Isolation and characterization of heat stable proteinases fromPseudomonasisolate AFT 21

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Abstract
Pseudomonas strain AFT 21 produced three heat stable extracellular proteinases in milk and nutrient broth at 7 or 21 °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 °C, but had relatively high (19–27% of maximum) activity at 4 °C. They were unstable at 55 °C in phosphate buffer, pH 6·6, or synthetic milk ultrafiltrate (SMUF) containing 12 mmol Ca2+, but were stabilized by short preheating at 100 °C. They were extremely heat stable in both phosphate buffer and SMUF, pH 6·6, at 70–150 °C. Their D-values at 140 °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 °C respectively; the corresponding activation energies for inactivation were 8·7 × 104 J mol-1 and 9·2 x 104 J mol-1.
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