Substrate specificities of base-level and induced forms of oncofetal alkaline phosphatase in HeLa cells.

HeLa65 cells contain an oncofetal form of alkaline phosphatase that exhibits an increase in catalytic activity when cultures are grown in medium containing adrenal glucocorticoid hormones such as hydrocortisone or its analogue prednisolone. The increase in alkaline phosphatase specific activity in cells grown with hormone is apparently the result of a reduced phosphate content of the enzyme which alters the transition state of the enzyme-substrate complex with an increase in catlytic efficiency. Fourteen different substrates possessing aliphatic, aromatic and heterocyclic configurations were studied with respect to the initial velocities of hydrolysis catalyzed by the base-level and induced forms of the enzyme. The magnitude of increase in catalytic activity was not substantially influenced by the structure of the nonphosphoryl moiety of substrates.