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PubMed1991

Alkaline phosphatase prevents platelet stimulation by thromboxane-mimetics.

1. The effects of alkaline phosphatase on platelet aggregation, secretion and thromboxane B2 (TxB2) generation induced by the full dose-range of common platelet agonists were studied in human platelet-rich plasma and washed platelets. 2. Platelet aggregation and adenosine 5'-triphosphate (ATP) secretion induced by threshold and supramaximal concentrations of arachidonate and stable TxA2 and prostaglandin endoperoxide-mimetics (compounds U46619 and EP171) were abolished in the presence of alkaline phosphatase (0.5-1 u ml-1), even though the synthesis of TxB2 persisted. In contrast, platelet aggregation by PAF-acether and by supramaximal concentrations of thrombin as well as the primary wave of aggregation by adenosine diphosphate (ADP) and adrenaline were unaffected by alkaline phosphatase under conditions where the secondary wave of aggregation by ADP was blocked. 3. Alkaline phosphatase, unlike prostacyclin, failed to raise the adenosine 3':5'-cyclic monophosphate (cyclic AMP) content of the platelets. Also, the pretreatment of platelets by inorganic phosphate or by ATP plus creatine phosphate/creatine phosphokinase reversed the inhibitory effect of alkaline phosphatase. 4. Experiments performed in the guinea-pig in vivo showed that alkaline phosphatase was effective on thrombocytopenia induced by arachidonate. 5. Our results provide the first direct evidence for a specific inhibitory effect of alkaline phosphatase at a site sensitive to TxA2 and prostaglandin endoperoxides and suggest that its phosphorylation/dephosphorylation state may play an important role in modulating platelet activation. These results also suggest the presence of ecto-protein kinases on membrane platelets.

Alkaline Phosphatase↗
PubMed1994

Evidence of alkaline phosphatase interference in a zidovudine radioimmunoassay.

Phosphorylated zidovudine (ZDV) concentrations may provide a link between drug exposure and clinical efficacy since these would include the active, intracellular form of the drug, ZDV triphosphate. Many groups are investigating the optimal methodology that can be used to accomplish this goal. The initial purpose of the present studies was to examine the effect of the inclusion of cell wash steps on the quantitation of intracellular ZDV. Ten milliliters of whole blood collected from healthy volunteers was spiked with increasing ZDV concentrations (0.187, 0.375, 1.87, and 3.75 microM), allowed to equilibrate at room temperature for 1 h, and separated into whole-blood components by a density gradient procedure. A mononuclear cell pellet was obtained, reconstituted with 2 ml of phosphate-buffered saline (PBS), and split into two aliquots, one of which was not washed at all and the other of which was washed four times with 1 ml of PBS. All samples were analyzed by ZDV radioimmunoassay (RIA) after a 1:1 dilution with either 1 mg of alkaline phosphatase (type 1-S; Sigma) per ml or PBS. Parent ZDV was measured in those samples which were not treated with the enzyme, while total ZDV was measured in those samples which were exposed to alkaline phosphatase (21 degrees C for 1 h). The result of the difference between the two samples is total phosphorylated ZDV. During the experiment, evidence of alkaline phosphatase interference with the RIA became apparent, confusing interpretation of intracellular ZDV concentrations. This evidence was based on three sets of data. First, wash samples showed increases in ZDV concentrations of as great as 0.127 microgramM after exposure to alkaline phosphatase, even though on microscopic inspection the wash samples were acellular. Second, the sum of total ZDV recovered from the four wash samples plus the washed cell pellet was as much as 14-fold greater than the total ZDV measured in the unwashed cell pellet. Theoretically, at least, these two entities should be equal. Finally, control samples of alkaline phosphatase in PBS (0.5 mg/ml) run directly through the assay measured false ZDV levels ranging from 0.002 to 0.075 microgramM (0.6 to 20 ng/ml). Alkaline phosphatase is frequently used to measure phosphorylated anabolites of ZDV in peripheral blood mononuclear cells. These data show that the particular form of alkaline phosphatase used may interfere with the ZDV RIA and may confuse the interpretation of phosphorylated anabolite concentrations of ZDV.

Alkaline Phosphatase↗
PubMed1984

Production of two phosphatases by Lysobacter enzymogenes and purification and characterization of the extracellular enzyme.

Lysobacter enzymogenes produces an extracellular phosphatase (EC. 3.1.3.1) during the stationary phase of growth. The cells also produce a cell-associated alkaline phosphatase. This enzyme is found in the particulate fraction of cell extracts and may be membrane bound. The production of both phosphatases, especially the extracellular enzyme, is reduced by inorganic phosphate. The extracellular phosphatase was purified to a specific activity of 270 U/mg primarily by chromatography on carboxymethyl cellulose and gel filtration. The enzyme is stable under normal storage conditions but is rapidly inactivated above 70 degrees. It consists of one polypeptide with an approximate molecular weight of 25,000. The pH optimum is 7.5, and the Km for p-nitrophenylphosphate is 2.2 X 10(-4) M. The enzyme degrades a number of other phosphomonoesters but at a reduced rate compared with the rate obtained with p-nitrophenylphosphate. Phosphate and arsenate inhibit the enzyme, but EDTA and other chelating agents have no effect. The lack of a metal ion requirement for activity, the lower molecular weight, the soluble nature of the enzyme, and the lower pH optimum clearly distinguish the extracellular phosphatase from the cell-associated phosphatase and from other bacterial phosphatases.

Alkaline Phosphatase↗
PubMed2001

Colorimetric immuno-protein phosphatase inhibition assay for specific detection of microcystins and nodularins of cyanobacteria.

A novel immunoassay was developed for specific detection of cyanobacterial cyclic peptide hepatotoxins which inhibit protein phosphatases. Immunoassay methods currently used for microcystin and nodularin detection and analysis do not provide information on the toxicity of microcystin and/or nodularin variants. Furthermore, protein phosphatase inhibition-based assays for these toxins are not specific and respond to other environmental protein phosphatase inhibitors, such as okadaic acid, calyculin A, and tautomycin. We addressed the problem of specificity in the analysis of protein phosphatase inhibitors by combining immunoassay-based detection of the toxins with a colorimetric protein phosphatase inhibition system in a single assay, designated the colorimetric immuno-protein phosphatase inhibition assay (CIPPIA). Polyclonal antibodies against microcystin-LR were used in conjunction with protein phosphatase inhibition, which enabled seven purified microcystin variants (microcystin-LR, -D-Asp3-RR, -LA, -LF, -LY, -LW, and -YR) and nodularin to be distinguished from okadaic acid, calyculin A, and tautomycin. A range of microcystin- and nodularin-containing laboratory strains and environmental samples of cyanobacteria were assayed by CIPPIA, and the results showed good correlation (R2 = 0.94, P < 0.00001) with the results of high-performance liquid chromatography with diode array detection for toxin analysis. The CIPPIA procedure combines ease of use and detection of low concentrations with toxicity assessment and specificity for analysis of microcystins and nodularins.

Bacterial Toxins↗
PubMed1985

Intracellular acid phosphatase content and ability of different macrophage populations to kill Nocardia asteroides.

It has been reported that the activity of lysosomal acid phosphatase decreases inversely with numbers of ingested virulent Nocardia spp. in normal murine peritoneal and alveolar macrophages. These studies suggested that this relationship correlated with the effectiveness of these macrophage populations in killing Nocardia asteroides. Experiments were designed to determine if acid phosphatase activity is affected by infection with N. asteroides in four different macrophage populations isolated from normal and nocardia-immunized mice. Macrophages were also tested simultaneously for their ability to kill N. asteroides. Peritoneal, alveolar, and splenic macrophages and Kupffer cells were infected in vitro with strains of N. asteroides of differing virulence. Uptake and killing assays were performed. Acid phosphatase levels and numbers of intracellular nocardiae were quantitated in the same macrophages, using a computer-assisted cytophotometry system. Acid phosphatase activity decreased inversely with numbers of intracellular nocardiae in macrophages that could not kill or inhibit this pathogen. Acid phosphatase activity was not significantly changed in macrophages that inhibited growth of, but did not kill, N. asteroides, whereas activity was increased or enhanced in macrophages that killed most of the ingested nocardiae. The order of nocardicidal effectiveness (and resistance to enzyme activity reduction with infection) for normal macrophages was splenic greater than peritoneal greater than alveolar greater than Kupffer. In contrast, the order of these two parameters for macrophages isolated from immunized mice was Kupffer greater than peritoneal greater than alveolar greater than splenic. These results demonstrate that lysosomal acid phosphatase activity is an effective marker of the ability of macrophages to inhibit growth of and kill N. asteroides and that macrophages isolated from different anatomical sites differ functionally from each other with respect to nocardicidal and acid phosphatase activities.

Acid Phosphatase↗
PubMed1988

Acid phosphatase activity of virulent and avirulent clones of Leishmania donovani promastigotes.

Virulent and avirulent clones of Leishmania donovani promastigotes were examined for their acid phosphatase activity. The acid phosphatase activity of whole-cell lysates of virulent clones was 1.5 to 2.0 times higher than that of avirulent clones. Pellet fractions (260,000 x g, 30 min) from sonicated promastigotes of a virulent clone and an avirulent clone contained 60 and 40% of the total enzyme activity, respectively. Membrane-bound acid phosphatase was extracted with Triton X-100 from the pellet. This membrane-bound phosphatase activity was 2.4-fold higher in virulent organisms than in avirulent organisms. The membrane acid phosphatase exhibited two distinct bands on polyacrylamide gels stained for enzyme activity. One diffuse, faster-migrating band showed identical electrophoretic mobility in both virulent and avirulent clones, although a higher enzymatic activity was observed with the extract from virulent cells. In contrast, a slower-migrating band was different between the two clones in the mobility. These results suggest that membrane-bound acid phosphatase was quantitatively and qualitatively different between virulent and avirulent promastigotes of L. donovani. In addition, virulent cells produced a relatively high level of acid phosphatase throughout the growth in culture.

Acid Phosphatase↗
PubMed1973

Inorganic phosphate transport in Escherichia coli: involvement of two genes which play a role in alkaline phosphatase regulation.

Two classes of alkaline phosphatase constitutive mutations which comprise the original phoS locus (genes phoS and phoT) on the Escherichia coli genome have been implicated in the regulation of alkaline phosphatase synthesis. When these mutations were introduced into a strain dependent on a single system, the pst system, for inorganic phosphate (P(i)) transport, profound changes in P(i) transport were observed. The phoT mutations led to a complete P(i) (-) phenotype in this background, and no activity of the pst system could be detected. The introduction of the phoS mutations changed the specificity of the pst system so that arsenate became growth inhibitory. Changes in the phosphate source led to changes in the levels of constitutive alkaline phosphatase synthesis found in phoS and phoT mutants. When glucose-6-phosphate or l-alpha-glycerophosphate was supplied as the sole source of phosphate, phoT mutants showed a 3- to 15- fold reduction in constitutive alkaline phosphatase synthesis when compared to the maximal levels found in limiting P(i) media. However, these levels were still 100 times greater than the basal level of alkaline phosphatase synthesized in wild-type strains under these conditions. The phoS mutants showed only a two- to threefold reduction when grown with organic phosphate sources. The properties of the phoT mutants selected on the basis of constitutive alkaline phosphatase synthesis were similar in many respects to those of pst mutants selected for resistance to growth inhibition caused by arsenate. It is suggested that the phoS and phoT genes are primarily involved in P(i) transport and, as a result of this function, play a role in the regulation of alkaline phosphatase synthesis.

Alkaline Phosphatase↗
PubMed1974

Biochemical localization of alkaline phosphatase in the cell wall of a marine pseudomonad.

The various layers of the cell envelope of marine pseudomonad B-16 (ATCC 19855) have been separated from the cells and assayed directly for alkaline phosphatase activity under conditions established previously to be optimum for maintenance of the activity of the enzyme. Under conditions known to lead to the release of the contents of the periplasmic space from the cells, over 90% of the alkaline phosphatase was released into the medium. Neither the loosely bound outer layer nor the outer double-track layer (cell wall membrane) showed significant activity. A small amount of the alkaline phosphatase activity of the cells remained associated with the mureinoplasts when the outer layers of the cell wall were removed. Upon treatment of the mureinoplasts with lysozyme, some alkaline phosphatase was released into the medium and some remained with the protoplasts formed. Cells washed and suspended in 0.5 M NaCl were lysed by treatment with 2% toluene, and 95% of the alkaline phosphatase in the cells was released into the medium. Cells washed and suspended in complete salts solution (0.3 M NaCl, 0.05 M MgSO(4), and 0.01 M KCl) or 0.05 M MgSO(4) appeared intact after treatment with toluene but lost 50 and 10%, respectively, of their alkaline phosphatase. The results suggest that the presence of Mg(2+) in the cell wall is necessary to prevent disruption of the cells by toluene and may also be required to prevent the release of alkaline phosphatase by toluene when disruption of the cells by toluene does not take place.

Alkaline Phosphatase↗
PubMed1977

Biochemical localization of the alkaline phosphatase of Bacillus licheniformis as a function of culture age.

Biochemical localization of the enzyme as a function of age of cell culture showed the alkaline phosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.1) activity of Bacillus licheniformis MC14 predominantly in the particulate cell fraction in early- and mid-log cells. However, in late-log and stationary cells, increasing amounts of activity were found in the soluble fraction of lysed cells. Upon protoplast formation of these cells, the activity was released into the soluble fraction. No alkaline phosphatase activity was found in either the cytoplasmic fraction or in the cell medium during any phase of cell growth. The soluble fraction released on protoplast formation that contained alkaline phosphatase activity showed immunological cross-reactivity with antibody to the purified heat--salt-solubilized membrane alkaline phosphatase (F. M. Hulett-Cowling and L. L. Campbell, 1971). Theparticulate membrane fraction containing a firmly associated alkaline phosphatase also showed similar cross-reactivity. Further, the effectiveness of nonionic detergents, ionic detergents, bile salts, and various concentrations of magnesium and sodium as solubilizing agents for this membrane-bound alkaline phosphatase was investigated. Hexadecyl pyridinium chloride (0.03 M) and magnesium and sodium salts (above 0.2 M) were effective solubilizing agents. The substrate specificities of the various fractions were determined and compared to the substrate specificities of the purified membrane alkaline phosphatase.

Alkaline Phosphatase↗
PubMed1980

Kinetics and regulation of cell-free alkaline phosphatase synthesis.

Regulation of alkaline phosphatase (EC 3.1.3.1) synthesis in a cell-free system from Escherichia coli has been observed. Synthesis from transducing phage deoxyribonucleic acid templates carrying phoA+ occurred in S30 fractions from wild-type or alkaline phosphatase-constitutive mutants. It did not occur in S30) fractions from alkaline phosphatase-negative mutants (phoB). The hybrid gene phoA-lacZ was also subject to phoB control, implying that phoA transcription is regulated. The yield of active alkaline phosphatase per phoA+ gene copy from cell-free synthesis was similar to that of beta-galactosidase. Alkaline phosphatase activity took longer to appear than beta-galactosidase activity. Synthesis of alkaline phosphatase subunits was not delayed, suggesting that a minimum number of subunits are synthesized before formation of active alkaline phosphatase occurs.

Alkaline Phosphatase↗
PubMed1981

Lactoperoxidase-125I localization of salt-extractable alkaline phosphatase on the cytoplasmic membrane of Bacillus licheniformis.

Previous histochemical and biochemical localizations of alkaline phosphatase in Bacillus licheniformis MC14 have shown that the membrane-associated form of the enzyme is located on the inner surface of the cytoplasmic membrane, and soluble forms are located in the periplasmic space and in the growth medium. The distribution of salt-extractable alkaline phosphatase on the surfaces of the cytoplasmic membrane of B. licheniformis MC14 was determined by using lactoperoxidase-125I labeling techniques. Cells harvested during rapid alkaline phosphatase production were converted to protoplasts or lysed protoplasts and labeled. Analysis of the data obtained indicated that 30% of the salt-extractable, membrane-associated alkaline phosphatase was located on the outer surface of the cytoplasmic membrane, whereas 70% of the membrane-associated enzyme was localized on the inner surface. Controls for protoplast integrity (release of tritiated thymidine or examination of cytoplasmic proteins for label content) indicated excellent protoplast stability. Controls indicated that chemical labeling was not a factor in the apparent distribution of alkaline phosphatase on the membrane. These results support the previously reported histochemical localization of alkaline phosphatase on the membrane inner surface. The presence of alkaline phosphatase on the membrane outer surface is reasonable, considering the soluble forms of the enzyme found in the periplasmic region and in the culture medium.

Alkaline Phosphatase↗
PubMed1983

Multiple genes for membrane-bound phosphatases in Escherichia coli and their action on phospholipid precursors.

We have devised a coupled radiochemical assay for detecting phosphatidylglycerolphosphate (PGP) phosphatase activity in Escherichia coli colonies immobilized on filter paper. There appeared to be at least two enzymes capable of dephosphorylating PGP, as judged by the characterization of mutations in two genes designated pgpA and pgpB. The former is located near min 10 and is cotransducible with proC and dnaZ. The latter is situated near min 28 and is closely linked to cysB. The available mutant alleles of pgpA reduced the specific activity of PGP phosphatase in crude extracts by about 30%, but they had no effect on phosphatidic acid (or lysophosphatidic acid) phosphatase. Mutants altered in the pgpB locus inactivated most of the residual PGP phosphatase activity present in single-step pgpA mutants, and the level of phosphatidic acid phosphatase was also reduced 20-fold. The available mutations in pgpA and pgpB elevated the cellular PGP pool by 10- to 50-fold. The maximal PGP levels never exceeded 5%, and these strains were not conditionally lethal. The simplest interpretation of our findings is that there are at least two membrane-associated phosphatases in E. coli, both distinct from alkaline phosphatase. The pgpA gene product is specific for PGP, whereas the pgpB gene product also acts on phosphatidic acid and lysophosphatidic acid.

Cell Membrane↗
PubMed1988

Regulation of phosphatidate phosphatase activity by inositol in Saccharomyces cerevisiae.

Regulation of phosphatidate phosphatase (EC 3.1.34) activity was examined in Saccharomyces cerevisiae cells supplemented with phospholipid precursors. Addition of inositol to the growth medium of wild-type cells resulted in a twofold increase in phosphatidate phosphatase activity. The increase in phosphatidate phosphatase activity was not due to soluble effector molecules, and inositol did not have a direct effect on enzyme activity. The phosphatidate phosphatase activity associated with the mitochondrial, microsomal, and cytosolic fractions of the cell was regulated by inositol in the same manner. Cells supplemented with inositol had elevated phospholipid levels and reduced triacylglycerol levels compared with unsupplemented cells. Serine, ethanolamine, and choline did not significantly affect the phosphatidate phosphatase activity of cells grown in the absence or presence of inositol. Enzyme activity was not regulated in inositol biosynthesis regulatory mutants, suggesting that regulation by inositol is coupled to regulation of inositol biosynthesis. Phosphatidate phosphatase activity was pleiotropically expressed in structural gene mutants defective in phospholipid biosynthesis. These results suggested that phosphatidate phosphatase was regulated by inositol at a genetic level.

Culture Media↗
PubMed2000

Cloning and characterization of secretory tyrosine phosphatases of Mycobacterium tuberculosis.

Two genes with sequence homology to those encoding protein tyrosine phosphatases were cloned from genomic DNA of Mycobacterium tuberculosis H(37)Rv. The calculated molecular masses of these two putative tyrosine phosphatases, designated MPtpA and MPtpB, were 17. 5 and 30 kDa, respectively. MPtpA and MPtpB were expressed as glutathione S-transferase fusion proteins in Escherichia coli. The affinity-purified proteins dephosphorylated the phosphotyrosine residue of myelin basic protein (MBP), but they failed to dephosphorylate serine/threonine residues of MBP. The activity of these phosphatases was inhibited by sodium orthovanadate, a specific inhibitor of tyrosine phosphatases, but not by okadaic acid, an inhibitor of serine/threonine phosphatases. Mutations at the catalytic site motif, cysteine 11 of MPtpA and cysteine 160 of MPtpB, abolished enzyme activity. Southern blot analysis revealed that, while mptpA is present in slow-growing mycobacterial species as well as fast-growing saprophytes, mptpB was restricted to members of the M. tuberculosis complex. These phosphatases were present in both whole-cell lysates and culture filtrates of M. tuberculosis, suggesting that these proteins are secreted into the extracellular medium. Since tyrosine phosphatases are essential for the virulence of several pathogenic bacteria, the restricted distribution of mptpB makes it a good candidate for a virulence gene of M. tuberculosis.

Amino Acid Sequence↗
PubMed1992

Protein tyrosine phosphatase containing SH2 domains: characterization, preferential expression in hematopoietic cells, and localization to human chromosome 12p12-p13.

Protein tyrosine phosphorylation has been implicated in the growth and functional responses of hematopoietic cells. Recently, approaches have been developed to characterize the protein tyrosine phosphatases that may contribute to regulation of protein tyrosine phosphorylation. One novel protein tyrosine phosphatase was expressed predominantly in hematopoietic cells. Hematopoietic cell phosphatase encodes a 68-kDa protein that contains a single phosphatase conserved domain. Unlike other known protein tyrosine phosphatases, hematopoietic cell phosphatase contains two src homology 2 domains. We also cloned the human homolog, which has 95% amino acid sequence identity. Both the murine and human gene products have tyrosine-specific phosphatase activity, and both are expressed predominantly in hematopoietic cells. Importantly, the human gene maps to chromosome 12 region p12-p13. This region is associated with rearrangements in approximately 10% of cases of acute lymphocytic leukemia in children.

Amino Acid Sequence↗
PubMed2000

The yeast inositol polyphosphate 5-phosphatases inp52p and inp53p translocate to actin patches following hyperosmotic stress: mechanism for regulating phosphatidylinositol 4,5-bisphosphate at plasma membrane invaginations.

The Saccharomyces cerevisiae inositol polyphosphate 5-phosphatases (Inp51p, Inp52p, and Inp53p) each contain an N-terminal Sac1 domain, followed by a 5-phosphatase domain and a C-terminal proline-rich domain. Disruption of any two of these 5-phosphatases results in abnormal vacuolar and plasma membrane morphology. We have cloned and characterized the Sac1-containing 5-phosphatases Inp52p and Inp53p. Purified recombinant Inp52p lacking the Sac1 domain hydrolyzed phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P(2)] and PtdIns(3, 5)P(2). Inp52p and Inp53p were expressed in yeast as N-terminal fusion proteins with green fluorescent protein (GFP). In resting cells recombinant GFP-tagged 5-phosphatases were expressed diffusely throughout the cell but were excluded from the nucleus. Following hyperosmotic stress the GFP-tagged 5-phosphatases rapidly and transiently associated with actin patches, independent of actin, in both the mother and daughter cells of budding yeast as demonstrated by colocalization with rhodamine phalloidin. Both the Sac1 domain and proline-rich domains were able to independently mediate translocation of Inp52p to actin patches, following hyperosmotic stress, while the Inp53p proline-rich domain alone was sufficient for stress-mediated localization. Overexpression of Inp52p or Inp53p, but not catalytically inactive Inp52p, which lacked PtdIns(4,5)P(2) 5-phosphatase activity, resulted in a dramatic reduction in the repolarization time of actin patches following hyperosmotic stress. We propose that the osmotic-stress-induced translocation of Inp52p and Inp53p results in the localized regulation of PtdIns(3,5)P(2) and PtdIns(4,5)P(2) at actin patches and associated plasma membrane invaginations. This may provide a mechanism for regulating actin polymerization and cell growth as an acute adaptive response to hyperosmotic stress.

Actins↗
PubMed2000

Therapeutic insulin and hepatic glucose-6-phosphatase activity in preterm infants.

BACKGROUND: Hepatic glucose-6-phosphatase activity is low at birth, and in term infants rises rapidly to adult levels. In contrast, in most preterm infants, it remains low postnatally making them vulnerable to repeated hypoglycaemic episodes, resultant cerebral damage, or risk of sudden and unexpected death. AIMS: To investigate the clinical features of preterm infants with low glucose-6-phosphatase enzyme activity to determine the influencing factors. METHODS: Clinical data from 36 preterm infants were correlated by stepwise multiple regression analysis with V(max) of hepatic glucose-6-phosphatase as the dependent variable. RESULTS: The most significant correlation was with the administration of insulin (units/kg/h postnatal life) with lesser effects of respiratory distress syndrome and dopamine administration. The V(max) changes reflected changes in the level of expression of the glucose-6-phosphatase protein. CONCLUSION: In a variety of animal models, hepatic glucose-6-phosphatase levels have been shown to decrease in response to insulin, which also decreases transcription of the glucose-6-phosphatase gene. The association of insulin administration with high levels of hepatic glucose-6-phosphatase activity and protein expression was therefore most unexpected. Results from model systems, or adults, must be extrapolated to the metabolism of preterm infants with caution.

Blood Glucose↗
PubMed2002

Bone mineralisation in premature infants cannot be predicted from serum alkaline phosphatase or serum phosphate.

BACKGROUND: The bone mineral content of premature infants at term is lower than in mature infants at the same postconceptional age. Serum alkaline phosphatase and serum phosphate are often used as indicators of bone mineralisation. OBJECTIVE: To analyse the association between bone mineral content and serum alkaline phosphatase and serum phosphate. METHODS: Serum alkaline phosphatase and phosphate were measured at weekly intervals during admission in 108 premature infants of gestational age below 32 weeks (mean (SD) gestational age 29 (2) weeks; mean (SD) birth weight 1129 (279) g). Bone mineral content was measured at term (mean gestational age 41 weeks) by dual energy x ray absorptiometry and corrected for body size. RESULTS: Serum alkaline phosphatase was significantly negatively associated with serum phosphate (p < 0.001). Bone mineral content was not associated with mean serum alkaline phosphatase (p = 0.8), peak serum alkaline phosphatase (p = 0.5), or mean serum phosphate (p = 0.2) at term. CONCLUSION: Routine measurements of serum alkaline phosphatase and serum phosphate are of no use in predicting bone mineralisation outcome in premature infants.

Absorptiometry, Photon↗