Purification and characterization of chymosin and pepsin from kid

The objective of this work was to study the characteristics of the gastric aspartic proteinases chymosin and pepsin which are constituents of the kid rennet. The two enzymes were extracted from abomasal tissue of one kid from a local indigenous breed, separated from each other by DEAE-cellulose chromatography and then were purified by gel filtration and anion-exchange chromatography. The molecular weights of the purified kid chymosin and pepsin as determined by gel filtration were 36 kDa and 40 kDa respectively. The isoelectric point of kid chymosin was as multiple forms of 3–6 zones at pH 4·6–5·1, while that of kid pepsin was at pH [les ]3·0. Kid pepsin contained 0·37 molecules phosphorous per molecule and was totally inhibited by 5 μM pepstatin A, being more sensitive than kid chymosin. Both enzymes were almost equally as proteolytic as calf chymosin on total casein at pH 5·6. Kid pepsin activity was more pH and temperature dependent than kid chymosin activity. In comparison with the calf chymosin temperature sensitivity, the order of increased sensitivity was: calf chymosin <kid chymosin <kid pepsin.

Features of the acid protease partition in aqueous two-phase systems of polyethylene glycol–phosphate: Chymosin and pepsin

The partitioning of chymosin (from Aspergilus niger) and pepsin (from bovine stomach) was carried out in aqueous-two phase systems formed by polyethyleneglycol-potassium phosphate. The effects of polymer concentration, molecular mass and temperature were analysed. The partition was assayed at pH 7.0 in systems of polyethyleneglycol of molecular mass: 1450, 3350, 6000 and 8000. Both proteins showed high affinity for the polyethyleneglycol rich phase. The increase of polyethyleneglycol concentration favoured the protein transfer to the top phase, suggesting an important protein-polymer interaction. Polyethyleneglycol proved to have a stabilizing effect on the chymosin and pepsin, increasing its protein secondary structure. This finding agreed with the enhancement of the milk clotting activity by the polyethyleneglycol. The method appears to be suitable as a first step for the purification of these proteins from their natural sources.

Isolation, purification and characterization of chymosin from riverine buffalo (Bubalos bubalis)

Chymosin, an aspartyl proteinase, is used for curdling of milk and manufacture of cheese. We report the purification and the physicochemical properties of chymosin isolated from the abomasal tissue of buffalo calves. The enzyme preparation extracted from buffalo abomasal tissues could be purified 29-fold using anion exchange and gel filtration chromatography. The molecular weight of the purified enzyme was 35.6 kDa on SDS-PAGE. Partial N-terminal amino acid sequence of the first eight amino acid sequences of buffalo chymosin was identical to the first eight amino acid sequences of cattle chymosin. Buffalo chymosin exhibited a skewed bell-shaped stability profile as a function of temperature with maximum activity near 55 degrees C. Milk clotting activity decreased gradually as pH increased. The enzyme became completely inactive, however, above pH 7.0. The ratio of milk clotting to proteolytic activity was 3.03. When compared with cattle chymosin, there were subtle differences in the stability and relative proteolytic activity of buffalo chymosin.

High recovery of prochymosin from inclusion bodies using controlled air oxidation

Refolding of proteins from inclusion bodies is a field of increasing interest for obtaining large amounts of active enzymes. Consequently, the development of inexpensive and scalable processes is required. This is particularly challenging in the case of eukaryotic proteins containing cysteines, which may form disulfide bonds in the native active protein. Previous studies have shown that the formation of disulfide bonds is essential for the refolding of prochymosin. In this work we demonstrate that air oxidation can be efficiently used for the refolding of prochymosin and that 48% of the unfolded protein can be recovered as active enzyme at a final protein concentration of 0.8 mg/ml. Refolding of the protein strictly correlates with the change in pH of the refolding solution. We were able to follow the degree of oxidative renaturation of the prochymosin by simply measuring pH. Thus, the scaling up of the refolding system under controlled conditions was easily achieved. Analyses of different substances as folding aids indicate that the use of L-arginine or neutral surfactants improves the recovery of active protein up to 67% of the initial protein. The overall results indicate that prochymosin can be efficiently and inexpensively refolded with high yields by controlled air oxidation.

Isolation of milk-clotting enzyme from transgenic sheep milk and its comparison with calf chymosin

Technology for preparation of chymosin from milk of transgenic sheep has been elaborated. Purification of the preparation by ion-exchange chromatography on aminosilochrom and biospecific chromatography on bacitracin-Sepharose yielded homogeneous active enzyme. Hydrolysis of protein substrates (hemoglobin, BSA, and sodium caseinate) by the transgenic sheep chymosin and stability of the enzyme at various values of pH were studied. Judging by the amino acid composition, the N-terminal sequence involving six amino acid residues, molecular mass, stability at various pH values, and the catalytic activity against the protein substrates, the transgenic sheep chymosin is identical to calf chymosin.

Oxidative refolding of recombinant prochymosin

The disulphide-coupled refolding of recombinant prochymosin from Escherichia coli inclusion bodies was investigated. Prochymosin solubilized from inclusion bodies is endowed with free thiol groups and disulphide bonds. This partially reduced form undergoes renaturation more efficiently than the fully reduced form, suggesting that some native structural elements existing in inclusion bodies and remaining after denaturation function as nuclei to initiate correct refolding. This assumption is supported by the finding that in the solubilized prochymosin molecule the cysteine residues located in the N-terminal domain of the protein are not incorrectly paired with the other cysteines in the C-terminal domain. Addition of GSH/GSSG into the refolding system facilitates disulphide rearrangement and thus enhances renaturation, especially for the fully reduced prochymosin. Based on the results described in this and previous papers [Tang, Zhang and Yang (1994) Biochem. J. 301, 17-20], a model to depict the refolding process of prochymosin is proposed. Briefly, the refolding process of prochymosin consists of two stages: the formation and rearrangement of disulphide bonds occurs at the first stage in a pH11 buffer, whereas the formation and adjustment of tertiary structure leading to the native conformation takes place at the second stage at pH8. The pH11 conditions help polypeptides to refold in such a way as to favour the formation of native disulphide bonds. Disulphide rearrangement, the rate-limiting step during refolding, can be achieved by thiol/disulphide exchange initiated by free thiol groups present in the prochymosin polypeptide, GSH/GSSG or protein disulphide isomerase.

Hydrophobic charge induction chromatography: salt independent protein adsorption and facile elution with aqueous buffers

A new form of protein chromatography, hydrophobic charge induction, is described. Matrices prepared by attachment of weak acid and base ligands were uncharged at absorption pH. At low ligand densities, protein adsorption was typically promoted with lyotropic salts. At higher ligand densities, chymosin, chymotrypsinogen and lysozyme were adsorbed independently of ionic strength. A pH change released the electrostatic potential of the matrix and weakened hydrophobic interactions, inducing elution. Matrix hydrophobicity and titration range could be matched to protein requirements by ligand choice and density. Both adsorption and elution could be carried out within the pH 5-9 range.

Protein engineering loops in aspartic proteinases: site-directed mutagenesis, biochemical characterization and X-ray analysis of chymosin with a replaced loop from rhizopuspepsin

The loop exchange mutant chymosin 155-164 rhizopuspepsin was expressed in Trichoderma reesei and exported into the medium to yield a correctly folded and active product. The biochemical characterization and crystal structure determination at 2.5 A resolution confirm that the mutant enzyme adopts a native fold. However, the conformation of the mutated loop is unlike that in native rhizopuspepsin and involves the chelation of a water molecule in the loop. Kinetic analysis using two synthetic peptide substrates (six and 15 residues long) and the natural substrate, milk, revealed a reduction in the activity of the mutant enzyme with respect to the native when acting on both the long peptide substrate and milk. This may be a consequence of the different charge distribution of the mutated loop, its increased size and/or its different conformation.

The primary structure and enzymic properties of porcine prochymosin and chymosin

Preliminary investigations by N-terminal sequence analysis showed that pig and calf chymosin possessed 80% amino acid sequence identity but showed considerable differences in their enzymatic properties. A comparison of their structures may therefore contribute to an understanding of the significance of the amino acid residues responsible for the differences in these properties. Pig chymosis was extracted from the stomachs of pigs of less than 3 weeks of age, and was purified by ion exchange chromatography. Half of the primary structure was determined by amino acid sequencing and the complete structure was deduced from a cloned chymosin cDNA. Results showed that the zymogen showed 81% sequence identity with calf prochymosin and 57% identity with pig pepsinogen A. The size of the propart and location of the residue which becomes the N-terminus in the active molecule were the same in the prochymosins. The maximum general proteolytic activity at pH 3.5 of pig chymosin was 2-3% of that of the activity of pig pepsin A at pH 2, whereas the milk clotting activity relative to the general proteolytic activity of pig chymosin was much higher than that of calf chymosin. Agar gel electrophoresis at pH 5.3 of stomach extracts of individual pigs showed the existence of two predominant genetic variants of zymogen and enzyme. The two variants could not be distinguished by amino acid composition or N-terminal sequencing, and no differences in the enzymatic properties of the genetic variants were observed. It was concluded that of the residues that participate in the substrate binding, calf and pig chymosin differ in the following positions (pig pepsin numbering, subsites in parentheses): Ser 12 Thr (S4), Leu 30 Val (S1/S3), His 74 Gln (S'2), Val 111 Ile (S1/S3), Lys 220 Met (S4). With regard to the low general proteolytic activity of pig chymosin, the substitution Asp 303 Val relative to calf chymosin may contribute to an explanation of this.

Buffalo (Bos buffali L.) chymosin purification and properties

Buffalo chymosin was isolated from abomasum mucosa extract of buffalo calves by affinity chromatography on gramicidin S-agarose followed by ion exchange chromatography on gamma-aminopropylsilochrom. Its molecular weight, 36 +/- 1 kDa, is similar to that of bovine calf chymosin. The N-terminal sequence Gly-Glu-Val-Ala-Ser-Val-Pro- coincides with that of bovine enzyme, whereas some differences were found in the amino acid composition of these enzymes. Buffalo and bovine enzyme possess similar but not identical structures. General proteolytic and milk-clotting activities of buffalo chymosin are also similar to those of bovine proteinase. pH-Optimum of its activity against hemoglobin lies at pH 4.0, somewhat higher than that for bovine chymosin, which indicates subtle differences in the functional properties of two enzymes.

Solid-phase synthesis of a peptide-ligand affinity matrix for isolation of chymosin

Aminopropyl Perloza beaded cellulose was used as the support for solid-phase synthesis of resin-bound Val-dLeu-Pro-Phe-Phe-Val-dLeu, an inhibitor of aspartic proteases. Both Boc and Fmoc SPPS methodologies were employed in separate syntheses. The peptide-resins were characterized by amino acid analysis. The peptide-resin from the Fmoc synthesis gave the better amino acid analysis of the two syntheses and was used for further studies. Following modification of the peptide N-terminus by succinylation, the peptide-resin was able to bind chymosin (E.C. 3.5.21.4). The peptide resin was used for isolation of chymosin from a crude recombinant broth.

Improved procedure for a high-yield recovery of enzymatically active recombinant calf chymosin from Escherichia coli inclusion bodies

The high-yield recovery of enzymatically active recombinant calf chymosin from Escherichia coli inclusion bodies was achieved by optimization of solubilization and renaturation conditions. The solubilization was carried out in 8 M urea at various pHs, at various temperatures, and for various periods of time. The following values were found optimal: 1 h at 31 degrees C, pH 10.4. For successful correct refolding of solubilized prochymosin molecules it was found to be necessary to dilute the solution into an alkaline buffer (pH 10.7) in such a way that the final concentration of urea did not exceed 0.32 M and that of protein 0.275 mg/ml. Our optimized procedure gives about eight times higher yields of enzymatically active chymosin than the current published methods.

Release and recovery of porcine pepsin and bovine chymosin from reverse micelles: a new technique based on isopropyl alcohol addition

After complete solubilization by the direct method, porcine pepsin was not released from AOT in isooctane reverse micelles even under aqueous-phase conditions which would not ordinarily allow uptake. Similarly, bovine chymosin, once forward-transferred at a pH below its isoelectric point, was not back-transferred into an aqueous contact phase buffered at a pH value above its isoelectric point. These results show that there is significant hysteresis in the forward- and backward-transfer processes and further imply that kinetics, and not equilibrium, control uptake or release processes for these enzymes. The addition of 10-15% isopropyl alcohol to the aqueous phase increases the rate of protein release dramatically and allows for nearly complete back-transfer of porcine pepsin and 70% back-transfer of bovine chymosin. IPA addition does not destroy the functional integrity of the system since forward transfer of bovine chymosin still occurs at pH values below (but not above) the pI of the protein.

Prochymosin expression in Bacillus subtilis

Prochymosin (PC) sequence was cloned in Bacillus subtilis using two kinds of plasmid constructions. In plasmid pSM316 the cDNA was inserted to obtain the intracellular expression of the enzyme. The enzyme turned out to be expressed in an insoluble form which could be converted to native enzyme under proper denaturing and refolding conditions. The levels of intracellular expression of PC were further enhanced by modifying the 5' region of the gene in a way that a two-cistron expression system was created. For the PC secretion, the cDNA was fused to the subtilisin leader sequence and expressed under the control of the B. subtilis neutral protease promoter. A properly folded PC was secreted by the cells, although to low levels.

Alteration of catalytic properties of chymosin by site-directed mutagenesis

Artificial mutations of chymosin by recombinant DNA techniques were generated to analyze the structure--function relationship in this characteristic aspartic proteinase. In order to prepare the mutant enzymes in their active form, we established procedures for purification of correctly refolded prochymosin from inclusion bodies produced in Escherichia coli transformants and for its subsequent activation. Mutagenesis by linker insertion into cDNA produced several mutants with an altered ratio of milk clotting activity to proteolytic activity and a different extent of stability. In addition to these mutants, several mutants with a single amino acid exchange were also constructed by site-directed mutagenesis and kinetic parameters of these mutant enzymes were determined by using synthetic hexa- and octa-peptides as substrates. Exchange of Tyr75 on the flap of the enzyme to Phe caused a marked change of substrate specificity due to the change of kcat or Km, depending on the substrate used. Exchange of Val110 and Phe111 also caused a change of kinetic parameters, which indicates functional involvement of these hydrophobic residues in both the catalytic function and substrate binding. The mutant Lys220----Leu showed a marked shift of the optimum pH to the acidic side for hydrolysis of acid-denatured haemoglobin along with a distinct increase in kcat for the octa-peptide in a wide pH range.

Fragments of prochymosin produced in Escherichia coli form insoluble inclusion bodies

Bovine prochymosin produced in Escherichia coli has been used as a model system to investigate factors which may cause a recombinant protein to accumulate as insoluble inclusion bodies. A series of plasmids was constructed to investigate the effect of deletions within the prochymosin-coding sequence on protein inclusion body formation. The results demonstrated that as much as 70% of the prochymosin-coding sequence could be deleted with no significant reduction in the accumulation of insoluble protein. The smallest deletion product identified (11,000 molecular weight) retained only one cysteine, yet this product still accumulated as an insoluble product in E. coli.

Separation of chymosin and pepsin in calf rennet by dye-ligand affinity chromatography

When calf rennet containing approximately 15% pepsin was applied to a Cibacron Blue agarose column at pH 5.5 in a low salt medium, pepsin passed through unadsorbed while chymosin was bound to the gel in the column. After washing the column, the bound chymosin was eluted with 1.7 M NaCl or 50% (v/v) aqueous ethylene glycol. The salt eluate was analyzed and found to contain greater than 97% pure chymosin. The fraction that passed through unadsorbed was found to contain greater than 96% pure pepsin. Thus a complete separation of chymosin and pepsin was effected by this technique without having to destroy either enzyme. Both enzymes are highly negatively charged at pH 5.5 but the separation does not arise from anion exchange since the gel functions as a cation exchanger. The separation appears to result from a combination of hydrophobic and electrostatic interactions of chymosin with Blue agarose. It is suggested that the enhanced affinity of chymosin to the Blue gel over pepsin may arise from topographically specified interaction between chymosin and the blue chromophore. Differential surface hydrophobicity may also play a key role, since in the presence of 0.7 M Na2SO4 the same behavior as at low ionic strength is observed.

New support for the large-scale purification of proteins

We propose a new affinity sorbent, matrix-linked histidine, for the large-scale purification of proteins. A variety of proteins and certain peptides, each distinct from the other, were purified. Immunoglobulin G from human placenta was chosen for a detailed study concerning the effects of coupling, spacer-arm and other parameters. Multiple interactions such as charge-transfer and other ionic reactions have been suggested to be responsible for the interactions between proteins and ligand.

Affinity precipitation of proteins using bis-dyes

Based on the principle of affinity precipitation of nucleotide-dependent enzymes using bis-NAD (Mosbach), Lowe et al. have recently mentioned the possibility of synthesising bis-dyes for similar applications. In this paper we report preliminary results obtained using bis-dyes in the sulphonamide form got through carbodiimide condensation of the monomer and its aminohexyl derivative for affinity precipitation. The dimer exhibited considerable selectivity for lactate dehydrogenase (90% yield). Bovine serum albumin gave a lower yield of 50% and as expected chymosin could not be precipitated by the dimer.

Isolation of human, swine, and rat prepepsinogens and calf preprochymosin, and determination of the primary structures of their NH2-terminal signal sequences

The total RNAs were extracted from human, swine, rat, and calf gastric mucosae, and translated in vitro in the presence of radiolabeled amino acids using a wheat germ cell-free system. Upon sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis of the translation products, a protein band with a molecular weight of about 43,000 was obtained in each case as one of the major products. These products could be specifically immunoprecipitated with a corresponding anti-pepsinogen or anti-chymosin antiserum. Radiosequence analysis of these translation products purified by SDS-polyacrylamide gel electrophoresis showed that each of them is a precursor form, i.e., prepepsinogen or preprochymosin, having an amino-terminal extension peptide (signal sequence) comprising 15 (human and swine) or 16 (rat and calf) amino acid residues. The primary structures of these signal sequences were determined to be as follows: (Sequence: see text). These signal sequences share common characteristics with those of other pre-secretory proteins, i.e., the presence of positive charges in the NH2-terminal region, hydrophobic amino acid clusters in the interior part, and amino acids with short side chains at the site of cleavage by the signal peptidase.

Fractionation of the multiple forms of bovine gastric aspartic proteases by chromatofocusing

By extending the chromatofocusing technique to a very acidic pH range (down to pH 2.0) a method which, in a single-step procedure, allows separation of the three main aspartic proteases secreted by the bovine abomasal mucosa i.e., chymosin (EC 3.4.23.4), gastricsin (EC 3.4.23.3), and pepsin A (EC 3.4.23.1), has been developed. Starting materials for separation were crude commercial milk-clotting extracts or abomasal juices. A multistep procedure, using narrower pH gradients, enabled the fractionation of these proteases into their multiple forms. Chymosins A and B, which are known to differ only by a single amino acid substitution (Asp/Gly), were completely resolved. Their elution pHs, 3.75 and 3.80, respectively, though far from their "normal" pIs (around 4.7 in isoelectric focusing), demonstrate the resolving power of such a technique. Multiple forms of bovine pepsin A, which differ in their organic phosphate content (0-3 phosphate group(s) per molecule of enzyme) and whose pIs are lower than 2.5, were also separated using 15-20 mM glycine buffer, pH 2.0, as eluent. Although many attempts to get a linear gradient remained unsuccessful within this pH range, resolution appeared quite satisfactory, as judged from analytical isoelectric focusing patterns. In particular, the two subcomponents of bpA1, which presumably have a different site of post-translational phosphorylation, were resolved in this way.

A simple method for purification of chymase from rat tongue and rat peritoneal cells

Chymase was purified from rat tongue and rat peritoneal cells by a simple new method involving hydrophobic chromatography on octyl-Sepharose 4B and hydroxylapatite column chromatography. This procedure can be completed in 1 or 2 days and the recovery is 45-60% from rat tongue and 32-47% from rat peritoneal cells. The specific activity of the purified enzyme is higher than that of crystallized enzyme previously reported (Y. Sanada, N. Yasogawa, and N. Katunuma (1978) Biochem. Biophys. Res. Commun. 82, 108-113). This procedure should be particularly useful for purifying chymase on a large scale from tissues in which it is present in relatively low concentrations.

Isolation and partial characterization of prochymosin and chymosin from cat

Extracts of cat gastric mucosa contain a zymogen that after activation shows partial immunochemical identity with chymosin (EC 3.4.23.4) from calf. Cat prochymosin has been purified by column chromatography and gel filtration, and cat chymosin was obtained after acid activation of the zymogen. The enzyme showed the optimum of general proteolytic activity at pH 2.5. The amino acid compositions of cat prochymosin and chymosin were similar to those of the corresponding proteins from calf. The first 27 residues of both cat prochymosin and chymosin have been sequenced. Among these 54 positions only 13 differences have been observed between the proteins from cat and calf. The results support the hypothesis that the chymosins form a group of neonatal gastric proteases with high milk-clotting activity, but with such weak general proteolytic activity that postnatal uptake of IgG is not hindered.

Photo-oxidation of a histidyl residue of milk-clotting acid protease, Mucor rennin

Mucor rennin, a milk-clotting acid protease produced by a fungus Mucor pusillus, was inactivated by photo-oxidation mediated by methylene blue according to first order kinetics. The pH profile of the inactivation rate showed that a dissociating group with a pK value of 7.6 was involved in the inactivation. Addition of pepstatin A, an inhibitor specific for acid proteases, caused a marked alkaline shift of the pK value. One of two histidyl residues in the enzyme was destroyed by the photo-oxidation, with complete loss of the enzyme activity. Analysis of inhibitor binding activity and chemical modification with diazoacetyl-DL-norleucine suggested that the photo-oxidized enzyme still retained its original conformation. These results indicated that one histidyl residue in addition to the two essential carboxyl groups is involved in the catalytic function of Mucor rennin.

Purification of prorennin and production of its antibody

Prorennin, i.e. the zymogen of rennin, was extracted from fresh calf stomach and purified by ammonium sulfate precipitation, ion exchange chromatography and gel filtration. The purified prorennin was homogeneous as judged by SDS-polyacrylamide gel electrophoresis. A specific antibody to the purified prorennin was induced in rabbits. In a double diffusion test and on immunoelectrophoresis the antibody gave a single precipitin line when run against crude and pure zymogen preparations. In the double diffusion test, the antibody also reacted with a purified rennin but not with gastric proteases (pepsin and pepsinogen) or other proteases (trypsin and Mucor rennin). When the antibody was tested against prorennin and rennin in the double diffusion test, a spur was formed at the junction of the precipitin lines against prorennin and rennin. This result confirms that the two proteins share an antigenically common structure in their molecules and that the activation segment of prorennin contains at least one antigenic determinant.

Partial purification and characterization of a yeast extracellular acid protease

During screening of 143 yeasts for proteolytic milk coagulating activity, a strain belonging to the species Cryptococcus albidus var. aerius was found which produced extracellular protease in shake culture. An enzyme preparation was obtained from the cell-free broth by ammonium sulphate precipitation. It possessed an optimum pH for milk-clotting at 5.5 to 5.7 at 35 degrees C. Maximum stability occurred between pH 3.5 and 5.5. The optimum temperature for the enzyme was 45 degrees C. Activity of the enzyme was inhibited by copper+2, iron+2, and mercury+2 ions.

Binding of Streptomyces pepsin inhibitor (acetyl-pepstatin) with chymosin (Rennin)

Chymosin (Rennin) was effectively purified using an AH-Sepharose 4B column. Binding of Streptomyces pepsin inhibitor (acetul-pepstatin) with chymosin was studied spectroscopically. The binding caused ultraviolet difference and CD spectral changes suggesting microenvironmental changes around tryptophan and/or tyrosine residue(s) in chymosin. The fluorescence intensity of a hydrophobic probe, 2-p-toluidinylnaphthalene-6-sulfonate, increased in the presence of chymosin and was further amplified when Streptomyces pepsin inhibitor was added to the chymosin-2-p-toluidinylnaphthalene-6-sulfonate solution. The binding and dissociation-rate constants between chymosin and the inhibitor were determined using 2-p-toluidinylhnaphthalene-6-sulfonate as a probe. The binding constant was determined from the binding and dissociation-rate constants, to be 3.1 . 10(7) M-1 at 25 degrees C, pH 5.5.

Production and isolation of milk-clotting enzyme from Aspergillus versicolor

The production of a milk-clotting enzyme by Aspergillus versicolor in 19 different culture media was investigated. Considerable milk-clotting activity was achieved by supplying corn steep liquor with either glucose of maltose. Dephytinization of corn steep liquor had an adverse effect on the production of milk-clotting enzyme. The results indicated that complex organic compounds favoured the production of the enzyme. Precipitation with acetone or tannin was unsuitable, but ammonium sulphate and ethanol above certain concentration produced active fractions.

Preparative purification of the rat mast cell chymase: characterization and interaction with granule components

The rat mast cell granule chymotrypsinlike enzyme was purified to homogeneity from 1 M NaCl solubilized membrane and granule-rich fractions of concentrated rat peritoneal mast cells by a preparative technique utilizing chromatography on Dowex 1, filtration on Sephadex G-75, and affinity chromatography with D-tryptophan methyl ester. Acid disk gel electrophoresis of the purified chymase disclosed a single stained band with activity being eluted from a replicate sliced gel in the same region. SDS-polyacrylamide gel electrophoresis of purified protein gave a single stained band that did not change in position with reduction and alkylation. Mast cell chymase is thus a cationic protein of 25,000 mol wt composed of a single polypeptide chain. The apparent K(m) of the chymase for BTEE was 1.5 x 10(-3) M and the V(max) was 67.8 mumol/min per mg. The enzyme was inhibited by TPCK and not by TLCK. The chymase complexed with native macromolecular rat mast cell heparin in molar ratios of 12:1 and 16:1, and complete heparin uptake occurred at a 40:1 ratio of chymase to heparin. Chymase activity was partially masked by combination with heparin in the isolated granule or experimental chymase-heparin complex, and soluble purified chymase was inhibited by concentrations of 5-HT comparable to those present in mast cells. It is therefore possible that the active site of chymase in the mast cell granule is largely masked by the combined effects of macromolecular heparin and 5-HT.

Activation studies of the multiple forms of prochymosin (prorennin)

Activation of the four separate components of prochymosin (prorennin) at pH 5.0 demonstrated that each zymogen was the precursor to an electrophoretically distinct chymosin (rennin). When the increase in milk-clotting activity with time was analysed, the mechanism of activation of unfractionated prochymosin, individual prochymosin components, and a mixture of the prochymosin fractions at pH 5.0 was shown to follow essentially autocatalytic kinetics. The activation of prochymosin C was completed in 70 h, whereas the other three fractions each required more than 110 h for complete activation under the same conditions. Intact prochymosin, the mixture of four components and prochymosin C were activated at similar rates. Interaction of the individual fractions during activation is suggested to explain the increased rate of the activation for the mixture. Comparison of autocatalytic activation of unfractionated prochymosin purified chromatographically at pH 6.7 and 5.7 demonstrated an increased rate of reaction of the zymogen prepared at the lower pH value. The possibility that prochymosin became susceptible to activation during preparation at pH values slightly below 6.0, as a result of changes in the proportion of the components or a conformational change and exposure of the active site, is discussed.

[Biospecific chromatography of acid proteinases. The role of ionic and hydrophobic interactions]

Pepsin chromatography was studied on peptide ligand sorbents, differing in the length of the polypeptide chains, ionogenic groups and the nature of hydrophobic side groups. Pepsin sorption was found to be dependent of a specific interaction of the substrate analogs with the enzyme and ionic interactions with the matrix and ionogenic groups of the ligand. Non-specific hydrophobic interactions of the enzyme and the ligand have little effect on the sorption. Efficient methods for the isolation of pepsin and separation of the mixture of bovine chymosin and pepsin are described.

[Biospecific chromatography of chymosin]

Chromatography of commercial rennet was studied on biospecific sorbents obtained by means of coupling of activated Sepharose 4B with epsilon-aminocapronyl-D-phenylalanine methyl ester and amide, epsilon-aminocapronyl-L-phenylalanyl-D-phenylalanine methyl ester, gramicidin S and N-2,4-dinitrophenylhexamethylenediamine. A mixture of two similar on their specificity enzymes chymosin and bovine pepsin was isolated from rennet by the chromatography on these sorbents. The individual enzymes might be isolated by chromatography on immobilized ribonuclease at pH 3,0, or by means of electrofocusing in pH gradient 4-6. Coloured inhibitor of acid proteases, N-diazoacetyl-N'-2,4-dinitrophenyl-ethylenediamine (DDE) is found to inactivate chymosin at pH 5,6 in the presence of Cu2+,one residue of the inhibitor being attached to the enzyme molecule. Unlike pig pepsin, chymosin is not inhibited with DDE at pH 4,7 and at the enzyme:DDE:Cu2+ ratio being 1:40:40. a synthesis of peptide sorbents is described.