title: The influence of pH on the degradation of bovine myelin basic protein by bovine brain cathepsin.
abstract: The degradation of bovine myelin basic protein by bovine brain cathepsin D (ED 3.4.23.5) was studied over a pH range of 2.75 - 6.0. Throughout this pH range pepstatin, an inhibitor of cathepsin D, prevented the degradation. The degradation at a pH away from the optimum of pH 3.5 was predictably slower, but also resulted in more restricted cleavage. Above pH 4.5 bovine basic protein peptide 1 - 42 was not degraded further to peptide 1 - 36 as occurs at pH 3.5. Additionally, at pH 5.5 another fragment of basic protein, peptide 1 - 91, persisted indicating that under certain basic protein as well as basic protein peptide 43 - 169 may be cleaved in the molecular region of basic protein around the phenylalanyl-phenylalanine residues at position 88 - 89. The small amount of peptides 1 - 91 and 92 - 169 detected at pH 5.5 suggests that the bond between residues 91 and 92 in intact basic protein is a minor cleavage site. The options and variation in cleavage around residues 88 - 92 of basic protein presumably result from pH-dependent changes in conformation in the is region but could also be due to changes in conformation of cathepsin D. These results indicate that local tissue changes such a pH amy affect not only the velocity of the reaction but also the nature of th product formed by the degradation of basic protein by brain cathepsin D
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002402:Cathepsin D; D002403:Cathepsins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D004676:Myelin Basic Protein / Q000378:metabolism*; D010436:Pepstatins / Q000494:pharmacology; D010446:Peptide Fragments / Q000378:metabolism; D011487:Protein Conformation
chemical_list: D000596:Amino Acids; D004676:Myelin Basic Protein; D010436:Pepstatins; D010446:Peptide Fragments; D002403:Cathepsins; D002402:Cathepsin D