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.
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.
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D004285:Dogs; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
chemical_list: D006160:Guanosine Triphosphate; D009597:4-Nitrophenylphosphatase; D000252:Calcium-Transporting ATPases; D002118:Calcium