title: Novel phosphoserine phosphatase inhibitors.
abstract: Phosphoserine phosphatase (EC 3.1.1.3) catalyzes the final step in the major pathway of L-serine biosynthesis in brain. This enzyme may also regulate the levels of glycine and D-serine, the known and putative co-agonists for the glycine site of the N-methyl-D-aspartate receptor in caudal and rostral brain regions, respectively. Using L-phosphoserine as substrate, the rank order potency for inhibition of phosphoserine phosphatase was p-chloromercuriphenylsulfonic acid (CMPSA) > glycerophosphorylcholine >> hexadecylphosphocholine > or = phosphorylcholine > N-ethylmaleimide > or = L-serine > fluoride > D-2-amino-3-phosphonopropionic acid (D-AP3). Glycerylphosphorylcholine (IC50 18 microM) was found to be an uncompetitive inhibitor of phosphoserine phosphatase. Glycerylphosphorylcholine probably binds a novel site on the enzyme since the known allosteric inhibitor L-serine is highly selective for its feedback regulatory site, indicated by the inactivity of 25 L-serine analogs. Fluoride ion (IC50 770 microM) may bind the active site as has been shown for other Mg2+-dependent enzymes. The sulfhydryl reagent CMPSA is a potent, noncompetitive inhibitor of the enzyme using L-phosphoserine as substrate (IC50 9 microM) but is > 300-fold less potent using D-phosphoserine as substrate. Substrate-dependent differences are also observed with the sulfhydryl alkylator N-ethylmaleimide, which inhibits L-phosphoserine, but stimulates D-phosphoserine hydrolysis. These sulfhydryl reagents may dissociate multimeric forms of the enzyme to form monomers; the multimeric forms and monomers may preferentially cleave L- and D-phosphoserine, respectively. Phosphorylcholine esters and sulfhydryl reagents may prove useful in determining the contribution of phosphoserine phosphatase to the biosynthesis of glycine and D-serine in neuronal tissue in vitro.
authors.affiliation: CoCensys, Inc., Irvine, CA 92618, USA.
authors.forename: J E
authors.initials: JE
authors.lastname: Hawkinson
authors.forename: M
authors.initials: M
authors.lastname: Acosta-Burruel
authors.forename: N D
authors.initials: ND
authors.lastname: Ta
authors.forename: P L
authors.initials: PL
authors.lastname: Wood
mesh_terms: D000818:Animals; D001921:Brain / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005997:Glycerylphosphorylcholine / Q000494:pharmacology; D066298:In Vitro Techniques; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors*; D010768:Phosphoserine / Q000378:metabolism; D051381:Rats; D013237:Stereoisomerism; D013379:Substrate Specificity; D013439:Sulfhydryl Reagents / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D013439:Sulfhydryl Reagents; D010768:Phosphoserine; D005997:Glycerylphosphorylcholine; D010744:Phosphoric Monoester Hydrolases; C022394:phosphoserine phosphatase