Comparative studies of two cathepsin B isozymes from porcine spleen. Isolation, polypeptide chain arrangements, and enzyme specificity.
Our previous studies on carbohydrate structures of purified porcine spleen cathepsin B indicated that there are two cathepsin B isozymes, each containing a different carbohydrate (Takahashi, T., Schmidt, P.G., and Tang, J. (1984) J. Biol. Chem. 259, 6059-6062). We have now isolated these two enzymes and carried out a comparative study on their structures and enzymic properties. The major isozyme (CB-I) is a two-chain enzyme (Mr = 28,000) with a light chain (Mr = 5,000) and a heavy chain (Mr = 23,000), whereas the minor enzyme (CB-II) is a single chain enzyme (Mr = 27,000). The NH2-terminal amino acid residues of CB-I were leucine and valine for the light and heavy chain, respectively. However, the NH2-terminal residue of CB-II was not available for automated Edman degradation. In addition, peptide mapping experiments indicated a difference in the primary structure of these two proteins. Despite such structural differences, they are similar in many enzymic properties. CB-I was more catalytically efficient than CB-II toward synthetic substrates, except for the substrate benzoyl-L-arginine beta-naphthylamide for which the relative catalytic efficiency is reversed. Both isozymes degraded glucagon by a dipeptidyl carboxypeptidase activity. Under the same conditions, CB-I was 4-5 times more efficient than CB-II. The results indicate that the cathepsin B isozymes are two separate gene products, but they are similar in enzymic properties.
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002401:Cathepsin B; D002403:Cathepsins / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D005634:Fructose-Bisphosphate Aldolase / Q000378:metabolism; D005934:Glucagon / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008970:Molecular Weight; D010446:Peptide Fragments; D013154:Spleen / Q000201:enzymology*; D013379:Substrate Specificity; D013552:Swine
D000596:Amino Acids; D007527:Isoenzymes; D010446:Peptide Fragments; D005934:Glucagon; D002403:Cathepsins; D002401:Cathepsin B; D005634:Fructose-Bisphosphate Aldolase