Improved purification of cathepsin B1 and cathepsin B2

On the tissue/species dependence of cathepsin B isozymes

Characterization of cathepsin B from buffalo kidney and goat spleen showed the presence of isozymes in case of the goat spleen (GSCB-I and GSCB-II) whereas cathepsin B from buffalo kidney exhibited only one form (BKCB). The molecular weights determined by SDS-PAGE for GSCB-I, GSCB-II, and BKCB were 25.7, 26.6 and 25.5 kDa respectively. The kinetic parameters (Km and Vmax) of GSCB-I showed close similarities with BKCB against alpha-N-benzoyl-DL-arginine-2-napthylamide whereas GSCB-II was closer to the buffalo enzyme with regards to its activity against Z-Arg-Arg-MCA and Z-Phe-Arg-MCA. All the three enzymes had similar sensitivities towards urea, antipain and leupeptin. However, clear differences were observed in the inhibition patterns of the enzyme with iodoacetic acid and iodoacetamide. Differences in the kinetic, immunogenic and some catalytic properties of GSCB-I and II, which had similarities with regard to most of their physico-chemical properties, were considered to be due to the existence of two isozyme forms in goat spleen cathepsin B preparations. Absence of such a multiplicity in forms of the enzyme from buffalo kidney was accordingly attributed to the absence of cathepsin B isozymes in this species. These observations taken together therefore, indicate a probable species/tissue dependence of cathepsin B.

Immunohistochemical studies on enterokinase producing cells in the biliary tract

The activation mechanism of pancreatic enzymes refluxing into the biliary tract in the anomalous arrangement of pancreaticobiliary ducts (APBD) remains unclear. In order to elucidate this activation mechanism, an immunohistochemical examination of both bile ducts and gallbladders was carried out on 20 patients with APBD to determine whether or not enterokinase (EK) producing cells exist in the biliary tract, by employing an avidin-biotin-peroxidase complex (ABC) method using a monoclonal antibody, hek-1. Immunoreactive EK was found in the metaplastic epithelium of the bile duct in 2 patients and the gallbladder in one, suggesting that EK production at the metaplastic epithelium is involved in an activation mechanism of pancreatic enzymes refluxing into the biliary tract. The same study was performed on the gallbladders of 62 patients without APBD, which revealed immunoreactive EK in some parts of the metaplastic epithelium of the gallbladder in 2 patients. Thus, in cases of pancreatic juice refluxing into the biliary tract regardless of the presence of APBD, we can not refute the possibility that refluxed pancreatic enzymes may be at least partly activated by EK produced at the metaplastic epithelium.

Improved purification and some properties of bovine lysosomal carboxypeptidase B

Lysosomal carboxypeptidase B (peptidyl-L-amino-acid hydrolase, EC 3.4.18.1) from bovine spleen purified to apparent homogeneity was found to have a molecular weight of 52 000 in the absence and of 25 000 in the presence of urea, determined by gel filtration, indicating the existence of two subunits of identical size. The amount of approx. 15% carbohydrate estimated after cleavage by endoglycosidase H was shown to be insignificant for enzymatic activity. The isoelectric focusing separated lysosomal carboxypeptidase B into several protein bands - each enzymatically active - with a range of isoelectric points between 4.6 and 5.2. The titration of the sulphydryl group in the active site of the enzyme with the proteinase inhibitor E-64 yielded one thiol group per molecule. A maximum of activation was achieved by the addition of selenocystamine together with dithioerythritol and EDTA in the incubation solution. Under these conditions the carboxypeptidase hydrolyzed benzoylglycylarginine (80 kat/mol enzyme), benzoylarginine amide (38 kat/mol enzyme) and carbobenzoxyglutaryltyrosine (110 kat/mol enzyme). Slight enzymatic activities towards benzoylarginine 2-naphthylamide and benzoylarginine p-nitroanilide could be measured. With the oxidized insulin B chain, lysosomal carboxypeptidase B exhibited only carboxypeptidase activity.

Proteolytic activity of largomycin

Largomycin, an antibiotic and antitumor protein, purified from the culture broth of Streptomyces pluricolorescens, displayed specific proteolytic activity. Pure largomycin did not degrade a number of substrates commonly used for detection of aminopeptidase, endopeptidase and carboxypeptidase activity. Pure largomycin degraded angiotensin II, bradykinin, a few dipeptides and a number of proteins of KB cell plasma membranes. The biological activity and the proteolytic activity of largomycin showed similar temperature-dependent patterns, suggesting that one protein is responsible for both activities. The apoprotein of largomycin, which did not show antibiotic activity, contained the proteolytic activity.

Characterization of two thiol-dependent aminopeptidases partially purified from human placenta

1. Two thiol-dependent aminopeptidases (I and III) were partially purified from the soluble fraction of human placenta. 2. Aminopeptidase I preferred L-alanine-beta-naphthylamide (AlaNA) as substrate at pH 7.0-7.5. It was sensitive to heat and some divalent metal ions (Co2+, Ni2+, Zn2+) but resistant to EDTA, and some amino acids. 3. Aminopeptidase III hydrolysed equally well AlaNA and ArgNA at pH 6.5-7.0. It was markedly suppressed by EDTA and reactivated by Co2+. It was inhibited by heat, some amino acids, benzamadine and puromycin.

Largomycin: preparation, properties, and structure

Largomycin has been purified to homogeneity by chromatography on hydroxylapatite whereby carbohydrate and protease impurities were removed. Largomycin is an acidic protein (pI 4.13, molecular weight 29300) which forms a dimer in phosphate buffer. An N-terminal amino acid sequence analysis from the amino-terminal residue gave, for the first 32 residues, Asp-Ile-Leu-Ile-Ala-Gly-Ala-Thr-Gly-Asn-Val-Gly-Lys-Pro-Leu-Val-Glu-Gly-Leu-Leu - Ala-Ala-Gly-Lys-Pro-Val-Arg-Ala-Leu-Thr-Arg-Asn... The sequence from the carboxyl terminus was -Ala-Ala-Leu-Phe-OH with threonine, valine, and glutamic acid being released upon prolonged digestion. The same amino acid sequences were found for largomycin prepared from either the culture broth or the mycelium of Streptomyces pluricolorescens. The similarities extended to the other physical properties, the antimicrobial activity against Staphylococcus aureus and Sarcina lutea, and the antitumor activity against KB cells. Largomycin inhibits the biosynthesis of DNA and RNA. An iodinated derivative did not bind to KB cells. The antimicrobial activity was lost following ultraviolet irradiation, protection against which was not afforded by p-aminobenzoic acid.

Crystallization and properties of cathepsin B from rat liver

Cathepsin B from rat liver was purified to apparent homogeneity by cell-fractionation, freezing and thawing, acetone treatment, gel filtration, DEAE-Sephadex and CM-Sephadex column chromatography, and was crystallized. The purified enzyme formed spindle-shaped crystals and its homogeneity was proved by disc gel electrophoresis in the presence of sodium dodecyl sulfate and by ultracentrifugal analysis. Its s20,w value was 2.8 S and its relative molecular mass was calculated to be 22,500 (+/- 900) by sedimentation equilibrium analysis. Crystalline cathepsin B was shown to consist of four isozymes with isoelectric points between pH 4.9 and 5.3, the main isozyme having an isoelectric point of pH 5.0. The enzyme was irreversibly inactivated by exposure to weak alkali. The pH optimum was 6.0 with alpha-N-benzoyl-DL-arginine-4-nitroanilide as substrate. Amino acid analysis showed that the enzyme contained hexosamine, glucosamine and galactosamine. Cathepsin B inactivated aldolase, glucokinase, apo-ornithine aminotransferase, and apo-cystathionase, but the rates of inactivation of glucokinase, apo-ornithine aminotransferase, and apocystathionase were lower than that of aldolase. Studies by polyacrylamide gel electrophoresis in the presence and absence of sodium dodecyl sulfate showed that cathepsin B degraded apo-ornithine aminotransferase to two polypeptide chains differing in relative molecular mass and electrophoretic mobility.

Carboxypeptidase B activity of cultured skin fibroblasts and relationship to cystic fibrosis

Enzyme activity against hippuryl-L-arginine was studied in cultured skin fibroblasts from controls and cystic fibrosis patients. The enzyme had a lysosomal distribution and an acid optimum of pH 4.5 with little or no activity present above pH 7.0. Dithiothreitol was required for full activity and the kinetics of thiol activation were different for the control and cystic fibrosis enzyme. The properties and lysosomal distribution of the enzyme indicated that it was a carboxypeptidase B. Substrate affinity, thermolability, pH stability, the fall and rise in activity with subculture, the cyclical pattern of activity through serial passage and the level of activity were similar for the control and cystic fibrosis enzyme.

Separation of cathepsin B1 and related enzymes from rat skeletal muscle

Rat muscle was extracted at pH 4 and submitted to gel-filtration on Sephadex G-75 and to chromatography on DEAE-Sephadex. Gel-filtration gave a large peak of activity towards Bz-Arg-NNap with an estimated molecular weight of 25,500. Activity towards Bz-Arg-NH2 was present in this peak and in another peak of molecular weight 45,000. The second peak also hydrolysed benzoyl-glycyl-L-arginine. DEAE-Sephadex gave five peaks of Bz-Arg-NNap hydrolysing activity; all showed thiol dependence. Peaks III, IV and V hydrolysed Z-Ala-Arg-Arg-NNap-OMe rapidly; they also inactivated aldolase and were strongly inhibited by leupeptin. They are probably isoenzymes of cathepsin B1. Peak I showed these properties to a relatively small extent. 7-(N-Benzoyl-DL-argininamide)-4-methylcoumarin appears to be an alternative substrate for cathepsin B1; it was hydrolysed also by peak I, but relatively less rapidly. Peaks I and II were inhibited more than peaks III, IV and V by a muscle extract. Total activity of the Bz-Arg-NH2-hydrolysing enzyme in extensor digitorum longus muscle increased after denervation.

Cathepsin L. A new proteinase from rat-liver lysosomes

1. Cathepsin L was purified from rat liver lysosomes by cell fractionation, osmotic disruption of the lysosomes in the lysosomal mitochondrial pellet, gel filtration of the lysosomal extract and chromatography on CM-Sephadex. 2. Cathepsin L is a thiol proteinase and exists in several multiple forms visible on the disc electropherogram. By polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate its molecular weight was found to be 23000-24000. The isoelectric points of the multiple forms of cathepsin L extended from pH 5.8-6.1 ascertained by analytical isoelectric focusing. 3. Using various protein substrates, cathepsin L was found to be the most active endopeptidase from rat liver lysosomes acting at pH 6-7. In contrast to cathepsin B1, its capability of hydrolyzing N-substituted derivatives of arginine is low and it does not split esters. 4. Greatest activity is obtained close to pH 5.0 with 70-90% of maximal activity at pH 4.0 and pH 6.0 and 30-40% at pH 7.0. 5. The enzyme is strongly inhibited by leupeptin and the chloromethyl ketone of tosyl-lysine. Leupeptin acts as a pseudo-irreversible inhibitor. 6. The enzyme is stable for several months at slightly acid pH values in the presence of thiol compounds in a deep-frozen state.

On the specificity of bovine spleen cathepsin B2

The specificity of bovine spleen cathepsin B2 has been investigated by means of some natural oligo- and polypeptides, i.e. glucagon, melittin, insulin A and B chain, bradykinin, angiotensin I and II, oxytocin ACTH, clupein and salmin. The enzyme is primarily a carboxypeptidase which hydrolyzes peptide linkages of most amino acids common to proteins. In addition, cathepsin B2 displays amidase and esterase activity without requiring a free carboxyl group. The main pH optimum is between 4 and 5, in some cases higher.