Cathepsins B and H from porcine spleen. Purification, polypeptide chain arrangements, and carbohydrate content.

Procedures for the purification of cathepsins B and H from porcine spleens have been described. The purified porcine cathepsin B (Mr = 27,000) is predominantly a two-chain enzyme with a heavy chain (Mr = 22,000) and a light chain (Mr = 5,000). It also contains two minor forms of cathepsin B with different chain structures. Porcine cathepsin H is a single-chain enzyme with a molecular weight of 25,000. The carbohydrate analyses showed that these enzymes were glycoproteins. A glycopeptide containing 3 amino acids, 2 glucosamines, and 6 mannoses was isolated from cathepsin H. Proton NMR studies revealed that it contained a mixture of 4 high mannose-type of oligosaccharides characteristic of those found on lysosomal enzymes. The carbohydrate of cathepsin B consisted of a single residue of glucosamine and trace mannose. This sugar content is in agreement with the finding that about 80% of the porcine spleen cathepsin B contained a single N-acetylglucosamine while 20% of the enzyme contained a 5-sugar oligosaccharide (Takahashi, T., Schmidt, P. G. and Tang, J. (1984) J. Biol. Chem. 259, 6059-6062). Thus, the studies on carbohydrate contents also indicated the good purity of the enzymes.