Partial Purification and Characterization of Vitamin B6-P Phosphatases from Human Erythrocytes

Evolutionary and Structural Analyses of Mammalian Haloacid Dehalogenase-type Phosphatases AUM and Chronophin Provide Insight into the Basis of Their Different Substrate Specificities

“…Fig. 3A shows that AUM dephosphorylates pNPP, whereas the activity of chronophin measured in parallel was very low, as reported earlier (8,19,20). The replacement of the putative nucleophilic Asp in AUM with Asn (AUM D34N ) abolishes pNPP dephosphorylation, demonstrating that AUM is indeed an aspartate-dependent phosphatase.…”

“…To address these questions, we have analyzed AUM (aspartate-based, ubiquitous, Mg 2ϩ -dependent phosphatase; gene annotation,: phosphoglycolate phosphatase, PGP). This gene is the closest paralog of chronophin (also known as pyridoxal 5Ј-phosphate phosphatase) (8,19,20). Interestingly, AUM acts as a tyrosine phosphatase, whereas chronophin dephosphorylates serine/threonine-phosphorylated proteins (8,(21)(22)(23)(24) and PLP (19,20,25).…”

“…This gene is the closest paralog of chronophin (also known as pyridoxal 5Ј-phosphate phosphatase) (8,19,20). Interestingly, AUM acts as a tyrosine phosphatase, whereas chronophin dephosphorylates serine/threonine-phosphorylated proteins (8,(21)(22)(23)(24) and PLP (19,20,25). We have integrated evolutionary, biochemical, and structural analyses of AUM and chronophin to unravel the determinants behind the substrate specificity of these two closely related proteins.…”

Functional Diversity of Haloacid Dehalogenase Superfamily Phosphatases from Saccharomyces cerevisiae

“…The human PLP phosphatase PDXP (CIN) has been shown to also be active as a Ser(P)-specific protein phosphatase that directly dephosphorylates cofilin, a key regulator of actin polymerization that is present in all eukaryotes (38,113,114). The activity of human cofilin is regulated by phosphorylation (inactivation) at the conserved Ser-3 by specific kinases and dephosphorylation (activation) by the unrelated phosphatases CIN and SSH (38,115,116).…”

Vitamin B-6 Metabolism and Interactions with TNAP

“…These locations differed from the usual sites of both acid and alkaline phosphatase activity. In 1992 Fonda (1992) observed that human erythrocytes contained alkaline phosphatase activity associated with the stroma and a soluble acid phosphatase which hydrolyzed vitamin B-6 phosphates. The optimal pH was 6.5.…”