Electron transport coupled to quasi-arsenylation in isolated chloroplasts

Ferricyanide reduction in isolated chloroplasts has been known to be inhibited by ATP. AMP and arsenate restored this ATP-inhibited ferricyanide-reducing acitivity. The nature of restoration caused by an ATP-AMP-arsenate system (termed here quasi-arsenylation) was found to be quite similar to the nature of restoration coupled to phosphorylation or arsenylation. The optimum pH for both arsenylation and quasi-arsenylation was around 8.3. From a preliminary analysis of the restoration process by quasi-arsenylation, the apparentKm values for ATP (at AMP=∞) and AMP (at ATP=∞) were estimated to be around 20 and 6 μM, respectively. The mechanism of restoration coupled to quasi-arsenylation is discussed in relation to the chloroplast coupling factor (CF₁) which can bind either two ADP molecules or one each of ATP and AMP molecules.