Studies on Cathepsins of Rat Liver Lysosomes

I. Purification and Multiple Forms

Abstract

Cathepsins A, B, C, and D were purified from the lysosome fraction of rat liver by ammonium sulfate fractionation, followed by Sephadex G-200 and DEAE-Sephadex chromatography, and evidence was presented for multiple forms of each cathepsin.
By gel filtration, each of cathepsin A, B, and D was separated into several fractions. Molecular weights estimated by the chromatography were 100, 000, 180, 000, 400, 000 for A_I, A_II, A_III, and 24, 000, 50, 000 for B_I, B_II, respectively, 150, 000 for C, and 24, 000 for the main peak of D (D_I).
On DEAE-Sephadex chromatography, several peakes of cathepsin C, named C_I, C_II, C_III, appeared. The chromatographic pattern changed considerably in the presence of dithioerythritol, and cathepsin C became separable from cathepsin A.
By the above procedures, cathepsin A was purified 800- to 3, 000-fold, and cathepsin B, C, and D were purified 2, 100-, 480-, and 200-fold, respectively, over liver homogenate.
Cathepsin A multiple forms (isoenzymes), A_I, A_II, A_III appeared to have immunologically identical moieties in common, on the basis of immunodiffusion analysis. Their molecular weights suggest that they are monomer, dimer, and tetramer.
Cathepsin C_I, C_II, and G_III showed the same precipitin line in immunodiffusion analysis, and appear to be immunologically closely related, if not identical.