title: The effect of temperature on the acetylcholinesterase activity of muscle microsomes.
abstract: Membrane vesicles which constitute the sarcotubular system were separated and the fraction enriched in T-tubules purified by a calcium loading procedure. The preparations of unfractioned microsomes and T-tubules have been analyzed for their relative content of enzyme markers and acetylcholinesterase. The amount of this enzyme in the T-tubule fraction was higher than in mixed microsomes but less than two-fold the value of vesicles derived from sarcoplasmic reticulum. Arrhenius plots of membrane-bound and soluble acetylcholinesterase from either mixed microsomes or fractions enriched in T-tubules show an anomalous behaviour as two break points were obtained. The first discontinuity was found at about 17 degrees C for membrane-bound, and 12-14 degrees C for soluble acetylcholinesterase. The second one being at about 25 degrees C for both particulate and detergent-solubilized enzyme. The changes in activity with temperature suggest that lipid-protein, detergent-protein and protein-protein interactions might be involved in the stabilization of the enzyme both in the natural membrane and in the soluble state.
mesh_terms: D000110:Acetylcholinesterase / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008861:Microsomes / Q000201:enzymology*; D009132:Muscles / Q000201:enzymology*; D011817:Rabbits; D013696:Temperature; D013816:Thermodynamics
chemical_list: D000110:Acetylcholinesterase; D017301:Ca(2+) Mg(2+)-ATPase