Some properties of the extracellular proteolytic enzymes of the milk-spoiling organism Pseudomonas aeruginosa ATCC 10145

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.

Purification and properties of a fibrinolytic enzyme from Bacillus subtilis

A fibrinolytic enzyme obtained from B. subtilis was purified, using DEAE-cellulose column chromatography, and gel filtration on Sephadex G-100. The preparation was homogeneous as tested by gel filtration on Sephadex G-200, and disc electrophoresis. The molecular weight of this enzyme was 29.400 estimated by gel filtration on Sephadex G-100. The optimum pH for enzyme activity was 7.2 Copper ions significantly increased enzyme activity, while Zn++ and Mn++ caused marked inhibition.

Some properties of two purified fibinolytic enzymes from Bacillus subtilis and B. polymyxa

Two fibrinolytic enzymes isolated from B. subtilis and from B. polymyxa were purified using a five step method. The pH optimum for the enzyme from B. subtilis was 7.2 and for the enzyme from B. polymyxa was 7.0. Both enzymes were activated by Cu++. The molecular weight of the first enzyme was 29,400 and that for the second enzyme was 18,000 on the basis of gel filtration on Sephadex G-100. The enzyme from B. subtilis has higher affinity to buffalo fibrin than towards human fibrin. The enzyme from B. polymyxa has higher affinity to human fibrin than towards buffalo fibrin.