title: Synthesis and hydrolysis by pepsin and trypsin of a cyclic hexapeptide containing lysine and phenylalanine.
abstract: 1. A cyclic hexapeptide, cyclo(-Gly2-Phe2-Gly-Lys-), and the corresponding open-chain hexapeptides, Gly2-Phe2-Gly-Lys and Phe-Gly-Lys-Gly2-Phe, have been synthesized and their susceptibilities to the hydrolytic action of pepsin and trypsin were determined. 2. The cyclic peptide was hydrolyzed slowly by trypsin to a hexapeptide Gly2-Phe2-Gly-Lys, the value of the Michaelis constant for this reaction being Km equals 0.00022 M. 3. The cyclic peptide was not cleaved by pepsin at all, but Gly2-Phe2-Gly-Lys was hydrolyzed rapidly at a Phe-Phe bond; Km equals 0.0091 M. 4. The cyclic peptide inhibits the hydrolysis of Gly2-Phe2-Gly-Lys by pepsin in a linear non-competitive manner, the value of the inhibition constant being Ki equals 0.004 M.
mesh_terms: D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008239:Lysine; D009842:Oligopeptides / Q000096:biosynthesis*; D010434:Pepsin A / Q000378:metabolism; D010456:Peptides, Cyclic / Q000096:biosynthesis*; D010649:Phenylalanine; D014357:Trypsin / Q000378:metabolism
chemical_list: D009842:Oligopeptides; D010456:Peptides, Cyclic; D010649:Phenylalanine; D014357:Trypsin; D010434:Pepsin A; D008239:Lysine