title: Occlusion of Rb+ after extensive tryptic digestion of shark rectal gland Na,K-ATPase.
abstract: Na,K-ATPase from rectal glands of Squalus acanthias has been subjected to proteolysis with trypsin. The E1- and E2-forms of the enzyme can be distinguished from the inactivation patterns at low trypsin concentrations, as previously seen with kidney enzyme. Extensive degradation by trypsin in the presence of 5 mM Rb+ yields membrane fragments with a 19 kDa peptide as the major proteolytic fragment of the alpha-subunit. The sequence of the N-terminal 40 residues of this peptide is almost identical to that of a similar proteolytic fragment isolated by Capasso et al. (Capasso, J.M., Hoving, S., Tal, D.M., Goldshleger, R. and Karlish, S.J.D. (1992) J. Biol. Chem. 267, 1150-1158) using kidney Na,K-ATPase. Rb+ occlusion can be fully retained under these circumstances, supporting the findings with kidney enzyme that only minor parts of the alpha-subunit are required to form a functional occlusion-site.
authors.affiliation: Institute of Biophysics, University of Aarhus, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Esmann
authors.forename: L
authors.initials: L
authors.lastname: Sottrup-Jensen
mesh_terms: D000595:Amino Acid Sequence; D001003:Anal Canal / Q000201:enzymology*; D000818:Animals; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000032:analysis; D012413:Rubidium / Q000378:metabolism*; D012754:Sharks; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000302:isolation & purification*; D014357:Trypsin
chemical_list: D010446:Peptide Fragments; D014357:Trypsin; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium