Cation-stimulated ATPase activity in purified plasma membranes from tobacco hornworm midgut.

摘要: Abstract Purified goblet cell apical membranes from Manduca sexta larval midgut exhibit a specific ATPase activity approx. 20-fold higher than that in the 100 000 × g pellet of homogenate. The already substantial this plasma membrane segment is doubled presence 20–50 mM KCl. At ATP concentrations ranging 0.1 to 3.0 mM, 20 KCl leads 10-fold increase enzyme's affinity for ATP. greatest at pH 8. In addition ATP, GTP serves as substrate, but CTP, ADP, AMP and p-nitrophenyl phosphate do not. Either Mg2+ or Mn2+ required cannot be replaced by Ca2+ Zn2+. inhibited neither typical (Na+ + K+)-ATPase inhibitors, ouabain orthovanadate, nor mitochondrial F1F0-ATPase azide oligomycin. Although 1.5 μM DCCD ineffective, 150 total inhibition activity. stimulated not only K+, also, order decreasing effectiveness, Rb+, Li+, Na+ even Mg2+. Replacement Cl− Br−, F− HCO3− has less influence variation cations. However, replacement NO3− inhibits strongly described above characteristic alkali metal ion pump containing cells enhanced similar degree other purified epithelial segments. Its localization, its broad cation specificity insensitivity all mimic properties active transport lepidopteran suggest possible key component electrogenic pump.