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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)

The inorganic pyrophosphatase (PPiase) activity was determined by a colorimetric method in the odontoblasts and the parts of the enamel organ related to enamel matrix formation and enamel maturation. The effects on PPi hydrolysis by EDTA, R 8231, urea and heat treatment were found to be almost identical to those reported for nonspecific alkaline phosphatase (APase) in the same tissues. The Mg2+ activation curve for PPiase was also similar. Like those of APase, these characteristics of PPiase activity were identical in the three locations studied. It is suggested that the close similarity in the properties of PPiase and APase is due to activity of the same enzyme, a concept which is in agreement with recent biochemical and histochemical studies of calcification.
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PMID:Inorganic pyrophosphatase in isolated enamel organ and odontoblasts from the rat incisor. 0 71

Some of the characteristics of the pyrophosphatase and ATPase activities studied in isolated cartilage matrix vesicles were found to be similar to those already reported for the solubilized and purified bone alkaline phosphatase. Thus, the pH optimum of the pyrophosphatase activity responded similarly to changes in the concentration of Mg2+, Ca2+, and PPi. Further, the ATPase activity was not activated by Ca2+ in the presence of an optimal Mg2+ concentration. It is proposed that a function of the alkaline phosphatase of matrix vesicles in vivo is to hydrolyze the substrates PPi, ADP, and ATP, which are known inhibitors of calcium phosphate precipitation.
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PMID:Pyrophosphatase and ATPase of isolated cartilage matrix vesicles. 1 78

The Ca2+-binding glycoprotein isolated from preosseous cartilage shows also alkaline phosphatase activity. The purification procedure indicates that the enzyme is inhibited in crude extract and conceivably in the intact tissue; the activity may be controlled by the proteoglycans present in the matrix. Other substrates are hydrolyzed by the purified enzyme in addition to p-nitrophenylphosphate; the highest specific activity was measured with ATP and pyrophosphate (PPi) at pH 7.5 and 9.0 Mg2+ induces an activation of ATP and PPi hydrolysis; Ca2+ activates hydrolysis of ATP but inhibits that of PPi. The glycoprotein shows also transphosphorylase activity, L-serine being the best phosphate acceptor. The release or transfer of Pi catalyzed by the glycoprotein can be an important step in calcium phosphate precipitation.
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PMID:Enzymatic properties of the Ca2+-binding glycoprotein isolated from preosseous cartilage. 11 41

Rats were fed a low calcium diet deficient in vitamin D for 14 days. Changes in alkaline phosphatase activities in odontoblasts dissected out from incisor teeth were studied biochemically. A strong increase in pNPP-ase, PPi-ase, total ATP-degradation and Ca2+- ATPase was observed in the deficient animals compared with animals fed a control diet.
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PMID:Odontoblast metabolism in rats deficient in vitamin D and calcium. II. Changes in activities of alkaline phosphatases. 14 75

The same isoenzyme of nonspecific alkaline phosphatase (APase), assayed with p-nitrophenylphosphate (p-NPP), was shown be present in different calcifying tissues, bone, calcifying cartilage, odontoblasts and enamel organ. Indications were also found that the enzymatic degradation of inorganic pyrophosphate (PPi) in calcifying tissues is mediated by APase. By using specific APase inhibitors, it was shown that two enzymes capable of degrading ATP exist. These were characterized in dentinogenically active odontoblasts, and it was concluded that one is the classical APase, the other is a Ca2+ and Mg2+ activated ATPase, named Ca2+-ATPase. The two phosphatases were solubilized from odontoblasts and separated. The localization of APase and Ca2+-ATPase in odontoblasts was investigated by subcellular fractionation and EM histochemistry. Routine methods for fixation were found to almost completely inactivate the enzymes. By using a mild fixation technique that preserved 80% of the enzyme activity, the main localization for both APase and Ca2+-ATPase was found to be in the membranes of intercellular vesicles located in the cell body and odontoblasts process. No activity was found in the cell membranes. It is concluded that there are at least two enzymes able to degrade phosphate compounds at alkaline pH in hard tissue forming cells. One is the nonspecific alkaline phosphatase (APase; EC 3. 1. 3. 1), which is active against p-NPP, PPi, glycerophosphates and ATP among other substrates. The other is a more specific Ca2+-ATPase (EC 3. 6. 1. 3). There seems to be an intimate relation between these two enzymes in the tissue. The function of APase in biological calcification is still obscure. In contrast, the finding of an ATP dependent, intravesicularly directed, transmembranous Ca2+-transport in vesicles derived from the microsomal fraction of odontoblasts may explain the role of Ca2+-ATPase.
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PMID:Odontoblast alkaline phosphatases and Ca2+ transport. 15 9

Ca2+-ATPase activity was solubilized, partly purified, and separated from nonspecific alkaline phosphatase activity (APase1) of dentinogenically active rat incisor odontoblasts. Attempts were made to extract the enzymes by various agents, such as Triton X-100, deoxycholate, butanol, EDTA, and buffers of decreasing ionic strength. Solubilization by butanol followed by extraction with low concentrations of EDTA proved to be most effective. Purification and separation were done by molecular sieve chromatography. Ca2+-ATPase showed no activity against p-nitrophenyl phosphate (p-NPP) or inorganic pyrophosphate (PPi) and was unaffected by R 8231 [+/-)-6(m-bromophenyl)-5,6-dihydroimidazo(2,1-b)thiazole oxalate]. It was activated by Ca2+ and Mg2+ ions in equimolar concentrations with the substrate. The enzyme was rapidly inactivated in the solubilized state. An apparent molecular weight of about 18,000 was obtained from molecular sieve data. APase, showing activity against ATP, PPi, and p-NPP, was virtually totally inhibited by R 8231. It was activated by Mg2+ ions but slightly reduced in activity by Ca2+ ions. It had an apparent mol. wt. of 79,000. The results provide direct evidence for earlier suggestions of the existence in hard tissue forming cells of two phosphatases active at alkaline pH.
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PMID:Separation of odontoblast Ca2+-ATPase and alkaline phosphatase. 15 25

4-Nitrophenyl and 2-napthyl monoesters of phenylphosphonic acid have been synthesized, and an enzyme catalyzing their hydrolysis was resolved from alkaline phosphatase of a commerical calf intestinal alkaline phosphatase preparation by extensive ion-exchange chromatography, chromatography on L-phenylalanyl-Sepharose with a decreasing gradient of (NH4) 2SO4, and gel filtration. Detergent-solubilized enzyme from fresh bovine intestine was purified after (NH4)2SO4 fractionation by the same technique. The purified enzyme is homogeneous by polyacrylamide gel electrophoresis and sedimentation equilibrium centrifugation. It has a molecular weight of 108,000, contains approximately 21% carbohydrate, and has an amino acid composition considerably different from that reported from alkaline phosphatase from the same tissue. The homogeneous intestinal enzyme, an efficient catalyst of phosphonate ester hydoolysis but not of phosphate monoester hydrolysis, was identified as a 5'-nucleotide phosphodiesterase by its ability to hydrolyze 4-nitrophenyl esters of 5'-TMP but not of 3'-TMP. Also consistent with this identification was the ability of the enzyme to hydrolyze 5'-ATP to 5'-AMP and PPi, NAD+ to 5'-AMP and NMN, TpT to 5'-TMP and thymidine, pApApApA to 5'-AMP, and only the single-stranded portion of tRNA from the 3'-OH end. Snake venom 5'-nucleotide phosphodiesterase also hydrolyzes phosphonate esters, but 3'-nucleotide phosphodiesterase of spleen and cyclic 3',5'-AMP phosphodiesterase do not. Thus, types of phosphodiesterases can be conveniently distinguished by their ability to hydrolyze phosphonate esters. As substrates for 5'-nucleotide phosphodiesterases, phosphonate esters are preferable to the more conventional esters of nucleotides and bis(4-nitrophenyl) phosphate because of their superior stability and ease of synthesis. Furthermore, the rate of hydrolysis of phosphonate esters under saturating conditions is greater than that of the conventional substrates. At substrate concentrations of 1 mM the rates of hydrolysis of phosphonate esters and of nucleotide esters are comparable and both superior to that of bis(4-nitrophenyl) phosphate.
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PMID:Hydrolysis of phosphonate esters catalyzed by 5'-nucleotide phosphodiesterase. 17 Sep 64

The distribution of calcium pyrophosphate mineral phase, almost exclusively confined to articular cartilage in chondrocalcinosis, and the high level of pyrophosphate (PPi) ion relative to serum in synovial fluid in patients with either chondrocalcinosis or advanced osteoarthritis led to an investigation of whether cartilage cells elaborate PPi ions. Incubates of articular cartilage from young rabbits but not from mature rabbits, as well as growth plates cartilage, released PPi into incubation media during a 4h period. Control rabbit ear cartilage and synovial membrane elaborated negligible amounts of PPi. The PPi was shown to be undialyzable but could be dissociated from the alkaline phosphatase by ultracentrifugation. In 16 patients with osteoarthritis, a substantial output of PPi by samples of articular cartilage from the knee was demonstrated. It is postulated that either rapid cell division and matrix synthesis found in the base of ulcerating osteoarthritic cartilage or remodeling calcified sites are the source of the PPi in such osteoarthritic cartilage. It is further hypothesized that this PPi output accounts at least in part for the elevated PPi levels found in synovial fluid of patients with osteoarthritis.
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PMID:Extrusion of pyrophosphate into extracellular media by osteoarthritic cartilage incubates. 17 32

Incubates of articular cartilage from young but not mature rabbits, as well as growth plate cartilage, elaborated PPi into basel Eagle's medium during a 4-hour period. Control rabbit synovial membrane and ear cartilage elaborated negligible amounts of PPi. The PPi was shown to be nondialyzable but could be dissociated from the alkaline phosphatase by ultracentrifugation. In 16 patients with osteoarthritis a substantial output of PPi by samples of articular cartilage from the knee was demonstrated. The present authors believe that either rapid cell division and matrix synthesis found in the base of ulcerating osteoarthritic cartilage or remodeling calcified sites comprise the origin of the PPi in such osteoarthritic cartilage. They further theorize that this PPi output accounts for a considerable fraction, if not all, of the elevated PPi levels found in synovial fluid of patients with osteoarthritis.
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PMID:Pyrophosphate release by osteoarthritis cartilage incubates. 18 Oct 24

Accumulation of 99m Tc-Sn-pyrophosphate in pleural effusions has been evaluated in 56 patients grouped as follows: 8 with bacterial effusion (Group A), 27 with malignant effusion treated by local and/or parenteral antitumor chemotherapy (Group B), 21 with malignant effusion treated only by supportive therapy (Group C). Results, expressed as effusion to plasma PPi ratio, ranged from 0.1 to 0.28 in group A, from 0.04 to 0.64 in group B and from 0.60 to 1.73 in group C, with significant differences among the three groups. In no case was uptake found in cells of the sediment. Chemical analysis (including total and ionized calcium, total protein, acid and alkaline phosphatase) of plasma and exudate in neoplastic patients showed a slight, but significant, difference between groups B and C as regards plasma-effusion gradient for total calcium and acid phosphatase. Negative correlation also exists between effusion to plasma PPi ratio and plasma-exudate gradient for ionized calcium in neoplastic patients. The data support the hypothesis that acid phosphatase content and calcium gradient are among the factors involved in the mechanism of PPi accumulation in pleural effusions.
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PMID:Accumulation of 99m Tc-Sn-pyrophosphate in pleural effusions. 21 4


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