Possible involvement of cathepsin L in processing of rat liver hexokinase to eliminate mitochondria-binding ability

A previously found proteinase possibly involved in the modification of hexokinase to eliminate the mitochondria-binding ability without appreciable change in the catalytic activity (called hexokinase-processing enzyme hereafter), was purified by sequential chromatographies from rat liver and its properties were examined. The hexokinase-processing enzyme had carbohydrate moieties as evidenced by adsorption on immobilized concanavalin A, and had a molecular weight of about 23,000 as estimated by SDS-PAGE and gel filtration chromatography. Benzyloxycarbonyl-phenylalanyl-L-arginlne-4-methylcou- maryl-7-amlde (Z-Phe-Arg-MCA)-hydrolyzing activity was co-purified with this processing activity throughout the purification, while the hydrolyzing activity for benzyloxycar bonyl-L-arglnyl-L-arglnine-4-methylcoumaryl-7-amlde (Z-Arg-Arg-MCA) was not. The processing activity, as well as Z-Phe-Arg-MCA hydrolyzing activity, was highly sensitive to cysteine proteinase inhibition, for example, by leupeptin and N[N-3-(trans-carbox-irane-2-carbonyl)-L-leucyl] agmatine (E-64). Furthermore, the enzyme preparation reacted with an antibody against cathepsin L purified from rat kidney. These results indicated that cathep sin L may be involved In the above-mentioned processing of hexokinase.