Factors Affecting the Activity and Stability of Alkaline Phosphatase in a Marine Pseudomonad

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RESUMO

Conditions optimum for the assay of alkaline phosphatase of marine pseudomonad B-16 (ATCC 19855) and for maintaining the activity of the enzyme have been determined. The pH for optimal activity of the cell-bound enzyme was 9.0, whereas that for the enzyme after its release from the cells exceeded 9.4. Release was effected by first washing the cells in 0.5 M NaCl and then suspending them in 0.5 M sucrose. In the absence of salts, the activity of the cell-bound enzyme decreased rapidly at 25 C and less rapidly at 4 C. This loss of activity could be arrested but not restored by adding Mg2+. In the presence of Na+, activity of the cell-bound enzyme dropped to about 50% of that prevailing initially, but in this case adding Mg2+ restored enzyme activity completely. The activity of the enzyme after its release from the cells into 0.5 M sucrose was approximately 50% of that of the equivalent amount of enzyme in the original cells. This activity was relatively stable at both 25 and 4 C. Adding Mg2+ to the released enzyme restored its activity to that of the cell-bound form. The synthesis of alkaline phosphatase by the cells was not affected by adding 50 mM inorganic phosphate to the growth medium. The Km of the released enzyme for p-nitrophenyl phosphate was found to be 6.1 × 10−5 M.

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