Properties of cathepsin C from rat liver

Abstract

1. 1. Rat liver cathepsin C (EC 3.4.4.9) was purified 1790-fold over the homogenate activity by a purification scheme that combined the techniques of centrifugation, acid precipitation, (NH 4) 2SO 4 precipitation, and Sephadex G-200, DEAE-cellulose, and CM-cellulose column fractionations. 2. 2. The specific activity of the most purified CM-fraction with Gly-Tyr-NH 2 as substrate was 91.6 μmoles of hydroxamate produced per mg of protein per min, which is higher than previously reported values. 3. 3. The K m for Gly-Tyr-NH 2 was 6 mM when determined by hydroxamate formation, and that for Val-Leu-NH 2 was 2.5 mM. 4. 4. The requirements for −SH compounds and for halide ions for activity were absolute. A dithioerythritol concentration of 25 mM and a Cl − or Br − concentration of 10 mM were required for full activation. 5. 5. The enzyme catalyzed a hydrolysis reaction at pH 5, but the polymerization reaction catalyzed at pH 7–8 occurred at a greater rate. 6. 6. The substrate specificity of cathepsin C was broader than that reported in older literature and the enzyme was confirmed to be a dipeptidyl aminopeptidase that acts upon a number of dipeptide amides and tripeptides. The most favorable substrates were tripeptides or dipeptide amides that have as the NH 2-terminal group a small residue and that have the aliphatic residue leucine at the penultimate position.