Dictyostelium phenylalanine hydroxylase is activated by its substrate phenylalanine

► Domain structures were examined via truncated proteins. ► Dictyostelium PAH is functional and stable as a tetramer in vivo. ► Dictyostelium PAH is activated by phenylalanine. ► Regulatory domain functions differently from that in human PAH. We have studied the regulatory function of Dictyostelium discoideum Ax2 phenylalanine hydroxylase (dicPAH) via characterization of domain structures. Including the full-length protein, partial proteins truncated in regulatory, tetramerization, or both, were prepared from Escherichia coli as his-tag proteins and examined for oligomeric status and catalytic parameters for phenylalanine. The proteins were also expressed extrachromosomally in the dicPAH knockout strain to examine their in vivo compatibility. The results suggest that phenylalanine activates dicPAH, which is functional in vivo as a tetramer, although cooperativity was not observed. In addition, the results of kinetic study suggest that the regulatory domain of dicPAH may play a role different from that of the domain in mammalian PAH. dicPAH and dicPAHbind by molecular sieving (View Interaction: 1, 2, 3, 4)