7 results for Prescott, Mark

  • A pepstatin-insensitive aspartic proteinase from a thermophilic Bacillus sp.

    Toogood, H.S.; Prescott, Mark; Daniel, Roy M. (1995)

    Journal article
    University of Waikato

    Bacillus sp. strain Wp22.A1 produced a cell-associated aspartic proteinase which was purified to homogeneity using phenyl-Sepharose (hydrophobic and affinity chromatography) and Mono Q. The proteinase has a molecular mass of 45 kDa by SDS/PAGE and a pI of 3.8. It is insensitive to pepstatin, but is sensitive to the other aspartic proteinase-specific inhibitors diazoacetyl-DL-norleucine methyl ester (DAN) and 1,2-epoxy-3-(p-nitrophenoxy)propane. Inactivation by DAN was only partial, suggesting that it had non-specifically modified an aspartate residue at a site other than the active site. The enzyme was not inhibited by any of the serine or cysteine proteinase inhibitors tested. Maximum proteolytic activity was observed at pH 3.5. The proteinase had a higher activity with haemoglobin, but was more specific (Vmax./Km) for cytochrome c. Substrate inhibition was observed with both these substrates. The cleavage of oxidized insulin B chain tended to occur at sites where the P1 amino acid was bulky and non-polar, and the P1' amino acid was bulky and polar, such as its primary cleavage site of Val2-Asn3. The proteinase was stable in the pH range 2.5-5.5. Thermostability was increased in the presence of Ca2+, although to a lesser extent at higher temperatures. The thermostabilities at 60, 70, 80 and 90 degrees C were 45 h, 102, 21 and 3 min respectively in the presence of Ca2+.

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  • Characterisation of a thermostable pepstatin-insensitive acid proteinase from a Bacillus sp.

    Prescott, Mark; Peek, Keith; Daniel, Roy M. (1995)

    Journal article
    University of Waikato

    An acid proteinase, Wai 21a, produced by a thermophilic Bacillus species (strain Wai 21a) has been purified to homogeneity by cation-exchange chromatography, phenyl-Sepharose chromatography and anion-exchange chromatography. A pI of 3.8 was determined by isoelectric focussing. The protein contained some associated carbohydrate (20 mol hexose equiv/mol proteinase). Optimal proteolytic activity was observed at pH 3.0 (at 60°C). The Leu¹⁵-Tyr¹⁶ bond was the major site of hydrolysis for the oxidized B chain of insulin. Enzyme activity was not affected by inhibitors of the cysteine, metallo or serine class of proteinases. The aspartate proteinase inhibitor, pepstatin, did not inhibit enzyme activity. Inhibition of enzyme activity by 1,2-epoxy-3-(p-nitrophenoxy)-propane indicated the presence of at least one carboxyl group essential to the catalytic mechanism of the enzyme. Proteinase activity was inhibited by diazoacetyl- -norleucine methyl ester in a slow and non-specific manner atypical of pepstatin-sensitive aspartate proteinases. Wai 21a proteinase may be classified as member of the pepstatin-insensitive group of aspartate proteinases. The thermal stability at pH 3.0 and 60°C increased 2.1-fold (t1/2, 4.5–9.7 hr) in the presence of 5 mM Ca⁺⁺. An increase in both pH (3.0–4.5) and Ca⁺⁺ concentration (0–30 mM) resulted in a 15-fold increase (t1/2, 15–230 min) in thermal stability at 75°C. The amino acid composition of Wai 21a proteinase was found to be similar to other pepstatin-insensitive proteinases from bacterial sources and in particular similar to the thermostable enzyme, kumamolysin.

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  • Some characteristics of a proteinase from a thermophilic Bacillus sp. expressed in Escherichia coli: comparison with the native enzyme and its processing in E. coli and in vitro.

    Peek, Keith; Veitch, Dallas P.; Prescott, Mark; Daniel, Roy M.; MacIver, Bryce; Bergquist, Peter L. (1993)

    Journal article
    University of Waikato

    Proteinase Ak.1 was produced during the stationary phase of Bacillus sp. Ak.1 cultures. It is a serine proteinase with a pI of 4.0, and the molecular mass was estimated to be 36.9 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The enzyme was stable at 60 and 70 degrees C, with half-lives of 13 h and 19 min at 80 and 90 degrees C, respectively. Maximum proteolytic activity was observed at pH 7.5 with azocasein as a substrate, and the enzyme also cleaved the endoproteinase substrate Suc-Ala-Ala-Pro-Phe-NH-Np (succinyl-alanyl-alanyl-prolyl-phenylalanine p-nitroanalide). Major cleavage sites of the insulin B chain were identified as Leu-15-Tyr-16, Gln-4-His-5, and Glu-13-Ala-14. The proteinase gene was cloned in Escherichia coli, and expression of the active enzyme was detected in the extracellular medium at 75 degrees C. The enzyme is expressed in E. coli as an inactive proproteinase at 37 degrees C and is converted to the mature enzyme by heating the cell-free media to 60 degrees C or above. The proproteinase was purified to homogeneity and had a pI of 4.3 and a molecular mass of 45 kDa. The NH2-terminal sequence was Ala-Ser-Asn-Asp-Gly-Val-Glu-, showing the exact signal peptide cleavage point. Heating the proenzyme resulted in the production of active proteinase with an NH2-terminal sequence identical to that of the native enzyme. The characteristics of the cloned proteinase were identical to those of the native enzyme.

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  • The use of phenyl-Sepharose for the affinity purification of proteinases

    Prescott, Mark; Peek, Keith; Veitch, Dallas P.; Daniel, Roy M. (1993)

    Journal article
    University of Waikato

    Phenyl-Sepharose is most often used as an adsorbent for hydrophobic interaction chromatography (HIC). We report on its effective use for the affinity purification of some extracellular thermostable proteinases from bacterial sources. Proteinases belonging to the serine, aspartate and metallo mechanistic classes were effective retained by the media. Purification factors in the range of 2.9–60 and enzyme activity yields in excess of 88% were obtained. In some cases homogeneous enzyme was obtained from culture supernatants in a single step. A number of other proteinases from mammalian sources were also retained. The specificity of the enzyme/support interaction was studied. Proteinases complexed with peptide inhibitors (pepstatin and chymostatin) showed reduced binding to phenyl Sepharose indicating with the active site cleft whereas modification with low molecular weight active site directed inactivators such as PMSF and DAN did not, indicating that binding may not be dependent on the catalytic site. Pepsinogen and the pro-enzyme form of the serine proteinase from the thermophilic Bacillus sp. strain Ak.1 were not retained by the media and could be resolved in an efficient manner from their active counterparts.

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  • Characterization of a chelator-resistant proteinase from Thermus strain Rt4A2

    Freeman, S.A.; Peek, Keith; Prescott, Mark; Daniel, Roy M. (1993)

    Journal article
    University of Waikato

    The Thermus isolate Rt4A2 was found to produce an extracellular chelator-resistant proteinase. The proteinase was purified to homogeneity by (NH4)2SO4 precipitation, cation-exchange chromatography, gel-filtration chromatography, and weak anion-exchange chromatography. The Rt4A2 proteinase was found to have properties typical of an alkaline serine proteinase. It had a pH optimum of 9.0 and was specifically inhibited by phenylmethanesulphonyl fluoride. Its isoelectric point was greater than 10.25. Its molecular-mass was 31.6 kDa as determined by SDS/PAGE. N-terminal sequencing has shown it to have high sequence similarity with other serine proteinases from Thermus species. The proteinase hydrolysed a number of substrates including fibrin, casein, haemoglobin, collagen, albumin and the synthetic chromogenic peptide substrate Suc-Ala-Ala-Pro-Phe-NH-Np. The specific activity of the purified proteinase using azocasein as substrate was 313 units/mg. Substrate inhibition was observed above an azocasein concentration of 0.05% (w/v). Esterase activity was directed mainly towards those substrates containing the aliphatic or aromatic residues of alanine, glycine, tryptophan, tyrosine and phenylalanine. Thermostability half-lives of greater than 7 days at 70 degrees C, 43 h at 80 degrees C and 90 min at 90 degrees C were found in the presence of 5 mM CaCl2. At 90 degrees C increasing the CaCl2 concentration 100-fold (0.5 mM to 50 mM) caused a 4.3-fold increase in the half-life of the enzyme from 30 to 130 min. Half-lives of 19.4 min at 100 degrees C and 4.4 min at 105 degrees C were found in the presence of 50 mM CaCl2. The metal chelators EGTA and EDTA reduced the stability at higher temperatures but had no effect on the activity of the proteinase. Activity was not stimulated by common metal activators such as Ca2+, Mg2+ and Zn2+.

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  • Purification and characterization of a pepstatin-insensitive, thermostable, extracellular acid proteinase from a bacterium

    Prescott, Mark; Peek, Keith; Prendergast, Elizabeth; Daniel, Roy M. (1992)

    Journal article
    University of Waikato

    Aspartate proteinases (also referred to as acid or carboxyl) represent one of the four major classes of proteinase. Work on members of this group has centered largely around those enzymes isolated from mammalian, fungal, or plant sources. Some of these have proven to be of great economic importance, for example, the renneting enzyme, chymosin.

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  • Some characteristics of a serine proteinase isolated from an extreme thermophile for use in kinetically controlled peptide bond synthesis

    Peek, Keith; Wilson, Shelley-Ann; Prescott, Mark; Daniel, Roy M. (1992)

    Journal article
    University of Waikato

    The use of proteinases for the synthesis of peptides and esters has been studied for over 50 years and has increased substantially over recent years. In particular, the use of proteinases in anhydrous organic solvents ( < 0.01% water), where they exhibit novel properties, is gaining momentum.¹ However, most of the work on peptide synthesis has been on the use of proteinases in water-miscible solvents. There are a number of advantages in employing water-miscible solvents.² For example, some amino acid derivatives are poorly soluble in nonpolar solvents and limitations due to the diffusion of substrates in biphasic systems or enzymes suspended in hydrophobic solvents are avoided. The main disadvantage of employing water-miscible solvents is that at high concentrations, many enzymes are relatively inactive or denatured due to the stripping of enzyme-bound water.³ The use of proteinases isolated from extreme thermophiles, with their inherent stability to extremes of pH and temperature and to organic solvents, would seem to be one of the obvious ways of solving these problems. In addition, the reactions could be carried out at higher temperatures, which would result in benefits from increased substrate solubilities, accelerated rates of diffusion, and decreased viscosity.

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