Partial purification and characterization of an extracellular proteinase fromAeromonas hydrophilastrain A4

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Abstract
Summary: An extracellular metalloproteinase fromAeromonas hydrophilastrain A4, isolated from milk, was purified by a factor of 300 by chromatogrpahy on DEAE-cellulose and Sephadex G-150. The enzyme had a mol. wt of 43000 and contained 2 g atom Ca/mol. It was active over a pH range 4·8–9·5 and had optimum activity on casein at pH 7·0 withKm= 0·17 mM. It was strongly inactivated by metal chelators and the apoenzyme was fully reactivated with Ca2+, Mn2+or Co2+. Heavy metal ions such as Ag+, Hg2+, Fe2+, Zn2+, Cd2+, Ni2+and Cu2+totally or partly inactivated the enzymic activity at 5 mM concentration. The enzyme was not inactivated by diisopropylfluorophosphate, soyabean trypsin inhibitor or sulphydryl group reagents. It was optimally active at 45 °C; above 50 °C activity declined rapidly, but significant activity persisted at 4 °C. It was heat labile in phosphate or Tris-maleate buffer but exogenous Ca2+afforded protection.