Quantitative relationship between the protein secondary structure in cardiac sarcolemma and the activity of the...

In the absence of ATP, increasing concentrations of calcium within a range between 0.1--8.0 mmol . 1(-1) gradually lowered the alpha-helix content of proteins in rat heart sarcolemma requiring no energy supply. In the presence of ATP, similar concentrations of calcium stepwise activated the sarcolemmal low-affinity Ca2+-ATPase. A mathematical analysis of the data obtained revealed a quantitative relationship between calcium-induced stimulation of the Ca2+-ATPase activity and a diminution of the alpha-helix contents of membrane proteins in cardiac sarcolemma. The cooperation between changes in protein conformation and energy consumption in relation to the supposed role of low-affinity Ca2+-ATPase in gating the calcium channel are discussed.