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Plant Physiology 64:281-284 (1979)
© 1979 American Society of Plant Biologists

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Articles

Energy-linked Adenosine Diphosphate Accumulation by Corn Mitochondria

II. Phosphate and Divalent Cation Requirement 1

Samir Abou-Khalil and John B. Hanson

a Department of Botany, University of Illinois, Urbana, Illinois 61801

The requirement for phosphate and Mg2+ in energy-linked [3H] ADP accumulation by corn mitochondria has been studied. Arsenate will fully substitute for phosphate; sulfate partially substitutes; acetate, bicarbonate, and pyrophosphate are ineffective. Phosphate is also taken up by the mitochondria, but the ADP/Pi ratio varies widely with experimental treatments. ADP does not exchange with endogenous labeled phosphate, although Pi/32Pi exchange occurs.

Mg2+ is also accumulated during ADP uptake. Mg2+ can be substituted with varying efficiency by other divalent cations, but not monovalent cations. Effective cations typically increase phosphate uptake, particularly Ca2+ · Ca2+ -activated ADP accumulation is insensitive to carboxyatractyloside over a wide range of Ca2+ concentrations. When Ca2+ is substituted for Mg2+ it is not necessary to block ATP formation to secure high levels of ADP accumulation, since Ca2+ will divert energy from ATP formation into ion uptake.

It is suggested that the transport mechanism may carry out a concerted transport of ADP and phosphate with bound divalent cation. The phosphate transporter may be involved, or alternatively a special mechanism for trivalent anion transport may exist which acts cooperatively with the phosphate transporter.

1 This research was supported by the Department of Energy Grant EY 76-S-02-0790.






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