Stabilization of a psychrotrophic Pseudomonas protease by calcium against thermal inactivation in milk at ultrahigh temperature

The Potential of an Inexpensive Plant-Based Medium for Halal and Vegetarian Starter Culture Preparation

The restrictions for halal and vegetarian fermented products apply not only to the food ingredients, but also to the inoculum media. The utilization of a medium for lactic acid bacteria (LAB) leads to some issues from animal-derived proteins sources that may be doubtful for halal and/or vegetarian use. This study aimed to develop a plant-based medium for culturing and maintaining LAB. The result demonstrated that 10 g/L soybean powder in sweet potato extract was suitable for cultivating Lactiplantibacillus plantarum TISTR 2075 with no significant difference (p < 0.05) from MRS (de Man, Rogosa and Sharpe) in the cell number (9.12 log CFU/mL) and specific growth rate (0.04). The feasibility of a plant-based medium to grow and maintain the LAB strains from different origins was evaluated. Compared to MRS, Lpb. plantarum TISTR 2075, Lpb. plantarum MW3, and Lacticaseibacillus casei TISTR 1463 could grow almost as well in a plant-based medium. This medium was also suitable for maintaining the viability of LAB during storage, especially when subjected to slant agar stock culture. It is practical and costs at least 10 times less than MRS. Thus, this study created a low-cost plant-based medium that could be used in laboratories, especially for applications in halal and vegetarian food products.

The Impact of Low-Temperature Inactivation of Protease AprX from Pseudomonas on Its Proteolytic Capacity and Specificity: A Peptidomic Study

The destabilization of UHT milk during its shelf life can be promoted by the residual proteolytic activity attributed to the protease AprX from Pseudomonas. To better understand the hydrolysis patterns of AprX, and to evaluate the feasibility of using low-temperature inactivation (LTI) for AprX, the release of peptides through AprX activity on milk proteins was examined using an LC-MS/MS-based peptidomic analysis. Milk samples were either directly incubated to be hydrolyzed by AprX, or preheated under LTI conditions (60 °C for 15 min) and then incubated. Peptides and parent proteins (the proteins from which the peptides originated) were identified and quantified. The peptides were mapped and the cleavage frequency of amino acids in the P1/P1′ positions was analyzed, after which the influence of LTI and the potential bitterness of the formed peptides were determined. Our results showed that a total of 2488 peptides were identified from 48 parent proteins, with the most abundant peptides originating from κ-casein and β-casein. AprX may also non-specifically hydrolyze other proteins in milk. Except for decreasing the bitterness potential in skim UHT milk, LTI did not significantly reduce the AprX-induced hydrolysis of milk proteins. Therefore, the inactivation of AprX by LTI may not be feasible in UHT milk production.

Inhibition Enzyme-Linked Immunosorbent Assay for Detection of Pseudomonas fluorescens Proteases in Ultrahigh-Temperature-Treated Milk

An inhibition enzyme-linked immunosorbent assay was developed to detect low levels of the proteases extracted from four strains of Pseudomonas fluorescens. The assay detected between 0.24 and 7.8 ng of protease per ml of ultrahigh-temperature-treated milk and could be completed within 6 h. It could be used as a framework for a test system for quantifying spoilage proteases in dairy products.

Laboratory simulations of a commercial UHT treatment using an oil bath and a programmable, electronically temperature-controlled oven

Heat stability of secreted bacterial proteinase is normally assessed using an oil bath test in which the sample is heated at a temperature and time representing the commercial UHT treatment of milk. The temperature/time (T/t) profiles of the oil bath and the commercial UHT process being represented are not taken into account. Two laboratory procedures were used to simulate a commercial UHT process in which milk was heated to 140°C and held for 3 s in a Spiroflo heat exchanger. They consisted of a conventional oil bath test and the use of a programmable, electronically temperature-controlled oven.T/tprofiles were established for each heat treatment. TheT/tprofile of the oil bath test was predicted accurately using the governing heat transfer equation.B*andC*values, which measure the severity of a heat process, were calculated from theT/tprofiles and used to compare the three different heat treatments.B*andC*values of 4·95 and 1·92 respectively were calculated for the Spiroflo heat exchanger. An oil bath test, in which the sample was immersed in a bath at 136°C for 73 s, gave approximately the sameB*andC*values as calculated for the Spiroflo heat exchanger.B*andC*values of 5·01 and 1·73 respectively were calculated for the oven procedure. The oven test gave the better laboratory simulation of the Spiroflo UHT treatment. Despite the slight difference in each of theB*andC*values between the oven and the Spiroflo, theT/tprofile of the oven test closely resembled that of the Spiroflo. TheT/tprofile of the oil bath was completely dissimilar. Although it was possible to use an oil bath test to replicate simultaneously both theB*andC*values of this particular UHT treatment, this would not be the case for other commercial processes.

Heat stable proteinase fromPseudomonas fluorescensAH-70: purification by affinity chromatography on cyclopeptide antibiotics

A heat stable extracellular proteinase from the psychrotrophPseudomonas fluorescensAH-70 was purified to electrophoretic homogeneity by affinity chromatography on a gramicidin S–Sepharose-4B column. Bacitracin linked to Sepharose-4B was unable to retain any proteolytic activity, whereas the same antibiotic bound to AH-Sepharose-4B retained ~ 25% of the total activity. The purification procedure on the gramicidin S–Sepharose-4B column was easy to perform, fast and reproducible; it resulted in a 207-fold increase in the specific activity and a yield of 41% of the original activity. The purified enzyme was a monomer with a mol. wt of 33000. The enzyme hydrolysed whole casein and its fractions whereas no activity was observed against bovine serum albumin. The enzyme was a metalloproteinase. It was heat stable, havingD-values at 121, 135 and 150 °C of 3·8, 1·9 and 0·6 min respectively.

Studies on the thermostability of lactase (Streptococcus thermophilus) in milk and sweet whey

The stability of lactase fromStreptococcus thermophilusat 55 °C increased 7-fold, 2-fold and 1·5-fold in the presence of lactose, galactose and glucose respectively; maltose had no effect. Total stability over an 8 h period was more than 10-fold better in milk and sweet whey than in lactose solution, owing to the stabilizing influence of the milk proteins and the milk salts. Ovalbumin and reduced glutathione provided some extra stability but were not as effective as the milk components. In the absence of lactose the enzyme was less stable in milk and was not protected at all by sweet whey constituents. None of the milk protein fractions was as effective in the absence of lactose as when it was present. Enhanced thermostability of the enzyme in milk and sweet whey is due to contributions by all major milk components, but binding of lactose to the enzyme is the major factor controlling the extent of stabilization by other components.

Skim milk enhances the preservation of thawed -80 degrees C bacterial stocks

The results from bacterial strain recovery efforts following hurricanes Katrina and Rita are reported. Over 90% of strains frozen in 10% skim milk were recovered whereas various recovery rates were observed for glycerol-stored stocks (56% and 94% of Escherichia coli, depending upon the laboratory). These observations led to a viability comparison of Streptococcus pyogenes, Campylobacter jejuni, Borrelia burgdorferi, Salmonella enterica subsp. Typhimurium, Pseudomonas aeruginosa and E. coli strains stored in glycerol or skim milk. In all bacteria examined, 10% skim milk resulted in significantly longer viability after thawing than 15% glycerol solutions currently used in most laboratories.

An Extracellular Protease of Pseudomonas fluorescens Inactivates Antibiotics of Pantoea agglomerans

ABSTRACT Pseudomonas fluorescens A506 and Pantoea agglomerans strains Eh252 and C9-1 are biological control agents that suppress fire blight, an important disease of pear and apple caused by the bacterium Erwinia amylovora. Pseudomonas fluorescens strain A506 suppresses disease largely through competitive exclusion of E. amylovora on surfaces of blossoms, the primary infection court, whereas Pantoea agglomerans strains Eh252 and C9-1 produce antibiotics that are toxic to E. amylovora. In this study, an extracellular protease produced by A506 is characterized and evaluated for its capacity to inactivate the antibiotics produced by the strains of Pantoea agglomerans. Activity of the extracellular protease was optimal at pH 9 and inhibited by zinc- or calcium-chelators, indicating that the protease is an alkaline metalloprotease. In an agar plate bioassay, partially purified extracellular protease inactivated the antibiotics mccEh252 and herbicolin O, which are produced by Pantoea agglomerans strains Eh252 and C9-1, respectively. Derivatives of A506 deficient in extracellular protease production were obtained by transposon mutagenesis, and the aprX gene encoding the protease was cloned and sequenced. Strain A506 inactivated mccEh252 and herbicolin O in agar plate bioassays, whereas the aprX mutant did not inactivate the antibiotics. Both A506 and the aprX mutant were insensitive to antibiosis by C9-1 and Eh252; thus, the protease was not required to protect A506 from antibiosis. These data highlight a previously unknown role of the extracellular protease produced by Pseudomonas fluorescens A506 in interactions among plant-associated microbes.

Low molecular weight milk whey components protect Salmonella senftenberg 775W against heat by a mechanism involving divalent cations

AIMS

To investigate which components of milk increase the heat resistance of Salmonella senftenberg 775W, and to explore the mechanisms that could be involved in this protective effect.

METHODS AND RESULTS

The heat resistance of Salm. senftenberg was determined in a specially designed resistometer in several heating media. The molecules responsible for the thermal protective effect of milk were in the protein fraction, even in the < 3000 Da ultrafiltrate. The protective effect was lost when whey was demineralized. The former protective effect was restored when calcium or magnesium was added. Milk components protected cell envelopes of Salm. senftenberg from heat damage.

CONCLUSIONS

The protein fraction and divalent cations were responsible for the protective effect of milk. The whole protective effect on Salm. senftenberg was not the result of the addition of the protective effect of each component, but the result of a synergistic effect of some of them interacting.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work could be useful for improving food preservation and hygiene treatments. It also contributes to our knowledge of microbial physiology.

Kinetics of thermal inactivation of the extracellular proteinase from Pseudomonas fluorescens 22F: influence of pH, calcium, and protein

The influence of pH, calcium ion activity, protein, and enzyme purification on the kinetics of heat inactivation of the extracellular proteinase from Pseudomonas fluorescens 22F was studied in the temperature range 80-120 degrees C. At pH 5.5-8.6 the rate of inactivation increased slightly with increasing pH values. The pH dependence of inactivation suggests that the inactivation mechanism is mainly through deamidation. Calcium ion activity had no influence on the kinetics of heat inactivation of the proteinase. Addition of 1.8% sodium caseinate to the enzyme solution slightly decreased the heat stability of the proteinase, possibly because part of the inactivation of the proteinase is caused by aggregation to casein. Purification of the proteinase did not change the rate of thermal inactivation.

Purification and characterization of a metalloprotease from Chryseobacterium indologenes Ix9a and determination of the amino acid specificity with electrospray mass spectrometry

The heat-stable protease from Chryseobacterium indologenes Ix9a was purified to homogeneity using immobilized metal affinity chromatography. The enzyme was characterized as a metalloprotease with an approximate relative molecular mass of 24,000, a pH optimum of 6.5, and a high temperature optimum (50 degrees C). The metal chelator EDTA and the Zn2+-specific chelator 1,10-phenanthroline were identified as inhibitors and atomic absorption analysis showed that the enzyme contained Ca2+ and Zn2+. The activity of the apoenzyme could be restored with Ca2+, Zn2+, Mg2+, and Co2+. Phosphoramidon and Gly-d-Phe did not inhibit Chryseobacterium indologenes Ix9a protease. Heat inactivation did not follow first order kinetics, but showed biphasic inactivation curves. The protease has a Km of 0.813 microg. ml-1 for casein as substrate. Amino acid analysis showed that the protease contains a high amount of small amino acids like glycine, alanine, and serine, but a low concentration of methionine and no cysteine at all. Electrospray mass spectrometry of proteolysis fragments formed when insulin B chain was hydrolyzed showed cleavage at the amino terminal of leucine, tyrosine, and phenylalanine. A hydrophobic amino acid at the carboxyl donating side seems to increase the rate of reaction.

Biochemical and genetic characterization of an extracellular protease from Pseudomonas fluorescens CY091

Pseudomonas fluorescens CY091 cultures produce an extracellular protease with an estimated molecular mass of 50 kDa. Production of this enzyme (designated AprX) was observed in media containing CaCl2 or SrCl2 but not in media containing ZnCl2, MgCl2, or MnCl2. The requirement of Ca2+ (or Sr2+) for enzyme production was concentration dependent, and the optimal concentration for production was determined to be 0.35 mM. Following ammonium sulfate precipitation and ion-exchange chromatography, the AprX in the culture supernatant was purified to near electrophoretic homogeneity. Over 20% of the enzyme activity was retained in the AprX sample which had been heated in boiling water for 10 min, indicating that the enzyme is highly resistant to heat inactivation. The enzyme activity was almost completely inhibited in the presence of 1 mM 1,10-phenanthroline, but only 30% of the activity was inhibited in the presence of 1 mM EGTA. The gene encoding AprX was cloned from the genome of P. fluorescens CY091 by isolating cosmid clones capable of restoring the protease production in a nonproteolytic mutant of strain CY091. The genomic region of strain CY091 containing the aprX gene was located within a 7.3-kb DNA fragment. Analysis of the complete nucleotide sequence of this 7.3-kb fragment revealed the presence of a cluster of genes required for the production of extracellular AprX in P. fluorescens and Escherichia coli. The AprX protein showed 50 to 60% identity in amino acid sequence to the related proteases produced by Pseudomonas aeruginosa and Erwinia chrysanthemi. Two conserved sequence domains possibly associated with Ca2+ and Zn2+ binding were identified. Immediately adjacent to the aprX structural gene, a gene (inh) encoding a putative protease inhibitor and three genes (aprD, aprE, and aprF), possibly required for the transport of AprX, were also identified. The organization of the gene cluster involved in the synthesis and secretion of AprX in P. fluorescens CY091 appears to be somewhat different from that previously demonstrated in P. aeruginosa and E. chrysanthemi.

Thermal resistance of partially purified proteinase of Pseudomonas fluorescens P-26

Heat resistance of the Pseudomonas fluorescens P-26 proteinase in terms of D-value was studied in whole milk, skim milk, whey and 0.05 mol l-1 phosphate buffer at 72.5, 130, 135, 140, 145 and 150 degrees C subsequent to its partial purification through (NH4)2 SO4 precipitation (45-65% saturation) and solvent fractionation with 1.0 to 2.0 volumes of isopropanol. The D-value was maximum for the proteinase at all temperatures when determined in whole milk (D150 = 0.088).

Peptidases from two strains of Pseudomonas fluorescens: partial purification, properties and action on milk

Pseudomonas fluorescens strains 240 and 32A expressed cell-associated peptidase activity which was shown by subcellular fractionation to be primarily intracellular. Two peptidases were partly purified from strain 32A. One specifically hydrolysed N-alpha-benzoyl-DL-arginine-4-nitroanilide and was termed endopeptidase and the other hydrolysed L-lysine- and L-leucine-4-nitroanilide and was termed aminopeptidase. The endopeptidase had very low activity on bovine serum albumin compared with that of trypsin and probably was not a proteinase. The endopeptidase had a mol. wt of 33,000 and a pH optimum of 8.0. The enzyme was stimulated by Ca2+ and Mg2+ and inhibited by Co2+, Mn2+, Hg2+, Zn2+ and leupeptin. Soya bean trypsin inhibitor and phenylmethane sulphonyl fluoride (PMSF) had no effect on its activity. The aminopeptidase had a mol. wt of 44,000 and a pH optimum of 8.0. It was inhibited by all the metal ions mentioned above and by PMSF. Little proteolysis was found when ultra high temperature (UHT) sterilized milk was treated with cell-free extract from strain 32A. It was concluded that the cell-associated peptidases from Pseudomonas strains normally present in raw milk may not contribute significantly to the deterioration of UHT sterilized milk.

Purification and characterization of the extracellular proteinase of Pseudomonas fluorescens NCDO 2085

Pseudomonas fluorescens NCDO 2085 produced a single heat-stable extracellular proteinase in Na caseinate medium at 20 degrees C and pH 7.0. The proteinase was purified to electrophoretic homogeneity using chromatofocusing, gel filtration and ion-exchange chromatography. The purification procedure resulted in a 158-fold increase in the specific activity and a yield of 3.5% of the original activity. The enzyme is a metalloproteinase containing Zn and Ca, with an isoelectric point at 5.40 +/- 0.05 and a mol. wt of 40 200 +/- 2100. It is heat-stable having D-values at 74 and 140 degrees C of 1.6 and 1.0 min respectively; 40 and 70% of the original activity remained after HTST (74 degrees C/17 s) and ultra high temperature (140 degrees C/4 s) treatments respectively. The amino acid composition of the proteinase was determined and compared with those from other Pseudomonas spp.

Physicochemical properties of proteinases from selected psychrotrophic bacteria

The physicochemical properties of eight extracellular proteinases secreted by psychrotrophic bacteria of dairy origin have been studied. Seven of these proteinases were able to withstand ultra heat treatment (UHT) with D values at 140 degrees C ranging from 2 to 300 s. The six Pseudomonas fluorescens proteinases were glycoproteins of mol. wt 47000-49500. The two Serratia marcescens proteinases, of mol. wt of 51000, did not contain carbohydrate but in other respects were similar to the Pseudomonas proteinases. The proteinases were inhibited by various metal chelators and all contained Ca and Zn in similar proportions. Their amino acid compositions were similar, with alanine as the N-terminal group, cysteine completely absent and very low levels of methionine. Isoelectric points ranged from 5.10 to 8.25. Their physical and chemical properties enabled them to be classified as alkaline metalloendopeptidases. A similarity index (S delta n) was used to predict sequence homology between ten proteinases of known amino acid composition. Comparisons of S delta n of these proteinases showed only minor sequence differences except for those of Ps. fluorescens MC60. Heat resistance could not be related wholly to similarities in protein sequence, but could be related both to the strength of stabilizing Ca2+-protein interactions and to the randomness inherent within the folding of the peptide chain.

Purification and characterization of heat-stable proteases from Bacillus stearothermophilus RM-67

The extracellular proteases of Bacillus stearothermophilus RM-67 were purified by ammonium sulfate fractionation (40 to 70% saturation), gel filtration through Sephadex G-100, and diethylaminoethyl-Sephadex A-50 ion-exchange chromatography. Gel filtration resulted in separation of the enzyme preparation into one minor (protease I) and one major (protease II) peak. The three-step purification scheme resulted in 39.5-fold purification and an overall recovery of 8.1% of protease I and 87.8-fold purification and 59.7% recovery of protease II. Purified proteases had pH and temperature optima of 8.0 and 70 degrees C. Protease I and II, when together, retained 100% activity at 60 degrees C for 30 min. Manganese imported 100% stability to the pooled proteases at 65 degrees C for 30 min. Amino acid analysis of the major peak (protease II) revealed the absence of half cystine and methionine. Protease I and II had molecular weights of 67,610 and 19,950 and Michaelis-Menten constants (casein) of 1.33 and 2.0 mg/ml. Energy of activation was 14,300 cal/mol for protease I and 11,150 cal/mol for protease II. Corresponding heat of activation was l3,620 and 10,470 cal/mol.

Isolation and characterization of heat stable proteinases from Pseudomonas isolate AFT 21

Pseudomonas strain AFT 21 produced three heat stable extracellular proteinases in milk and nutrient broth at 7 or 21 degrees C, but the proportions depended on medium and cultivation temperature. The three proteinases were EDTA- and o-phenanthroline-sensitive metalloenzymes and were not inhibited by N-ethylmaleimide or phosphoramidon. Proteinases I and II showed maximum activity at pH 7-7.5 and proteinase III at pH 8.5. All three enzymes showed maximum activity at 45-47.5 degrees C, but had relatively high (19-27% of maximum) activity at 4 degrees C. They were unstable at 55 degrees C in phosphate buffer, pH 6.6, or synthetic milk ultrafiltrate (SMUF) containing 12 mmol Ca2+, but were stabilized by short preheating at 100 degrees C. They were extremely heat stable in both phosphate buffer and SMUF, pH 6.6, at 70-150 degrees C. Their D-values at 140 degrees C were 69, 54 and 80 s respectively. The Z-values for Pseudomonas AFT 21 proteinase III in phosphate buffer and SMUF were 29.7 and 30.3 degrees C respectively; the corresponding activation energies for inactivation were 8.7 x 10(4) J mol-1 and 9.2 X 10(4) J mol-1.

Inhibition by chelating agents of the formation of active extracellular proteinase by Pseudomonas fluorescens 32A

The effect of chelating agents on extracellular proteinase production by Pseudomonas fluorescens 32A was examined. Increasing concentrations of orthophosphate slightly stimulated growth while inhibiting proteinase synthesis. Fifty per cent inhibition was found at 35 and 28 mM-orthophosphate at 5 and 20 degrees C respectively. Extracellular protein concentration was reduced by 30% when cells were grown with 100 mM-orthophosphate. Polyacrylamide gel electrophoresis of the cell-free supernatants suggested that reduced enzyme synthesis had taken place as evidenced by the decrease in staining intensity of the protein band corresponding to the proteinase. Other phosphate compounds could replace orthophosphate as an inhibitor. Extent of inhibition was related to chain length; polyphosphates with 4-6 or 13-18 phosphorus atoms were the most effective inhibitors. EDTA (0.5 mM) completely inhibited proteinase synthesis. This inhibition could be partly reversed by Ca2+ and, to a lesser extent, Mn2+. Proteinase production at 5 degrees C in skim milk was completely inhibited by phosphate glass (P13-P18). Control experiments showed that loss of activity with chelators was not due to inhibition of preformed enzyme. The results suggest a possible role for polyphosphates in controlling proteinase production in stored milk.

Heat-stable protease from Pseudomonas fluorescens T16: purification by affinity column chromatography and characterization

A heat-stable extracellular protease from Pseudomonas fluorescens T16, a psychrotroph, was purified by affinity column chromatography on a carbobenzoxy-D-phenylalanine-triethylene tetramine-Sepharose-4B column. The purified enzyme is a monomer with a molecular weight of 38,905 +/- 2,000. In an analytical ultracentrifuge, the Schlieren profile revealed a single symmetrical peak. The sedimentation coefficient was estimated to be 3.93S. Alpha-casein was the preferred substrate, with a Km of 0.05 mM. Heating crude enzyme and purified enzyme in buffer at 50, 90, and 120 degrees C resulted in a rapid initial loss of more than 50% of the initial activity followed by a gradual inactivation which exhibited first-order kinetics. The activation energy for the hydrolysis of casein was calculated to be 3.2 kcal/mol (13.4 kJ/mol).

Heat-stable proteases from psychrotrophic pseudomonads: comparison of immunological properties

A heat-stable extracellular protease from Pseudomonas fluorescens was purified by chromatography on a DEAE-cellulose column and gel filtration on a Sephadex G100 column. The homogeneous enzyme preparation was used to prepare antiserum in rabbits. The rabbit antiserum was used to study the antigenic relatedness of proteases from 19 psychrotrophic pseudomonads isolated from raw milk. The inhibition of the proteases by the antiserum and the gel precipitin reactions revealed similar antigenic determinants in proteases from different isolates. Rabbit antiserum to the purified protease gave precipitin bands with antigens (proteases) from 10 different isolates. However, the same antiserum did not inhibit the protease activity in cell extracts of isolates T10, T13, and T24. By determining serological cross-reactions, proteases from psychrotrophic pseudomonads were shown to be different from one another.

Thermal stability of an extracellular proteinase from Pseudomonas fluorescens AFT 36

A metalloproteinase, isolated from a shaken milk culture of Pseudomonas fluorescens AFT 36 by chromatography in DEAE and CM-cellulose and Sephadex G-150, was very unstable in 0.1 M-phosphate buffer, pH 6.6, being completely denatured above 70 degrees C in 1 min. It was also unstable in a Ca-containing buffer (synthetic milk salts, SMS) between 50 and 60 degrees C (minimum at 55 degrees C), but stability was very high above 80 degrees C in this buffer. D-values were determined at 10 degrees C intervals in the range 70-150 degrees C in SMS from which a Z value of 31.9 degrees C and an Ea of 8.82 X 10(4) J mol-1 were calculated; the half-life at 150 degrees C was 9 s. Instability at 55 degrees C was due to autolysis as evidenced by gel electrophoresis, gel filtration and increase in 2,4,6-trinitrobenzenesulphonic acid-reactive amino groups. The extent of inactivation experienced at 80 degrees C was inversely related to the rate of heating to 80 degrees C, i.e. length of time spent in the neighbourhood of 55 degrees C. Addition of increasing concentrations of caseinate substrate reduced inactivation of the enzyme at 55 degrees C, presumably due to substrate binding. Attempts to stabilize the enzyme at 55 degrees C by addition of EDTA or by adjusting the reaction pH to 4.2, at which the enzyme has little proteolytic activity, were unsuccessful, although autolysis was prevented. Unlike the proteinase from Ps. fluorescens MC 60, AFT 36 proteinase did not inactivate itself on cooling to 55 degrees C from 80, 100 or 150 degrees C, but did regain autolytic activity on cooling to below 50 degrees C to an extent dependent on the duration of holding at the lower temperature. It is suggested that on heating to approximately 55 degrees C, a conformational change occurs which renders the enzyme susceptible to proteolysis by still active enzyme; at higher temperatures the enzyme, although susceptible to autolysis, is inactive; an active conformation is restored on cooling to below 50 degrees C.

Isolation and general characterization of a heat-stable proteinase from Pseudomonas fluorescens aft 36

An extracellular proteinase from Pseudomonas fluorescens, strain AFT 36, was isolated to homogeneity by chromatography on DEAE-cellulose and Sephadex G-150; a 230-fold increase in specific activity with a recovery of 53% was obtained. The enzyme was optimally active at pH 6.5 and 45 degrees C; activity declined rapidly at higher temperatures but significant activity persisted down to 4 degrees C. Activity was strongly inhibited by 10(-3) M EDTA and was partially restored by addition of Zn2+, Ca2+ or Co2+. The Km values on methylated casein and sodium caseinate were 18.2 and 7.1 mg/ml, respectively. The enzyme was very labile in phosphate buffer and in a mild salts buffer at 55 degrees C but was very stable in the latter at more than 80 degrees C.

Unique response to heat of extracellular protease of Pseudomonas fluorescens M5

Eight proteases selected from 38 cultures of psychrotrophic bacteria were subjected to heat stability tests. Cell-free filtrates of the broth in which the cultures were grown individually were heated to 40, 50, 60, and 70 degree C for 0, 15, 30, and 60 min. Six of the filtrates were less than 50% inactivated by heating at 40 degree C for 60 min, whereas the enzyme of Pseudomonas fluorescens M5 was inactivated completely by this treatment. Of the five most proteolytic cultures tested, including P. fluorescens M5, losses in protease activity ranged from 9 to 34% on heating at 70 degree C for 60 min. Purified M5 protease retained at least 75% of its activity over the pH range of 4.5 to 7.5. Electrophoresis of active M5 protease from four chromatographed fractions revealed two bands in each with approximate molecular weights of 35,000 and 45,000. Heating at 40 degree C did not alter mobility of either band. Reasons for lability at 40 degree C but stability at 50, 60, and 70 degree C are discussed. Complexation with casein, observed with another protease, was not a possible explanation for stability at 40 degree C.

Thermal inactivation of a heat-resistant lipase produced by the psychotrophic bacterium Pseudomonas fluorescens

Lipase from Pseudomonas fluorescens was studied for thermostability at temperatures ranging from 100 C to 160 C. The heat treatments were in two media, and heating times necessary to inactivate 90% of the enzyme at constant temperature were extremely long even at high temperatures, e.g. 3.6 min at 140 C in nutrient broth and 2.0 min at 170 C in skim milk. The increments of temperature to reduce these heating times 90% were 37.0 C in nutrient broth and 38.9 C in skim milk. The lipase was inactivated only partly after 20 h at 20 C in 8 M urea, 6 M guanidine hydrochloride, and 1.0% sodium dodecyl sulfate. Four percent 2-mercaptoethanol showed no effect.

Thermostability at ultrahigh temperatures of thermolysin and a protease from a psychrotrophic Pseudomonas

Thermal inactivation at 110-150 degrees C of thermolysin (EC 3.4.24.4), produced by the thermophile Bacillus thermoproteolyticus, and the extracellular protease of Pseudomonas sp. MC60 a psychotroph, were investigated at 130 degrees C, both enzymes had approximately the same deltaH (22 kcal/mol) and deltaS (-13.5 cal/mol per degree) values. Both enzymes contain zinc and calcium. The amino acid compositions of the enzymes were similar except that MC60 protease exhibited a more typical tyrosine content. Comparable heat resistance at extreme temperatures of enzyme produced by psychrotrophic and thermophilic organisms emphasizes the difference between molecular properties that resist denaturation at elevated temperatures and those that allow reversible denaturation.