 31,000 g for 5 min at room temperature. The Ca 2 + level was measured on an atomic absorption spectrophotometer.…”