Partial characterization of two mouse liver alkaline phosphatases that require manganese for activity

Two manganese requiring isozymes of alkaline phosphatase from the liver of the house mouse (Mus musculus)were studied to determine their properties and location within the cell. 2. The two isozymes, referred to as Region I and Region III, were located in the cytosol from liver homogenates. 3. Optimum activity for Region I isozyme at 37 degrees C was obtained at pH 9.1 and a manganese concentration of 0.5 mM. 4. Optimum conditions for Region III isozyme were pH 7.4 and 5.0 mM manganese. 5. Both isozymes were stable at 56 degrees C; Region III isozyme was stable at 65 degrees C, but Region I isozyme was partially deactivated to 35% of its original activity. 6. Both isozymes were completely deactivated at 75 degrees C within 30 min. Region I isozyme was inhibited by 10 mM L-homoarginine (30% of original activity) and 2.5 mM L-phenylalanine (66% of original activity). 7. No inhibition occurred with Region III isozyme in the presence of either chemical.