The plasmodia of Physarum polycephalum grow as multinucleated cells in the presence of sufficient humidity and nutriment. Under non-illuminating conditions, stresses such as low temperature or high concentrations of
salts transform the plasmodia into spherules whereas
dehydration induces sclerotization. Some
phosphatases including
protein phosphatase and
acid phosphatase have been purified from the plasmodia, but
alkaline phosphatase remains to be elucidated.
Phosphatase of the plasmodia, spherules and sclerotia was visualized by electrophoresis gel-staining assay using
5-bromo-4-chloro-3-indolyl phosphate. Insoluble fractions of the sclerotia were abundant in
phosphatase activity. The
phosphatase which was extracted by nonionic
detergent was subjected to column chromatography and preparative electrophoresis. Purified
phosphatase showed the highest activity at pH 8.8, indicating that this
enzyme belongs to
alkaline phosphatase. The apparent molecular mass from
sodium dodecyl sulfate-
polyacrylamide gel electrophoresis under non-reducing condition was estimated to be 100 kDa whereas that under reducing was 105 kDa. An amount of 1%
sodium dodecyl sulfate or 0.5 M NaCl had no effects on the activity although the
phosphatase showed heat instability, Mg(2+)-dependency and sensitivity to 2-glycerophosphate or NaF. The extracting conditions and enzymatic properties suggest that this
alkaline phosphatase which is in a membrane-bound form plays important roles in
phosphate metabolism.