Characterisation of the Enzyme Intermediates of the Sarcoplasmic Transport ATPase by the Use of Inhibitors

Abstract

Sarcoplasmic Transport ATPase, Enzymes Intermediates 1. Based on a detailed reaction scheme of the phosphorylation process of the sarcoplasmic transport ATPase the inhibition mechanisms o f benzoctamine, DIO 9, AMP-PNP and of Ca2+-ions at relatively high concentrations (1 ~ 100 |iM) were determined.2. The inhibition mechanisms were analyzed by measuring the y-phosphate exchange between ATP and ADP and evaluated by applying conventional and an extended Dixon plot procedures.3. The kinetic patterns o f the inhibition were shown to be com patible with the assumed reaction scheme.4. Each inhibitor combines with definite interm ediates: Benzoctamine with the interm ediate species m *"2E and £fg22E-ATP; AM P-PNP with ~ P; DIO 9 with E and MgE and Ca2+ at rela tively hign concentrations with E.5. The central interm ediate blocked by benzoctamine can partially exist as Mg2 2E pDP-benzoctamine which is detected as phosphoprotein after acid denaturation.