Alkaline phosphatase of chick kidney

The alkaline phosphatase prepared from kidneys of domestic chicks is a tetramer (Mr 270,000) consisting of identical subunits (Mr 68,000). The tetramer may be dissociated by detergent treatment to a dimer (Mr 150,000) with no loss of catalytic activity. The tetramer probably represents the in vivo state. The enzyme is stimulated by Mg2+ and inhibited noncompetitively by Zn2+ and levamisole. The stimulation and inhibition show similar pH dependencies. Evidence for an essential histidine is provided by sensitivity of the enzyme to diethyl pyrocarbonate. It is suggested that chick kidney and bone phosphatases could be expressed by different genes.