Class B nonspecific acid phosphatase from Salmonella typhimurium LT2: Phosphotransferase activity, stability and thiol group reactivity

The class B acid phosphatase (AphA) from Salmonella typhimurium LT2 exhibits phosphotransferase activity in addition to its intrinsic phosphohydrolase activity. It was shown that the enzyme transfers phosphate groups from an organic phosphoric acid ester (donor) to the hydroxyl groups of various alcohols (acceptors). With aliphatic, primary alcohols phosphotransferase activity increased at the expense of phosphohydrolase activity with increasing number of carbon atoms of the acceptor. Secondary, tertiary and branched alcohols and those containing additional hydrophilic, polar, or charged groups were less efficient as acceptors. The ratio of phosphotransferase to phosphohydrolase activity is independent of donor concentration whereas it rises with increasing acceptor concentration. Detergents or polyethylene glycol were indispensible for enzyme stability. Nonionic detergents are able to reactivate surface inactivated enzyme. A single cystein group present in the polypeptide chain of the native, homotetrameric enzyme is able to form disulfid bridges between subunits without affecting enzyme activity.