Nucleotidase with XMP as the best in vitro substrate. Low catalytic efficiencies of YKL033W-A observed with XMP and other substrates suggest that these could be secondary activities for this protein, and its primary substrate is not yet identified. May possess pseudouridine 5'-phosphatase activity and together with dTTP/UTP pyrophosphatase YOR111W might constitute a pathway for the detoxification of pseudouridine 5'-triphosphate (Psi-UTP) and -monophosphate (Psi-UMP). H2O + XMP = phosphate + xanthosine H2O + psi-UMP = phosphate + pseudouridine kcat is 1.9 sec(-1) with XMP as substrate. Belongs to the HAD-like hydrolase superfamily.