The inactivation by concanavalin A of the ecto-ATPase and ectoacetylcholinesterase of intact skeletal muscles.
The (Ca2+ or Mg2+)-activated ectophosphohydrolase of intact frog muscle liberates, in situ, about 37 mumol inorganic phosphate/g muscle in 20 min at 20 degrees C with 10 mM ATP. Pretreatment with concanavalin A (ConA) at 4 degrees C for 18 h caused ectoenzyme inactivation which plateaued at 35-40% of the control rate. The inhibition was concentration dependent, being maximal at about 500 micrograms ConA/mL Ringer's solution. The lectin mediated its effect via the membrane glycoproteins since the inhibition was specifically prevented by alpha-methyl D-mannopyranoside. As the temperature increased from 10 to 40 degrees C, the ectoenzyme activity of untreated muscles increased linearly between 10 and 35 degrees C, with a "break point" and a clear change in slope at 35 degrees C. When treated with ConA the activity increased linearly from 10 to 40 degrees C, eliminating the transition temperature. The findings suggested that a phase transition toward fluidity in the lipid bilayer may have occurred at 35 degrees C and that this was abolished by the lectin binding. Hence we perturbed the surface membrane phospholipids of muscle pretreated with the lectin. Phospholipase C increased the activation by the lectin; phospholipase D had no effect, but phospholipase A2 completely prevented it. The lectin may require the more fluid fatty acyl chains of membrane lipids to achieve inhibition of this ecto-ATPase. Ectoacetylcholinesterase, in situ, and its inactivation by ConA were measured directly on whole, intact skeletal muscles.
D000110:Acetylcholinesterase / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors*; D000818:Animals; D003208:Concanavalin A / Q000494:pharmacology*; D006023:Glycoproteins / Q000378:metabolism; D008362:Mannosides / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism; D009132:Muscles / Q000201:enzymology*; D010740:Phospholipases / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D011894:Rana pipiens; D013696:Temperature
D006023:Glycoproteins; D008362:Mannosides; D008565:Membrane Proteins; D010743:Phospholipids; D003208:Concanavalin A; D010740:Phospholipases; D000110:Acetylcholinesterase; D000251:Adenosine Triphosphatases