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

Ascorbic acid, isoascorbic acid and dehydroascorbic acid inhibit bovine kidney alkaline phosphatase activity. Ascorbic acid free radicals seem not to be involved. Dialysis does not make the inactivation reversible. A competitive mechanism can be inferred from experiments with phosphate and substrates, which block the activity decay. The influence of temperature, pH, other inhibitors and tertiary structure modifications on the inactivation process is also investigated.
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PMID:Characterization of alkaline phosphatase inactivation by ascorbic acid. 647 37

Ascorbic acid, isoascorbic acid and dehydroascorbic acid quench the tryptophyl fluorescence of alkaline phosphatase. The quenching is protein aspecific, although its extent reflects the different inhibitory efficiency of the compounds. The kinetic inactivation and emission deactivation of alkaline phosphatase isoenzymes present also striking similarities. The fluorescence modifications, moreover, show a particular pattern, indicative of a transition phenomenon. The quenching effects displayed by the ascorbic system on alkaline phosphatase can then supply an interesting insight into other aspects of the inhibitor-enzyme interaction.
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PMID:Modifications induced by ascorbic acid on alkaline phosphatase fluorescence. 651 5

Ascorbic acid is found strikingly to decrease the activity of bovine kidney alkaline phosphatase in vitro. The inhibition of alkaline phosphatase is a function of ascorbic acid concentration and is time and temperature dependent. The presence of the substrate protects the enzyme against the inhibitory action of the vitamin.
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PMID:Ascorbic acid and alkaline phosphatase activity. 661 28

The organ-specific modulation by ascorbic acid and related compounds on alkaline phosphatase activity of calf intestinal and human placental tissues has been studied at pH 8.0 and 37 degrees C. L(+)-ascorbic acid and its isomer D(-)-ascorbic acid inhibit to a similar extent the intestinal isoenzyme and appear to be more potent modifiers than dehydro-L-(+)-ascorbic acid. In contrast, the placental isoenzyme shows an initial activation by the three chemical agents, followed by an inhibition. The inhibition is lower with L(+)-ascorbic acid and D(-)-ascorbic acid, while its catalytic activity is affected only slightly by dehydro-L-(+)ascorbic acid.
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PMID:Modulation of alkaline phosphatase in different organs by ascorbic acid and related compounds. 667 74

Ascorbic acid is necessary for expression of the osteoblast phenotype. We examined whether Na(+)-dependent transport is required for MC3T3-E1 preosteoblast cells to respond to vitamin C and investigated the role of membrane transport in the intracellular accumulation and function of ascorbate. MC3T3-E1 cells were found to possess a saturable, stereoselective, Na(+)-dependent ascorbic acid transport activity that is sensitive to the transport inhibitors sulfinpyrazone, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, and phloretin. Transport activity showed no competition with glucose or 2-deoxyglucose and was not inhibited by cytochalasin B, indicating that it is distinct from known hexose transporters. On addition of 100 microM ascorbic acid to the extracellular medium, intracellular concentrations of 10 mM were reached within 5-10 h and remained constant for up to 24 h. A good correlation was observed between intracellular ascorbic acid concentration and rate of hydroxyproline synthesis. Although ascorbic acid was transported preferentially compared with D-isoascorbic acid, both isomers had equivalent activity in stimulating hydroxyproline formation once they entered cells. Marked stereoselectivity for extracellular L-ascorbic acid relative to D-isoascorbic acid was also seen when alkaline phosphatase and total hydroxyproline were measured after 6 days in culture. Moreover, ascorbic acid transport inhibitors that prevented intracellular accumulation of vitamin blocked the synthesis of hydroxyproline. Thus Na(+)-dependent ascorbic acid transport is required for MC3T3-E1 cells to achieve the millimolar intracellular vitamin C concentrations necessary for maximal prolyl hydroxylase activity and expression of the osteoblast phenotype.
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PMID:Requirement for Na(+)-dependent ascorbic acid transport in osteoblast function. 761 63

The regulation of synthesis and phosphorylation of osteopontin in relation to avian epiphyseal growth-plate chondrocyte differentiation was studied in situ and in culture. Osteopontin gene expression was evaluated in the tibia growth-plate of 3-week-old chickens by in situ hybridization. The gene was expressed mainly at the lower hypertrophic zone where cartilage matrix is calcified and endochondral bone formation is initiated. Within the hypertrophic region, a poorly labeled area separated the layer of osteopontin-positive hypertrophic chondrocytes from those associated with endochondral bone formation. In culture, proliferative chondrocytes show no alkaline phosphatase activity in contrast to ascorbic acid-treated chondrocytes which display the enzyme activity. Chondrocytes not treated with ascorbic acid, exhibited lower levels of osteopontin mRNA than the treated cells. The phorbol ester TPA--an activator of protein kinase C--and to a lesser extent FGF but not EGF, stimulated osteopontin gene expression. Chondrocytes secreted low levels of phosphorylated osteopontin to the medium. EGF treatment resulted in the appearance of phosphorylated osteopontin in the medium, without affecting the synthesis of other proteins. FGF and TGF beta, but not IGF-I or IGF-II, also caused phosphorylation of osteopontin. Ascorbic acid-treated chondrocytes secreted higher levels of phosphorylated osteopontin than the non-treated cells, but addition of FGF or TPA did not stimulate osteopontin phosphorylation any further. Parathyroid hormone caused a dose-dependent attenuation of osteopontin phosphorylation and inhibited the EGF-dependent osteopontin phosphorylation. The results suggest that osteopontin gene expression and phosphorylation in chondrocytes are regulated by separate mechanisms. The response to the various controlling agents varies with the state of differentiation. Both processes--the synthesis and phosphorylation of osteopontin--are under the control of local growth factors which are involved in bone growth and calcification.
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PMID:Synthesis and phosphorylation of osteopontin by avian epiphyseal growth-plate chondrocytes as affected by differentiation. 765 84

L-Ascorbic acid 2-phosphate (Asc-P: a stable ascorbic acid derivative) markedly stimulated synthesis of marker proteins for osteoblastic differentiation such as alkaline phosphatase and osteocalcin in a murine osteoblastic cell line, MC3T3-E1, suggesting that Asc-P could promote osteoblastic differentiation. L-Azetidine 2-carboxylate (AzC) diminished the stimulatory effects of Asc-P on the synthesis of alkaline phosphatase and osteocalcin due to its inhibitory effects on mature collagen secretion. Growing cells on the dishes coated with type I collagen resulted in an increased expression of osteoblastic phenotypes even in the presence of AzC. Coating with fibronectin, however, failed to promote differentiation. These results suggest that the promotion of cell differentiation caused by Asc-P is mediated by the accumulation of mature collagen.
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PMID:L-ascorbic acid 2-phosphate promotes osteoblastic differentiation of MC3T3-E1 mediated by accumulation of type I collagen. 796 12

Matrix vesicles, media vesicles, and plasma membranes from three well-characterized, osteoblast-like cells (ROS 17/2.8, MG-63, and MC-3T3-E1) were evaluated for their content of enzymes capable of processing the extracellular matrix. Matrix vesicles were enriched in alkaline phosphatase specific activity over the plasma membrane and contained fully active neutral, but not acid, metalloproteinases capable of digesting proteoglycans, potential inhibitors of matrix calcification. Matrix vesicle enrichment in neutral metalloproteinase varied with the cell line, whereas collagenase, lysozyme, hyaluronidase, and tissue inhibitor of metalloproteinases (TIMP) were not found in any of the membrane fractions examined. MC-3T3-E1 cells were cultured for 32 days in the presence of ascorbic acid (100 micrograms/ml), beta-glycerophosphate (5 mM), or a combination of the two, to assess changes in matrix vesicle enzymes during calcification. Ascorbate or beta-glycerophosphate alone had no effect, but in combination produced significant increases in both active and total neutral metalloproteinase in matrix vesicles and plasma membranes, with the change seen in matrix vesicles being the most dramatic. This correlated with an increase in the formation of von Kossa-positive nodules. The results of the present study indicate that osteoblast-like cells produce matrix vesicles enriched in proteoglycan-degrading metalloproteinases. In addition, the observation that matrix vesicles contain significantly increased metalloproteinases under conditions favorable for mineralization in vitro lends support to the hypothesis that matrix vesicles play an important role in extracellular matrix processing and calcification in bone.
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PMID:Matrix vesicles produced by osteoblast-like cells in culture become significantly enriched in proteoglycan-degrading metalloproteinases after addition of beta-glycerophosphate and ascorbic acid. 806 58

Treatment of mouse MC3T3-E1 cells with ascorbic acid initiates the formation of a collagenous extracellular matrix and synthesis of several osteoblast-related proteins. We recently showed that ascorbic acid dramatically increases alkaline phosphatase and osteocalcin mRNAs and that this induction is blocked by inhibitors of collagen triple-helix formation (Franceschi and Iyer, J Bone Miner Res 7:235). In the present study, the relationship between collagen matrix formation and osteoblast-specific gene expression is explored in greater detail. Kinetic studies revealed that ascorbic acid increased proline hydroxylation in the intracellular procollagen pool within 1 h and stimulated the cleavage of type I collagen propeptides beginning at 2.5 h. Mature alpha 1(I) and alpha 2(I) collagen components were first detected at 10 h and continued to increase in both cell layer and culture medium for up to 72 h. Ascorbic acid also increased the rate of procollagen secretion from cell layers to culture medium. The secretion of another matrix protein, fibronectin, was only slightly affected. Alkaline phosphatase or its mRNA was first detected 2-3 days after ascorbic acid addition, but osteocalcin mRNA was not seen until day 6. Two inhibitors of collagen triple-helix formation, ethyl-3,4-dihydroxybenzoate and 3,4-dehydroproline, inhibited procollagen hydroxylation and alkaline phosphatase induction. 3,4-Dehydroproline also inhibited the induction of alkaline phosphatase and osteocalcin mRNAs. Surprisingly, induction was not blocked if cells were exposed to ascorbic acid before inhibitor addition. Alkaline phosphatase was also partially inhibited if cells were grown in the presence of purified bacterial collagenase. These results indicate that the induction of osteoblast markers by ascorbic acid does not require the continuous hydroxylation and processing of procollagens and suggest that a stable, possibly matrix-associated signal is generated at early times after ascorbic acid addition that allows subsequent induction of osteoblast-related genes.
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PMID:Effects of ascorbic acid on collagen matrix formation and osteoblast differentiation in murine MC3T3-E1 cells. 807 60

Of TGF-beta superfamily proteins, BMP-2 enhanced alkaline phosphatase (ALP) activity in cultured osteoblastic cells, MC3T3-E1, to the same level promoted by ascorbate, whereas TGF-beta s (beta 1, beta 2, beta 3) reduced ALP activity and altered cell morphology under the same conditions. Activin appeared to have no distinct effect on ALP synthesis. Ascorbate dependent increase in ALP synthesis was markedly stimulated in the presence of BMP-2. The synergistic effect of ascorbate on ALP synthesis was replaced by type I collagen coated on the culture dish. However, BMP-2 appeared not to bind to type I collagen. These findings indicate that BMP-2 acts directly on osteoblastic cells through its receptors and collagenous matrix can neither recruit BMP-2 nor modulate directly the action of BMP-2 in the pericellular area. Treatment of cells grown in ascorbate media with TGF-beta s decreased rapidly the cellular ALP activity indicating that TGF-beta s direct cells to the dedifferentiated stage.
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PMID:Synergistic effect of BMP-2 and ascorbate on the phenotypic expression of osteoblastic MC3T3-E1 cells. 897 78


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