Reversal of copper inhibition in chloroplast reactions by manganese.

In the Mehler reaction, a Hill reaction utilizing molecular oxygen as the electron acceptor, rates of net oxygen uptake are stimulated by added manganous ions. Both whole cell photosynthesis and the Mehler reaction are inhibited by copper. Copper inhibition of the Mehler reaction can be reversed by manganese salts. Glutathione. which alone has no effect on Mehler reaction rates, enhances the effect of manganese in reversing copper inhibition. The effects of added Cu(2+), Cu(2+) and Mn(2+), or Cu(2+), Mn(2+), and glutathione exhibit no induction phenomena when measured manometrically. Furthermore, the order of addition of these factors is unimportant: final rates are dependent only on the composition of reaction mixtures. Compared to the Mehler reaction, conventional Hill reactions are less sensitive to copper poisoning, while certain chloroplast mediated photoxidations (e.g. the photoxidation of diketogulonic acid) are far more sensitive. In all of the chloroplast mediated photoreactions tested, manganese is effective in reducing the sensitivity to copper poisoning.