The catalytic properties of alkaline phosphatases under various conditions

Abstract

A comparative study was performed to examine the catalytic properties of alkaline phosphatases from bacteria Escherichia coli and bovine and chicken intestines. The activity of enzyme dimers and tetramers was determined. The activity of the dimer was three or four times higher than that of the tetramer. The maximum activity and affinity for 4-nitrophenylphosphate was observed for the bacterial alkaline phosphatase (K _M = 1.7 × 10⁻⁵ M, V _max = 1800 μmol/(min mg of protein) for dimers and V _max = 420 μmol/(min mg of protein) for tetramers). The Michaelis constants were equal for two animal phosphatases in various buffer media (pH 8.5) ((3.5 ± 0.2) × 10⁻⁴ M). Five buffer systems were investigated: tris, carbonate, hepes, borate, and glycine buffers, and the lowest catalytic activity of alkaline phosphatases at equal pH was observed in the borate buffer (for enzyme from bovine intestine, V _max = 80 μmol/(min mg of protein)). Cu²⁺ cations formed a complex with tris-(oxymethyl)-aminomethane (tris-HCl buffer) and inhibited the intestine alkaline phosphatases by a noncompetitive mechanism.