Glycerol titration distinguished from free water the local hydration shell involved in ATPase transition from active to inactive, with cooperativity for water n=16. Rat brain cortex: NE-stimulated and its basal adenylyl cyclase (AC) in the absence of free Mg~(2+), allows a refractive state of AC with negative cooperativity for MgATP and ATP~(4+). This allows an AC refractory period which allows integrative control by the supply of ionic Mg~(2+). Mg~(2+) with cooperativity n=3.7 activates NE-AC. The erythrocyte-Hb system operates as a metabolic sensor to match glucose availability with the release of Hb-carried, O2 and Mg~(2+) at CSF. [Mg(H2O)_6](H_2O)_(12)~(2+) by chelating either a protein or ATP~(4+) losses most of its hydration shell. The ion pump ATPase by forming ADP3" releases an incompletely hydrated Mg~(2+), which could capture H_2O from either [Na.(H_2O)_6]~+ or [K.(H_2O)_6]~+. Thus, sieve-sizing their hydration shells for fitting into Na~+-pump channels.Keywords: hydrated ATPase, refractory adenylate cyclase, hydration shells sizing, Mg~(2+)-coupling, Hb-O_2/Mg~(2+)-carrier, LTM retrieval
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