title: Tryptic digestion of the (Na + K)-ATPase is both sensitive to and modifies K+ interactions with the enzyme.
abstract: Tryptic digestion of the (Na + K)-ATPase in the presence of choline chloride or NaCl ("Na-type") and in the presence of KCl ("K-type") produced distinct patterns of peptide fragments and losses of catalytic activity. The K0.5 for K+ to shift digestion from the Na-type, and its sensitivity to dimethyl sulfoxide and Triton X-100, were consistent with K+ acting at sites on the cytoplasmic face of the enzyme through which the K-phosphatase reaction also is activated. Reagents favoring the E1 conformational states, oligomycin, Triton, and ATP, shifted the pattern toward the Na-type, whereas those favoring E2 states, dimethyl sulfoxide, MgCl2, and MnCl2, shifted the pattern toward the K-type. Na-type digestion caused a greater loss of K-phosphatase than (Na + K)-ATPase activity, and the residual K-phosphatase activity was more sensitive to inhibition by Triton and ATP but stimulated more by dimethyl sulfoxide and inhibited less by Pi and MnCl2; all these effects are consistent with such digestion shifting equilibria toward E1 enzyme states. Accordingly, the K0.5 for K+ to activate the (Na + K)-ATPase was increased. However, the K0.5 for the K-phosphatase was unchanged; this observation requires revision of previous formulations, and bears on additional aspects of enzyme activity as well.
mesh_terms: D000818:Animals; D002417:Cattle; D004789:Enzyme Activation / Q000187:drug effects; D006868:Hydrolysis; D066298:In Vitro Techniques; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D011188:Potassium / Q000378:metabolism*; D011487:Protein Conformation; D012964:Sodium / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014357:Trypsin / Q000494:pharmacology*
chemical_list: D012964:Sodium; D014357:Trypsin; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium