Identification of the pH-dependent membrane anchor of carboxypeptidase E (EC 3.4.17.10)

• Published in: The Journal of biological chemistry 1990-02, Vol.265 (5), p.2476-2482
• Main Authors: Fricker, L D, Das, B, Angeletti, R H
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Analytical, structural and metabolic biochemistry; Animals; Binding Sites; Biological and medical sciences; Carboxypeptidase H; Carboxypeptidases - genetics; Carboxypeptidases - metabolism; Cattle; Cell Membrane - enzymology; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; Hydrogen-Ion Concentration; Hydrolases; Kinetics; Molecular Sequence Data; Peptides - chemical synthesis; Peptides - metabolism; Pituitary Gland - enzymology; Protein Binding; Protein Conformation; Rats
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(19)39824-2

Carboxypeptidase E (CPE), a peptide hormone-processing enzyme, is present within secretory granules in both a soluble form and a form which is membrane-bound at pH 5.5 but soluble at neutral pH. Antisera raised against a peptide corresponding to the predicted COOH-terminus of CPE bind to the membrane-associated form of CPE but not to the soluble form. This COOH-terminal region is predicted to form an amphiphilic alpha-helix, containing several pairs of hydrophobic residues separated by hydrophilic residues. Synthetic COOH-terminal peptides 11-24 residues in length are able to bind to bovine pituitary membranes and can be extracted by conditions that extract the membrane-bound form of CPE. The influence of pH on the membrane binding of a 21-residue COOH-terminal peptide is similar to the membrane binding of CPE: at pH values less than 6 the majority of the peptide is membrane-bound, while at pH values above 8 less than 20% is membrane-bound. Both the 21-residue COOH-terminal peptide and the purified membrane form of CPE, but not the soluble form, partition into Triton X-114 only at low pH (pH less than 6). Combined polar and hydrophobic interactions of the COOH-terminal peptide appear to be responsible for the reversible, pH-dependent association of CPE with membranes.