Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.3.1 (alkaline phosphatase)
 47,916 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Analogs of phosphophoryn, a calcium-binding phosphorylated protein found in mineralized dentin, were synthesized by solid phase peptide synthesis. The dentin phosphophoryn appears to contain some sequence blocks of (Asp-PhosphoSer)n. As this sequence is difficult to synthesize, polymers of (alpha-L-Glu-L-Ser) were prepared. The 30-peptide, (alpha-L-Glu-L-Ser)15, was phosphorylated by reaction with orthophosphoric acid in the presence of trichloroacetonitrile in anhydrous dimethylsulfoxide. Calcium ion binding studies were carried out with both the 30-peptide and phosphorylated 30-peptide. The conformation of the original 30-peptide, (Glu-Ser)15, was examined, in the presence and absence of calcium ion, by circular dichroism measurements. Purified bovine phosphophoryn, previously studied by the same techniques, was partially dephosphorylated by alkaline phosphatase, and its calcium ion binding properties were determined. Dephosphorylation to 31% of the initial phosphorus content reduced the number of high affinity sites to approximately 30% of the initial value. However, the stoichiometry of binding indicated that both phosphate and carboxylate groups participate in the high affinity binding and that the binding constant was decreased only slightly. Partial phosphorylation of the 30-mer raised the calcium binding constant, Ka, from 2.1 x 10(2) to 3.3 x 10(3) M-1 and increased the amount of binding from an electrostatic equivalent number of sites to a stoichiometric equivalent number. Concomitant with binding, there was a transition from random coil to beta-like structure. These data suggest that the repetitive (Asp-PhosphoSer)n regions in phosphophoryn and the (Glu-PhosphoSer)n sequence of the synthetic polymer have special conformations which favor the unidentate binding of calcium to the carboxyl groups and phosphate groups. and which enhance the binding affinities of the carboxyl groups in such sequences in a cooperative fashion.
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PMID:Cooperativity in calcium ion binding to repetitive, carboxylate-serylphosphate polypeptides and the relationship of this property to dentin mineralization. 678 Apr 83

Serine racemase (SR) is responsible for the biosynthesis of D-serine (D-Ser), an endogenous co-agonist for the glycine (Gly)-binding site on N-methyl-D-aspartate (NMDA) receptors, from L-Ser in the brain. We have previously demonstrated high expression of SR by chondrocytes in cartilage. In this study, we attempted to elucidate the possible functional role of D-Ser in chondrogenesis. Expression of mRNA and corresponding protein was seen for SR in cultured rat costal chondrocytes, while the addition of L-Ser significantly increased intracellular and extracellular levels of D-Ser. In organotypic cultured mouse embryonic metatarsals isolated before vascularization, SR mRNA was highly localized in hypertrophic and calcified chondrocytes. Exposure to D-Ser not only suppressed several chondrocytic maturation markers, including alkaline phosphatase (ALP) activity, Ca2+ accumulation, nodule formation, and osteopontin expression, in rat chondrocytes, but also delayed chondral mineralization in mouse metatarsals. Either NMDA or Gly alone significantly increased Ca2+ accumulation in cultured chondrocytes, whereas D-Ser significantly prevented Ca2+ accumulation by Gly, but not by NMDA. Gly alone also significantly increased gene transactivation by the introduction of runt-related transcription factor-2 (Runx2) in COS7 cells transfected with NR1 and NR3A subunits, while D-Ser significantly prevented the increase by Gly without affecting the promoter activity of Runx2. In both cultured chondrocytes and metatarsals from NR1-null mice, significant decreases were seen in ALP activity and chondral mineralization, respectively. These results suggest that D-Ser may negatively regulate cellular differentiation through inhibiting NMDA receptors composed of NR1 and NR3A subunits in a manner related to Runx2 transcriptional activity in chondrocytes.
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PMID:Interference with cellular differentiation by D-serine through antagonism at N-methyl-D-aspartate receptors composed of NR1 and NR3A subunits in chondrocytes. 1945 50

We have shown the functional expression by chondrocytes of serine racemase (SR) which is responsible for the synthesis of D-serine (Ser) from L-Ser in cartilage. In this study, we evaluated the possible functional expression of SR by bone-forming osteoblasts and bone-resorbing osteoclasts. Expression of SR mRNA was seen in osteoblasts localized at the cancellous bone surface in neonatal rat tibial sections and in cultured rat calvarial osteoblasts endowed to release D-Ser into extracellular medium, but not in cultured osteoclasts differentiated from murine bone marrow progenitor cells. Sustained exposure to D-Ser failed to significantly affect alkaline phosphatase activity and Ca(2+) accumulation in cultured osteoblasts, but significantly inhibited differentiation and maturation in a concentration-dependent manner at a concentration range of 0.1-1 mM without affecting cellular survival in cultured osteoclasts. By contrast, L-Ser promoted osteoclastic differentiation in a manner sensitive to the inhibition by D-Ser. Matured osteoclasts expressed mRNA for the amino acid transporter B(0,+) (ATB(0,+) ) and the system alanine, serine, and cysteine amino acid transporter-2 (ASCT2), which are individually capable of similarly incorporating extracellular L- and D-Ser. Knockdown of these transporters by siRNA prevented both the promotion by L-Ser and the inhibition by D-Ser of osteoclastic differentiation in pre-osteoclastic RAW264.7 cells. These results suggest that D-Ser may play a pivotal role in osteoclastogenesis through a mechanism related to the incorporation mediated by both ATB(0,+) and ASCT2 of serine enantiomers in osteoclasts after the synthesis and subsequent release from adjacent osteoblasts.
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PMID:Osteoclastogenesis is negatively regulated by D-serine produced by osteoblasts. 2225 36