Characteristics of protease synthesis in Bacteroides splanchnicus NCTC 10825

Studies to determine the physiological and nutritional characteristics of protease synthesis by Bacteroides splanchnicus NCTC 10825 showed that the proteases were constitutive and cell-associated during exponential growth in batch culture. As growth slowed and the bacteria entered the stationary phase, proteases that had accumulated intracellularly were released into the culture media. In continuous cultures, [dilution rate (D)=0.03 h^–1 to D=0.29 h^–1], protease activity was completely cell-bound and maximal during nitrogen-limited growth at high dilution rates. The proteases hydrolysed a relatively restricted range of protein substrates including casein, azocasein and gelatine (comparative maximum rates of hydrolysis were 1.0, 4.1 and 2.7 units mg^–1 protein respectively). B. splanchnicus proteases exhibited arylamidase activities against leucine p-nitroanilide, valylalanine p-nitroanilide and glycylproline p-nitroanilide. Inhibition experiments indicated that the bacterium produced a mixture of serine, thiol and, possibly, metalloproteases. Protease activities were affected by reducing agents and divalent metal ions. Mercaptoethanol at 1 mm was slightly stimulatory; however, dithiortheitol and dithioerythritol (each 10 mm) respectively inhibited protease activities by 91% and 100%. Calcium ions (5 mm) stimulated protease activity by 30%, whereas Mn²⁺ and Mg²⁺ had little or no effect. Protease and arylamidase activities had neutral to alkaline pH optima. Together, these results show that with respect to the types of protease formed and the physiology of the process, B. splanchnicus proteolysis is similar in many respects to that occurring in species belonging to the B. fragilis group. Correspondence to: G. T. Macfarlane     

Purification and characterization of a trypsin-like enzyme with fibrinolytic activity present in the abdomen of horn fly, Haematobia irritans irritans (Diptera: Muscidae)

This work describes the purification and characterization of a trypsin-like enzyme with fibrinolytic activity present in the abdomen of Haematobia irritans irritans (Diptera: Muscidae). The enzyme was purified using a one-step process, consisting of affinity chromatography on SBTI-Sepharose. The purified protease showed one major active proteinase band on reverse zymography with 0.15% gelatin, corresponding to a molecular mass of 25.5 kDa, with maximum activity at pH 9.0. The purified trypsin-like enzyme preferentially hydrolyzed synthetic substrates with arginine residue at the P1 position. The K _m values determined for three different substrates were 1.88 × 10^–4, 1.28 × 10^–4, and 1.40 × 10^–4 M for H--benzoyl-Ile-Glu-Gly-Arg-p-nitroanilide (S2222), dl-Ile-Pro-Arg-p-nitroanilide (S2288), and DL-Phe-Pip-Arg-p-nitroanilide (S2238), respectively. The enzyme was strongly inhibited by typical serine proteinase inhibitors such as SBTI (soybean trypsin inhibitor, K _i = 0.19 nM) and BuXI (Bauhinia ungulata factor Xa inhibitor, K _i = 0.48 nM), and less inhibited by LDTI (leech-derived tryptase inhibitor, K _i = 1.5 nM) and its variants LDTI 2T and 5T (0.8 and 1.5 nM, respectively). The most effective inhibitor for this protease was r-aprotinin (r-BPTI) with a K _i value of 39 pM. Synthetic serine protease inhibitors presented only weak inhibition, e.g., benzamidine with K _i = 3.0 × 10^–4 M and phenylmethylsulfonyl fluoride (PMSF) showed traces of inhibition. The purified trypsin-like enzyme also digested natural substrates such as fibrinogen and fibrin net. The protease showed higher activity against fibrinogen and fibrin than did bovine trypsin. These data suggest that the proteolytic enzyme of H. irritans irritans is more specific to proteins from blood than are the vertebrate digestive enzymes. This enzyme's characteristics may be an adaptation resulting from the feeding behavior of this hematophagous insect.     

Intracellular serine protease-4, a new intracellular serine protease activity from Bacillus subtilis

A previously undiscovered intracellular serine protease activity, which we have called intracellular serine protease-4, was identified in extracts of stationary Bacillus subtilis cells, purified 260 fold from the cytoplasmic fraction, and characterized. The new protease was stable and active in the absence of Ca²⁺ ions and hydrolyzed azocasein and the chromogenic substrate carbobenzoxy-carbonyl-alanyl-alanyl-leucyl-p-nitroanilide, but not azocollagen or a variety of other chromogenic substrates. The protease was strongly inhibited by phenylmethylsulfonylfluoride, chymostatin and antipain, but not by chelators, sulfhydryl-reactive agents or trypsin inhibitors. Its activity was stimulated by Ca²⁺ ions and gramicidin S; its pH and temperature optima were 9.0 and 37°C, respectively. Although intracellular serine protease-4 was immunochemically distinct from intracellular serine protease-1, it was absent from a mutant in which the gene encoding the latter was disrupted.     

Purification and characterization of fibrinolytic metalloprotease from Perenniporia fraxinea mycelia

In this study we purified and characterized a fibrinolytic protease from the mycelia of Perenniporia fraxinea. The apparent molecular mass of the purified enzyme was estimated to be 42 kDa by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), fibrin zymography and size exclusion using fast protein liquid chromatography (FPLC). The first 20 amino acid residues of the N-terminal sequence were ASYRVLPITKELLPPEFFVA, which shows a high degree of similarity with a fungalysin metallopeptidase from Coprinopsis cinerea. The optimal reaction pH value and temperature were pH 6.0 and 35–40 °C, respectively. Results for the fibrinolysis pattern showed that the protease rapidly hydrolyzed the fibrin α-chain followed by the β-chain. The γ–γ chains were also hydrolyzed, but more slowly. The purified protease effectively hydrolyzed fibrinogen, preferentially digesting the Aα-chains of fibrinogen, followed by Bβ- and γ-chains. We found that protease activity was inhibited by Cu²⁺, Fe³⁺, and Zn²⁺, but enhanced by the additions of Mn²⁺, Mg²⁺ and Ca²⁺ metal ions. Furthermore, the protease activity was inhibited by EDTA, and it was found to exhibit a higher specificity for the chromogenic substrate S-2586 for chymotrypsin, indicating that the enzyme is a chymotrypsin-like metalloprotease. The mycelia of P. fraxinea may thus represent a source of new therapeutic agents to treat thrombosis.     

Purification and characterization of x-prolyl-dipeptidyl aminopeptidase from Lactococcus lactis subsp. cremoris NRRL 634

Summary An X-prolyl-dipeptidylaminopep tidase (Pep-XP) was purified from the crude intracellular extract of Lactococcus lactis subsp. cremoris NRRL 634 by ion exchange and gel filtration chromatographies. The enzyme was purified 80-fold with a recovery of 6%, and appeared as a single band with a molecular weight of about 80 kDa on polyacrylamide gel electrophoresis with sodium dodecyl sulphate (SDS-PAGE). The peptidase showed its maximal activity on arginyl-proline-p-nitroanilide at pH 7.0 and at a temperature of 45 °C, although there was a good activity of Pep-XP in the pH range of 5.5–7.0 and temperatures between 40 and 50 °C. The Michaelis constant (K _m) and the maximum reaction velocity (V _max) values were 0.92 mM and 7.9 U/mg protein min, respectively. The activity of Pep-XP was completely inhibited by phenylmethanesulphonyl fluoride, an inhibitor of serine peptidases, and metal chelators had little effect on enzyme activity. The purified enzyme hydrolyzed synthetic substrates whose structure is X-Pro-Y like Lys-Pro-pNA, but did not hydrolyse Pro-pNA or azocasein, showing that the enzyme did not have aminopeptidase or endopeptidase activities.     

Purification and Characterization of Aminopeptidase from Euphausia superba

Krill aminopeptidase was purified about, 1,100-fold from an extract of Euphausia superba with DEAE-cellulose column chromatography, Toyopearl HW55, and hydroxyapatite column chromatography. The final preparation was electrophoretically homogeneous. The molecular weight was determined to be 140,000 by gel filtration and SDS-polyacrylamide disc gel electrophoresis. The optimum pH and optimum temperature were 8.4 and 45°C respectively. Krill aminopeptidase was inhibited by EDTA, Hg^{+ +} and amastatin, and partially by bestatin, and was activated by Co ^{+ +}. Alanyl-p-nitroanilide was hydrolyzed faster than leucyl-p-nitroanilide. Alanyl peptides (di-, tri-, tetra- and hexa-alanyl peptide) were hydrolyzed very fast.

These results suggest that krill aminopeptidase is an alanine aminopeptidase which is activated by cobaltous ion.     

Purification and properties of a fibrinogenase from the venom of Naja nigricollis

A fibrinogenolytic proteinase from the venom of Naja nigricollis was purified by chromatography on Bio-Rex 70 and Phenyl-Sepharose. The purified enzyme, designated proteinase F1, was homogeneous by the criterion of SDS-polyacrylamide gel electrophoresis, and consisted of a single chain with a molecular weight of 58 000. Purified proteinase F1 had approximately 15-fold more proteinase activity than the crude venom, based on its ability to inactive α₂-macroglobulin. The enzyme acted on only the Aα-chain of fibrinogen and left the Bβ- and γ-chains intact. The pH optimum for this fibrinogenolytic activity was in the range of pH 8 to 10. In addition to its activity on fibrinogen, proteinase F1 was active on α₂-macroglobulin and fibronectin, but did not degrade casein, hemoglobin or bovine serum albumin. The enzyme was not inhibited by inhibitors of serine proteinases, cysteine proteinases or acid proteinases, but only by the metalloproteinase inhibitor, EDTA. The inhibition by EDTA could be prevented by Zn²⁺, but not by Ca²⁺ or Mg²⁺.     

Expression, purification and characterization of Gloydius shedaoensis venom gloshedobin as Hsp70 fusion protein in Pichia pastoris

Gloshedobin, a thrombin-like enzyme from the venom of Gloydius shedaoensis was expressed as Hsp70 fusion protein from the construct pPIC9K/hsp70-TLE in the yeast Pichia pastoris. By fusing gloshedobin to the C-terminus of Hsp70, an expression level of 44.5 mg Hsp70-gloshedobin per liter of culture was achieved by methanol induction. The fusion protein secreted in the culture medium was conveniently purified by two chromatographic steps: Q-Sepharose FF and Superdex 200. The purified enzyme had an apparent molecular mass of 98 kDa according to SDS–PAGE analysis, and exhibited fibrinogenolytic activity that preferentially degraded fibrinogen α-chain. The enzyme also degraded fibrinogen β-chain to a lesser extent, while showing no degradation toward the γ-chain. A fibrinogen clotting activity of 499.8 U/mg was achieved by the enzyme, which is within the range reported for other thrombin-like enzymes. Hsp70-gloshedobin had strong esterase activity toward the chromogenic substrate Nα-p-tosyl-Gly-Pro-Arg-p-nitroanilide, and this activity was optimal at pH 7.5 and 50 °C, and was completely inhibited by PMSF, but not by EDTA. We concluded that Hsp70 has no effect on the physiochemical and biochemical properties of gloshedobin. Although applying a fusion partner with very big molecular weight is unusual, Hsp70 proved its advantage in soluble expression of gloshedobin without affecting its fibrinogenolytic activity. And this positive result may provide an alternative strategy for the expression of thrombin-like enzymes in microbial system.     

Purification and Properties of a Type II-like Dipeptidyl Peptidase from the Ruminal Peptidolytic Bacterium,Prevotella albensis M384

A dipeptidyl peptidase which hydrolyses the synthetic dipeptidyl peptidase (DPP) substrate, Ala₂- p -nitroanilide, was purified 193-fold from the ruminal peptidolytic bacterium, Prevotella albensis M384. The enzyme was a homodimer of molecular mass 91 kDa. Its activity against Ala₂- p -nitroanilide had optimal pH and temperature of 7.2 and 40°C respectively. Enzyme activity was inhibited by the serine protease inhibitors, PMSF and dichloroisocoumarin, but not by inhibitors of other categories of proteases. Synthetic substrates for DPP-1 (GlyArg- p -nitroanilide, GlyArg-4-methoxy-naphthylamide), DPP-3 (ArgArg-4-methoxynaphthylamide) and DPP-4 (GlyPro-4-methoxynaphthylamide) or for leucine or alanine aminopeptidase were not hydrolysed, nor were di- or tripeptides. N-Acetyl-Ala₂- p -nitroanilide was not hydrolysed. Oligopeptides with Ala, Ile, Ser or Val adjacent to the N-terminal amino acid were all hydrolysed, while peptides with basic or acidic residues in the same position were not. The purified DPP from P. albensis is therefore most similar in its catalytic properties to mammalian DPP-2.     

Purification and properties of an alkaline protease of <Emphasis Type="Italic">Aspergillus clavatus</Emphasis>

An extracellular alkaline serine protease has been purified from a strain of Aspergillus clavatus, to apparent homogeneity, by ammonium sulfate precipitation and chromatography on Sephadex G-75. Its molar mass, estimated by SDS-PAGE, was 35 kDa. Maximum protease activity was observed at pH 9.5 and 40°C. The enzyme was active between pH 6.0 and 11.0 and was found to be unstable up to 50°C. Calcium at 5 mM increased its thermal stability. The protease was strongly inhibited by PMSF and chymostatin as well as by SDS, Tween 80 and carbonate ion. Substrate specificity was observed with N-p-Tos-Gly-Pro-Arg-p-nitroanilide and N-Suc-Ala-Ala-Ala-p-nitroanilide being active substates. Parts of the amino acid sequence were up to 81% homologous with those of several fungal alkaline serine proteases.     

Hydrolysis of β-Galactosyl Ester Linkage by β-Galactosidases

p-Hydroxybenzoyl β-galactose (pHB-Gal) was synthesized chemically to examine the hydrolytic activity of β-galactosyl ester linkage by β-galactosidases. The enzyme from Penicillium multicolor hydrolyzed the substrate as fast as p-nitrophenyl β-galactoside (pNP-Gal), a usual substrate with a β-galactosidic linkage. The enzymes from Escherichia coli and Aspergillus oryzae hydrolyzed pHB-Gal with almost the same rates as pNP-Gal. The enzymes from Bacillus circulans, Saccharomyces fragilis, and bovine liver showed much lower activities. pH-activity profiles, inhibition analysis, and kinetic properties of the enzymic reaction on pHB-Gal suggested that β-galactosidase had only one active site for hydrolysis of both galactosyl ester and galactoside. The Penicillium enzyme hydrolyzed pHB-Gal in the presence of H₂ ¹⁸O to liberate galactose containing ¹⁸O. This result suggests the degradation occurs between the anomeric carbon and an adjacent O atom in the ester linkage of pHB-Gal.     

An in silico approach to understand the structure–function properties of a serine protease (Bacifrinase) from Bacillus cereus and experimental evidence to support the interaction of Bacifrinase with fibrinogen and thrombin

Microbial fibrinogenolytic serine proteases find therapeutic applications in the treatment of thrombosis- and hyperfibrinogenemia-associated disorders. However, analysis of structure–function properties of an enzyme is utmost important before its commercial application. In this study, an attempt has been made to understand the structure of a fibrinogenolytic protease enzyme, “Bacifrinase” from Bacillus cereus strain AB01. From the molecular dynamics trajectory analysis, the modelled three-dimensional structure of the protease was found to be stable and the presence of a catalytic triad made up of Asp102, His83 and Ser195 suggests that it is a serine protease. To understand the mechanism of enzyme–substrate and enzyme–inhibitor interactions, the equilibrated protein was docked with human fibrinogen (the physiological substrate of this enzyme), human thrombin and with ten selective protease inhibitors. The Bacifrinase–chymostatin interaction was the strongest among the selected protease inhibitors. The serine protease inhibitor phenyl methane sulphonyl fluoride was found to interact with the Ser134 residue of Bacifrinase. Furthermore, protein–protein docking study revealed the fibrinogenolytic property of Bacifrinase and its interaction with Aα-, Bβ- and Cγ-chains human fibrinogen to a different extent. However, biochemical analysis showed that Bacifrinase did not hydrolyse the γ-chain of fibrinogen. The in silico and spectrofluorometric studies also showed interaction of Bacifrinase with thrombin as well as fibrinogen with a Kd value of 16.5 and .81 nM, respectively. Our findings have shed light on the salient structural features of Bacifrinase and confirm that it is a fibrinogenolytic serine protease.     

Aminopeptidases in the Acidic Fraction of the Yeast Autolysate

Two aminopeptidases, I and II, were found in the acidic fraction of the yeast autolysate, adsorbed on DEAE-cellose and DEAE-Sephadex A&50. Aminopeptidase I was purified as a single protein with a molecular weight of 200,000. The enzyme required Zn for its activity and hydrolyzed dipeptides, and a polypeptide (glucagon). It also hydrolyzed amides, naphthylamides and the p-nitroanilide of amino acids. The enzyme was strongly inhibited by sulfhydryl reagents. Aminopeptidase II seemed also to be a metal enzyme with a molecular weight of 34,000. The enzyme hydrolyzed the dipeptide and tetrapeptide but not leucine-p-nitroanilide.     

Thermostable alkaline protease produced by Bacillus thermoruber — a new species of Bacillus

Summary The proteolytic activity produced by a new species of Bacillus isolated in our laboratory was investigated. This enzyme was purified to homogeneity from cell-free culture liquids of B. thermoruber. The purification procedure included ion-exchange chromatography on DEAE-Sephadex A-50 and -casein agarose affinity chromatography. The protease consists of one polypeptide chain with a molecular weight of 39000±800. the isoelectric point was 5.3; the optimum pH and temperature for proteolytic activity (on casein) was found to be pH 9 and 45°C respectively. Enzyme activity was inhibited by PMSF and EDTA. The stability was considerably increased by addition of Ca²⁺, and the protease exhibited a relatively high thermal stability. The alkaline protease shows a preference for leucine in the carboxylic side of the peptide bond of the substrate. The K _m value for benzyloxycarbonyl-Ala-Ala-Leu-p-nitroanilide was 2.5 mM.     

Purification and characterization of a fibrinolytic subtilisin-like protease of Bacillus subtilis TP-6 from an Indonesian fermented soybean, Tempeh

We have isolated a bacterium (TP-6) from the Indonesian fermented soybean, Tempeh, which produces a strong fibrinolytic protease and was identified as Bacillus subtilis. The protease (TPase) was purified to homogeneity by ammonium sulfate fractionation and octyl sepharose and SP sepharose chromatography. The N-terminal amino acid sequence of the 27.5 kDa enzyme was determined, and the encoding gene was cloned and sequenced. The result demonstrates that TPase is a serine protease of the subtilisin family consisting of 275 amino acid residues in its mature form. Its apparent K _m and V _max for the synthetic substrate N-succinyl-Ala-Ala-Pro-Phe-pNA were 259 μM and 145 μmol mg⁻¹ min⁻¹, respectively. The fibrinogen degradation pattern generated by TPase as a function of time was similar to that obtained with plasmin. In addition, N-terminal amino acid sequence analysis of the fibrinogen degradation products demonstrated that TPase cleaves Glu (or Asp) near hydrophobic acids as a P1 site in the α- and β-chains of fibrinogen to generate fragments D′, E′, and D′ similar to those generated by plasmin. On plasminogen-rich fibrin plates, TPase did not seem to activate fibrin clot lysis. Moreover, the enzyme converted the active plasminogen activator inhibitor-1 to the latent form.Seong-Bo Kim and Dong-Woo Lee contributed equally to the work.     

Molecular and biochemical characterization of an extracellular serine-protease from <Emphasis Type="Italic">Vibrio metschnikovii</Emphasis> J1

A protease-producing bacterium was isolated from an alkaline wastewater of the soap industry and identified as Vibrio metschnikovii J1 on the basis of the 16S rRNA gene sequencing and biochemical properties. The strain was found to over-produce proteases when it was grown at 30°C in media containing casein as carbon source (14,000 U ml⁻¹). J1 enzyme, the major protease produced by V. metschnikovii J1, was purified by a three-step procedure, with a 2.1-fold increase in specific activity and 33.3% recovery. The molecular weight of the purified protease was estimated to be 30 kDa by SDS-PAGE and gel filtration. The N-terminal amino acid sequence of the first 20 amino acids of the purified J1 protease was AQQTPYGIRMVQADQLSDVY. The enzyme was highly active over a wide range of pH from 9.0 to 12.0, with an optimum at pH 11.0. The optimum temperature for the purified enzyme was 60°C. The activity of the enzyme was totally lost in the presence of PMSF, suggesting that the purified enzyme is a serine protease. The kinetic constants K _m and K _cat of the purified enzyme using N-succinyl-l-Ala-l-Ala-l-Pro-l-Phe-p-nitroanilide were 0.158 mM and 1.14 × 10⁵ min⁻¹, respectively. The catalytic efficiency (K _cat /K _m) was 7.23 × 10⁸ min⁻¹ M⁻¹. The enzyme showed extreme stability toward non-ionic surfactants and oxidizing agents. In addition, it showed high stability and compatibility with some commercial liquid and solid detergents. The aprJ1 gene, which encodes the alkaline protease from V. metschnikovii J1, was isolated, and its DNA sequence was determined. The deduced amino acid sequence of the preproenzyme differs from that of V. metschnikovii RH530 detergent-stable protease by 12 amino acids, 7 located in the propeptide and 5 in the mature enzyme.     

Purification and properties of an alkaline protease from alkalophilic Bacillus sp. KSM-K16

Alkaline protease (EC 3.4.21.14) activity, suitable for use in detergents, was detected in the alkaline culture medium of Bacillus sp. KSM-K16, which was originally isolated from soil. The enzyme, designated M protease, was purified to homogeneity from the culture broth by column chromatographies. The N-terminal amino acid sequence was Ala-Gln-Ser-Val-Pro-Trp-Gly-Ile-Ser-Arg-Val-Gln-Ala-Pro-Ala-Ala-His-Asn-Arg-Gly-Leu-Thr-Gly. The molecular mass of the protease was 28 kDa, and its isoelectric point was close to pH 10.6. Maximum activity toward casein was observed at 55°C and at pH 12.3 in 50 mM phosphate/NaOH buffer. The activity was inhibited by phenylmethylsulfonyl flouride and chymostatin. The enzyme was very stable in long-term incubation with liquid detergents at 40°C. The enzyme cleaved the oxidized insulin B chain initially at Leu¹⁵-Tyr¹⁶ and efficiently at ten more sites. Among various oligopeptidyl p-nitro-anilides (pNA) tested, N-succinyl-Ala-Ala-Pro-Phe-pNA was efficiently hydrolyzed by M protease. M protease was precipitated in (NH₄)₂SO₄-saturated acetate buffer (pH 5.0) as plank-like cyrstals.     

Purification,biochemical, and structural characterization of a novel fibrinolytic enzyme from Mucor subtilissimus UCP 1262

Fibrinolytic proteases are enzymes that degrade fibrin. They provide a promising alternative to existing drugs for thrombolytic therapy. A protease isolated from the filamentous fungus Mucor subtilissimus UCP 1262 was purified in three steps by ammonium sulfate fractionation, ion exchange, and molecular exclusion chromatographies, and characterized biochemically and structurally. The purified protease exhibited a molecular mass of 20 kDa, an apparent isoelectric point of 4.94 and a secondary structure composed mainly of α-helices. Selectivity for N-succinyl-Ala–Ala–Pro–Phe-p-nitroanilide as substrate suggests that this enzyme is a chymotrypsin-like serine protease, whose activity was enhanced by the addition of Cu²⁺, Mg²⁺, and Fe²⁺. The enzyme showed a fibrinolytic activity of 22.53 U/mL at 40 °C and its contact with polyethylene glycol did not lead to any significant alteration of its secondary structure. This protein represents an important example of a novel fibrinolytic enzyme with potential use in the treatment of thromboembolic disorders such as strokes, pulmonary emboli, and deep vein thrombosis.

     

Purification and Partial Characterization of a Prolyl-Dipeptidyl Aminopeptidase from Lactobacillus helveticus CNRZ 32

X-prolyl-dipeptidyl aminopeptidase, which hydrolyzed Gly-Pro-p-nitroanilide (relative activity [RA] = 100%) and Arg-Pro-p-nitroanilide (RA, 130%), was purified to homogeneity from the cell extract of Lactobacillus helveticus CNRZ 32. The enzyme also hydrolyzed Ala-Pro-Gly (RA, 11%) and Ala-Ala-p-nitroanilide (RA, 2%) but was not active on Ala-Leu-Ala, dipeptides, and endopeptidase and carboxypeptidase substrates. The enzyme was purified 145-fold by streptomycin sulfate precipitation, ammonium sulfate fractionation, and a series of column chromatographies on DEAE-cellulose, arginine-Sepharose 4B, and glycyl-prolyl-AH-Sepharose 4B. The purified enzyme appeared as a single band on native polyacrylamide gel and sodium dodecyl sulfate-polyacrylamide gel electrophoreses and had a molecular weight of 72,000. Optima for activity by the purified enzyme were pH 7.0 and 40°C. The enzyme was incubated at 40°C for 15 min with various metal ions. It was activated by Mg²⁺ (2.5 mM), Ca²⁺ (0.1 to 2.5 mM), Na⁺ (10 to 50 mM), and K⁺ (10 to 50 mM) and was inhibited by Hg²⁺ (0.1 to 2.5 mM), Cu²⁺ (0.1 to 2.5 mM), and Zn²⁺ (0.1 to 2.5 mM). Enzyme activity was partially inhibited by EDTA (1.0 mM, 20 h at 40°C), 1,10-phenanthroline (1.0 mM, 15 min at 40°C), phenylmethylsulfonyl fluoride (1.0 mM), N-ethylmaleimide (1.0 mM), and iodoacetate (1.0 mM). It was completely inhibited by diisopropyl fluorophosphate (1.0 mM, 2 h at 40°C) and p-chloromercuribenzoate (1.0 mM, 15 min at 40°C). The enzyme was not affected by dithioerythritol (1.0 to 10 mM).     

Partial purification and characterization of endoproteinases from senescing barley leaves

Two major endoproteinases were purified from senescing primary barley leaves. The major enzyme (EP₁) appeared to be a thiol proteinase and accounted for about 85% of the total proteolytic activity measured in vitro. This proteinase was purified 5,800-fold and had a molecular weight of 28,300. It was highly unstable in the absence of dithiothreitol or at a pH greater than 7.5. Leupeptin, at a concentration of 10 micromolar, inhibited this enzyme 100%. A second proteinase (EP₂) was purified approximately 50-fold and had a molecular weight of 67,000. It was inhibited 20% by 1 millimolar dithiothreitol and 50% by 1 millimolar phenylmethyl sulfonylfluoride. EP₂ contributed about 15% of the total proteolytic activity measured in vitro. Both proteinases hydrolyzed a variety of artificial and protein substrates, and both had pH optima of 5.5 to 5.7 when either azocasein or [¹⁴C]ribulose-1,5-bisphosphate carboxylase ([¹⁴C]RuBPCase) was the substrate. The thiol endoproteinase hydrolyzed azocasein linearly but hydrolyzed [¹⁴C]RuBPCase biphasically. A third endoproteinase (EP₃), not detected by standard proteolytic assays, was observed when [¹⁴C]RuBPCase was the substrate.