Showing papers by "Sabeeha S. Merchant published in 1985"
TL;DR: Photosynthetic coupling factor ATPases generally censist of five subunits named α, β, γ, δ and ε in order of decreasing apparent molecular weight, which are the most strongly related, although the α and γ subunits also show significant immunological cross-reactivity.
Abstract: Photosynthetic coupling factor ATPases (F1-ATPases) generally censist of five subunits named α, β, γ, δ and e in order of decreasing apparent molecular weight. The isolated enzyme has a molecular weight of between 390,000 to 400,000, with the five subunits probably occurring in a 3:3:1:1:1 ratio. Some photosynthetic F1 ATPases are inactive as isolated and require treatment with protease, heat or detergent in order to elicit ATPase activity. This activity is sensitive to inhibition by free divalent cations and appears to be more specific for Ca2+ vs. Mg2+ as the metal ion substrate chelate. This preference for Ca2+ can be explained by the higher inhibition constant for inhibition of ATPase activity by free Ca2+. Methods for the assay of a Mg-dependent ATPase activity have recently been described. These depend on the presence of organic solvents or detergents in the reaction mixture for assay. The molecular mechanism behind the expression of either the Ca- or Mg-ATPase activities is unknown. F1-ATPases function to couple proton efflux from thylakoid membranes or chromatophores to ATP synthesis. The isolated enzyme may thus also be assayed for the reconstitution of ‘coupling activity’ to membranes depleted of coupling factor 1.
32 citations