Physicochemical Properties of Heat-Stable Proteases from Psychrotrophic Pseudomonads

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Abstract
Four purified heat-stable proteases from psychrotrophic pseudomonads were characterized and compared with other similar purified proteases. Amino acid compositions, hydrophobicities, Difference Index (DI) values, heat-stabilities, metal ion contents and N-terminal amino acids of these proteases were examined. Some similarities as well as differences in their amino acid compositions were observed. All were inactivated by EDTA-treatment and the apoenzymes were reactivated with either Ca, Mg or Mn ions. Proteases T25, T20, T16 and T13 contained 16, 8, 4 and 5 g atom per mol of Ca, respectively. Except for protease T20 which showed 4 g atom per mol of Mg, the other proteases showed less than 1 g atom per mol of the element. The Mn content of the proteases was negligible (less than 0.1 g atom per mol). The presence of exogenous Ca afforded protection to the protease activity in the partially purified enzymes when subjected to heat treatment. Heated samples of proteases when stored in cold regained activity indicating renaturation of the proteins. Threonine was tentatively identified as the N-terminal amino acid in the four purified proteases. Similarities and differences observed between purified proteases are discussed.