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  • Title: Roussel award for cardiology. The mechanism of nucleotide induced calcium translocation across sarcoplasmic reticulum membranes: evidence for a non-translocated intermediate pool of calcium.
    Author: Entman ML, Bick R, Chu A, Van Winkle WB, Tate CA.
    Journal: J Mol Cell Cardiol; 1986 Aug; 18(8):781-91. PubMed ID: 3018265.
    Abstract:
    Our previous data suggested that, in cardiac muscle sarcoplasmic reticulum fragments, GTP hydrolysis occurs by an alternative enzyme cycle of the Ca2+ ATPase which is insensitive to (Ca2+) and does not involve an acyl phosphate intermediate. Despite this, GTP induces the incorporation of calcium into a membrane pool that is not translocated to the vesicular lumen. The present study suggests that this GTP-induced intermediate calcium pool is identical to a modulable component of the calcium translocation process in that: it has an identical pH sensitivity; the initial incorporation of calcium in response to GTP eliminates the initial rapid burst and lag component of the typical ATP-induced calcium uptake curve when ATP is added during GTP-induced calcium accumulation. Instead, the addition of ATP during GTP-induced calcium accumulation results in the prompt onset of the linear phase of calcium translocation; GTP-induced calcium accumulation directly affects the pH sensitivity of subsequent ATP-induced calcium accumulation. We suggest that the intermediate calcium pool is in series with calcium translocation and is the site of the pH sensitivity observed in calcium flux.
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