Effect of methanol on spinach thylakoid ATPase

Methanol at 35% ($\text{v}\text{v}$) overcomes the latency of spinach thylakoid ATPase. Activation is immediate and reversible involving changes in the V_max, not the K_m of the enzyme, MgATP is a much better substrate than CaATP; free Mg²⁺ noncompetitively inhibits activity. This inhibition can be overcome by the addition of Na₂SO₃. While both MgATP and MgGTP act as substrates, free ATP and GTP both inhibit activity. ADP and MgADP are also inhibitory. Insensitivity to certain inhibitors indicates that methanol neither induces the same conformational changes in CF₁ as illumination does, nor does it lead to coupling between H⁺ movement through CF₀ and ATP hydrolysis. Methanol activation provides a much improved method for assaying thylakoid ATPase.