X-ray structure of the 154-amino-acid form of recombinant human basic fibroblast growth factor. comparison with the truncated 146-amino-acid form

The crystal structure of the 154-amino-acid form of human basic fibroblast growth factor (hbFGF154), probably representing the intact form of hbFGF as deduced from the open reading frame of hbFGF cDNA, was determined by X-ray crystallography and refined to a crystallographic residual of 19.0% for all data between 20.0 and 2.0 A resolution. Crystals were obtained from recombinant hbFGF154 expressed in E. coli. hbFGF154 has the same overall structure as the N-terminus truncated 146-amino-acid form. The structure has a Kunitz-type fold and is built of 12 beta-strands of which six antiparallel strands form a beta-sheet barrel. In the structure it was possible to locate two additional residues at the N terminus and the last three C-terminal amino-acid residues, which seem to be disordered in all but one of the reported structures of the truncated form of hbFGF. The C-terminal amino-acid residues are part of the last beta-strand through the formation of a hydrogen bond between the main-chain amide group of Ala152 and the carbonyl O atom of Pro28. An apparent phosphate ion is bound within the basic region on the surface of the molecule and has as ligands the side chains of Asn35, Arg128 and Lys133 and two water molecules. A slightly different hydrogen-bonding pattern to the phosphate ion is observed as compared with the sulfate ions in the truncated forms [Eriksson, Cousens & Matthews (1993). Protein Sci. 2, 1274-1284; Zhang, Cousens, Barr & Sprang (1991). Proc. Natl Acad. Sci. USA, 88, 3446-3450]. One molecule of beta-mercaptoethanol forms a disulfide bridge to Cys77.

Heparin-binding protein (HBP/CAP37): a missing link in neutrophil-evoked alteration of vascular permeability

Polymorphonuclear leukocyte infiltration into tissues in host defense and inflammatory disease causes increased vascular permeability and edema formation through unknown mechanisms. Here, we report the involvement of a paracrine mechanism in neutrophil-evoked alteration in endothelial barrier function. We show that upon neutrophil adhesion to the endothelial lining, leukocytic beta2 integrin signaling triggers the release of neutrophil-borne heparin-binding protein (HBP), also known as CAP37/azurocidin, a member of the serprocidin family of neutrophil cationic proteins. HBP induced Ca++-dependent cytoskeletal rearrangement and intercellular gap formation in endothelial-cell monolayers in vitro, and increased macromolecular efflux in microvessels in vivo. Moreover, selective inactivation of HBP prevented the neutrophils from inducing endothelial hyperpermeability. Our data suggest a fundamental role of neutrophil-derived HBP in the vascular response to neutrophil trafficking in inflammation. Targeting this molecule in inflammatory disease conditions offers a new strategy for prevention of endothelial barrier dysfunction caused by misdirected leukocyte activation.

Heparin binding protein increases survival in murine fecal peritonitis

OBJECTIVE

To test the effectiveness of recombinant heparin-binding protein (HBP), a neutrophil-derived multifunctional protein with monocytic-specific properties, in fecal peritonitis and polymicrobial sepsis.

DESIGN

Prospective, controlled animal trial.

SETTING

Animal research laboratory.

SUBJECTS

Swiss Webster mice challenged with cecal ligation and puncture (CLP) and treated with recombinant HBP and 60 mg/kg cefoxitin twice a day.

INTERVENTIONS

HBP was administered to mice at different concentrations and different intervals before and after CLP. Rat albumin (1%) was administered to control animals.

MEASUREMENTS AND MAIN RESULTS

MORTALITY RATE: Survival was increased in mice pretreated intraperitoneally 24 hrs before CLP with 10 microg or 100 microg of HBP without cefoxitin (p = .01, Cox-Mantel log-rank test). Compared with control animals, survival was increased significantly (from 5% to 47%, p = .014) in mice that received cefoxitin and 50 microg ip HBP immediately after CLP, followed by continuous administration of HBP (12 microg/24 hrs). Intravenous administration of HBP (0.1, 1, and 10 microg) at the time of CLP showed an opposite dose effect; low doses (0.1 microg) prolonged early survival, whereas high dose (10 microg) shortened survival (p = .036). Compared with control animals, overall survival was not different. CHEMOTAXIS: Cytospin preparations from peritoneal exudate cells (PECs) 48 hrs after administration of 10 microg and 100 microg ip HBP demonstrated a 1.7-fold increase in the total number of macrophages compared with carrier control (p < .05). PHAGOCYTOSIS: A flow cytometric in vitro assay demonstrated that administration of 10 microg ip HBP alone did not enhance phagocytosis of fluorescent Escherichia coli in PECs. However, 24-hr pretreatment with 10 microg of HBP followed by CLP increased phagocytosis in PECs 1.8-fold compared with the control CLP group (p = .04). RECEPTOR EXPRESSION: CD16/CD32w expression in PECs did not change after HBP or CLP. CD11b and CD18 expression in PECs was increased significantly after CLP compared with PECs from non-CLP-challenged animals (p < .05). Pretreatment with 10 microg of HBP did not further enhance CD11b/CD18 expression in PECs.

CONCLUSIONS

Recombinant HBP increases survival in murine fecal peritonitis. The mechanisms by which HBP reduces septic death are not fully understood, but they include monocyte chemotaxis and increased phagocytosis of E. coli by PECs. Our data suggest that the inflammatory response induced by CLP is important for the effect of HBP to enhance phagocytosis.

Characterization of the biosynthesis, processing, and sorting of human HBP/CAP37/azurocidin

Azurocidin is a multifunctional endotoxin-binding serine protease homolog synthesized during the promyelocytic stage of neutrophil development. To characterize the biosynthesis and processing of azurocidin, cDNA encoding human preproazurocidin was stably transfected to the rat basophilic leukemia cell line RBL-1 and the murine myeloblast-like cell line 32D cl3; cell lines previously utilized to study the related proteins cathepsin G and proteinase 3. After 30 min of pulse radiolabeling, two forms of newly synthesized proazurocidin (34.5 and 37 kDa), differing in carbohydrate content but with protein cores of identical sizes, were recognized. With time, the 34.5-kDa form disappeared, while the 37-kDa form was further processed proteolytically, as judged by digestion with N-glycosidase F. Conversion of high-mannose oligosaccharides into complex forms was shown by acquisition of complete resistance to endoglycosidase H. Radiosequence analysis demonstrated that the amino-terminal seven amino acid propeptide of proazurocidin was removed in a stepwise manner during processing; initial removal of five amino acids was followed by cleavage of a dipeptide. Presence of the protease inhibitors Gly-Phe-diazomethyl ketone, bestatin, or leupeptin inhibited only the cleavage of the dipeptide, thus indicating the involvement of at least two amino-terminal processing enzymes. Translocation of azurocidin to granules was shown by subcellular fractionation. Similar results, with efficient biosynthesis, processing, and targeting to granules in both cell lines, were obtained with a mutant form of human preproazurocidin lacking the amino-terminal heptapropeptide. In conclusion, this investigation is an important addition to our previous studies on related azurophil granule proteins, and provides novel information concerning the biosynthesis and distinctive amino-terminal processing of human azurocidin.

Heparin-binding protein targeted to mitochondrial compartments protects endothelial cells from apoptosis

Neutrophil-borne heparin-binding protein (HBP) is a multifunctional protein involved in the progression of inflammation. HBP is stored in neutrophil granules and released upon stimulation of the cells in proximity to endothelial cells. HBP affects endothelial cells in multiple ways; however, the molecular and cellular mechanisms underlying the interaction of HBP with these cells are unknown. Affinity isolation and enzymatic degradation demonstrated that HBP released from human neutrophils binds to endothelial cell-surface proteoglycans, such as syndecans and glypican. Flow cytometry indicated that a significant fraction of proteoglycan-bound HBP is taken up by the endothelial cells, and we used radiolabeled HBP to determine the internalization rate of surface-bound HBP. Confocal and electron microscopy revealed that internalized HBP is targeted to perinuclear compartments of endothelial cells, where it colocalizes with mitochondria. Western blotting of isolated mitochondria from HBP-treated endothelial cells showed that HBP is present in 2 forms - 28 and 22 kDa. Internalized HBP markedly reduced growth factor deprivation-induced caspase-3 activation and protected endothelial cells from apoptosis, suggesting that uptake and intracellular routing of exogenous HBP to mitochondria contributes to the sustained viability of endothelial cells in the context of locally activated neutrophils.

Endocytosis of heparin-binding protein (CAP37) is essential for the enhancement of lipopolysaccharide-induced TNF-alpha production in human monocytes

Heparin-binding protein (HBP), also known as CAP37, is a proteolytically inactive serine protease homologue that is released from activated granulocytes. However, HBP is not a biologically inactive molecule but rather a multifunctional protein with properties that include the enhancement of LPS-induced TNF-alpha production from monocytes. We have previously demonstrated that HBP is internalized in monocytes. In the current study, we hypothesize that HBP is internalized in monocytes via endocytosis, and this internalization is an important mechanism by which HBP enhances LPS-induced TNF-alpha release. Using whole blood from healthy donors and flow cytometry, we found that colchicine (0.1-10 mM), cytochalasin D (1000 microM), NH4Cl (10-50 mM), and bafilomycin A1 (0.1-3 microM) significantly reduced the affinity of FITC-HBP for CD14-positive monocytes. Using isolated human monocytes and ELISA, we found that colchicine (0.1 mM), cytochalasin D (30 and 300 microM), NH4Cl (30 mM), and bafilomycin A1 (1 microM) significantly reduced the effect of HBP (10 microg/ml) to enhance LPS (10 ng/ml)-induced TNF-alpha release after 24 h. These findings demonstrate that internalization of HBP in monocytes is essential for the enhancement of LPS-induced TNF-alpha release. Transport of HBP to an activating compartment depends on intact F-actin polymerization and endosomal acidification, an important mechanism for endosomal protein sorting and trafficking.

Heparin binding protein (CAP37) is an opsonin for Staphylococcus aureus and increases phagocytosis in monocytes

Heparin binding protein (HBP), also known as cationic antibiotic protein (CAP37) or azurocidin, is stored in azurophilic granules of neutrophils and is released to the extracellular space when granulocytes phagocytose Staphylococcus aureus. We investigated whether extracellular HBP also has the potential to increase phagocytosis of S. aureus by other phagocytes. We used flow cytometry to characterize the binding of HBP to S. aureus and to simultaneously measure phagocytosis and superoxide production of opsonized S. aureus in monocytes and granulocytes. Our results demonstrate that HBP is a strong opsonin for S. aureus, and that monocytes, but not granulocytes, increase phagocytosis of HBP-treated S. aureus. However, HBP-treated S. aureus increases the production of superoxide in both monocytes and granulocytes as compared with untreated S. aureus. These findings support the role of granulocytes in the afferent limb of inflammation and demonstrate that HBP, when released from activated granulocytes, potentiates bacterial uptake in monocytes and enhances the potential of microbial killing in monocytes and granulocytes.

Heparin-binding protein (CAP37) is internalized in monocytes and increases LPS-induced monocyte activation

Previous studies have shown that the neutrophil-derived heparin-binding protein (HBP), also known as CAP37 or azurocidin, potentiates the LPS-induced release of proinflammatory cytokines (TNF-alpha, IL-1, and IL-6) from isolated human monocytes. To date, the mechanisms by which HBP enhances LPS-induced monocyte activation have not been elucidated, and it is not known whether HBP also increases the LPS-induced production of other bioactive substances. We studied human monocytes activated by recombinant human HBP and LPS and their interaction with the LPS receptor CD14. We hypothesized that the stimulatory effect of HBP on the LPS-induced release of proinflammatory mediators from monocytes was mediated by specific binding of HBP to monocytes, which resulted in an up-regulation of CD14. Our results demonstrated that HBP alone (10 microg/ml) stimulated the production of TNF-alpha from isolated monocytes. In addition, HBP had an additive effect on LPS-induced production of TNF-alpha and PGE2, suggesting a generalized monocyte activation. We used flow cytometry to demonstrate that HBP had a high affinity to monocytes but not to the LPS receptor CD14, and experiments performed at 4 degrees C indicated an energy-dependent step in this process. Confocal microscopy showed that monocytes internalize HBP within 30 min. These data suggest that mechanisms other than increased CD14 expression are responsible for the enhanced release of TNF-alpha or PGE2 in response to HBP and LPS.

Characterization of recombinant human HBP/CAP37/azurocidin, a pleiotropic mediator of inflammation-enhancing LPS-induced cytokine release from monocytes

Neutrophil-derived heparin-binding protein (HBP) is a strong chemoattractant for monocytes. We report here for the first time the expression of recombinant HBP. A baculovirus containing the human HBP cDNA mediated in insect cells the secretion of a 7-residue N-terminally extended HBP form (pro-HBP). Deletion of the pro-peptide-encoding cDNA sequence resulted in correctly processed HBP at the N-terminus. Electrospray mass spectrum analysis of recombinant HBP yielded a molecular weight of 27.237 +/- 3 amu. Consistent with this mass is a HBP form of 225 amino acids (mature part +3 amino acid C-terminal extension). The biological activity of recombinant HBP was confirmed by its chemotactic action towards monocytes. Furthermore, we have shown that recombinant HBP stimulates in a dose-dependent manner the lipopolysaccharide (LPS)-induced cytokine release from human monocytes.

Binding of bovine pancreatic trypsin inhibitor to heparin binding protein/CAP37/azurocidin. Interaction between a Kunitz-type inhibitor and a proteolytically inactive serine proteinase homologue

Heparin-binding protein (HBP; also known as CAP37 or azurocidin) is a member of the serine proteinase family. Evolution, however, has reverted this protein into a non-proteolytic form by mutation of two of the three residues of the active-site triad. Although proteolytically inactive, the human heparin-binding protein (hHBP) is still capable of binding bovine pancreatic trypsin inhibitor (BPTI). This was demonstrated by affinity chromatography to BPTI immobilized on a solid matrix and by studies on plasmin inhibition kinetics. hHBP competes with plasmin for BPTI and this effect on plasmin inhibition has been analyzed in terms of a kinetic model. A dissociation constant, Kd = 0.1 microM, was found for the interaction between BPTI and hHBP. The hHBP provides an example of a serine proteinase which has lost its catalytic function by reverting residues of the active center while still preserving its capability of specific interactions with Kunitz inhibitors. pHBP, the porcine counterpart to hHBP, on the other hand, was incapable of BPTI binding. The structural basis for the BPTI binding to the human protein and the species difference is discussed in terms of putative three-dimensional structures of the proteins derived by comparative molecular modelling methods.

Comparison of the effects of methoxysuccinyl-Ala-Ala-Pro-Val-chloromethyl ketone-inhibited neutrophil elastase with the effects of its naturally occurring mutationally inactivated homologue (HBP) on fibroblasts and monocytes in vitro

The mature neutrophils in the circulation contain, besides the different proteases known for a long time, a recently discovered proteolytically inactive elastase homologue (HBP/CAP37/azurocidin). This homologue, which we have named HBP due to its strong affinity to heparin, is a chemoattractant for monocytes and has been shown to induce reversible detachment and contraction when added to monolayers of endothelial cells or fibroblasts. HBP may therefore play a pivotal role in leukocyte migration in response to inflammation. In this report a comparison of CH3O-Suc-Ala-Ala-Pro-Val-CH2Cl-inhibited elastase with HBP, its naturally occurring homologue selectively mutated in active serine and histidine, reveals that homotypic aggregation of monocytes and contraction of fibroblasts is specific for HBP. HBP induces thrombospondin secretion from monocytes four times as efficiently as the inhibited elastase, and the same molecule was found unable to compete for a specific saturable binding of HBP to monocytes with an apparent KD of 3 x 10(-8)M.

A neutrophil-derived proteolytic inactive elastase homologue (hHBP) mediates reversible contraction of fibroblasts and endothelial cell monolayers and stimulates monocyte survival and thrombospondin secretion

Human heparin-binding protein (hHBP) is a recently discovered proteolytically inactive neutrophil elastase homologue with sequence identity to azurocidin and CAP37. The protein has antibacterial properties and chemotactic activity toward monocytes. In the present work, we show that monocytes, cultured under serum-free conditions, developed morphological changes and formed multicellular aggregates 4 h after the addition of hHBP at a concentration of 10 micrograms/ml. However, after prolonged incubation (11 days) with unchanged medium, the cells spread again. The hHBP-treated cells had a two- to threefold increase in survival compared to control cells, measured using trypan blue as an indicator of living cells. Differentiation of the alive cells to macrophages was detected by changes in morphology, a threefold increase in protein content, and a three- to fourfold increase in acid phosphatase activity. When monocytes in parallel experiments were labelled with [35S]methionine de novo synthesis and secretion of thrombospondin in a dose-dependent manner was observed after 16 h, with half-maximal secretion at 2 micrograms hHBP/ml and a maximal 12-fold increase in secretion with respect to controls at 16 micrograms/ml. Supplementary labeling with [35S]sulfate revealed that the same monocytes down-regulated the secretion of a large proteoglycan (300-400 kd), apparently also with a half-maximal decrease rate at 2 micrograms/ml hHBP. Exposure of confluent fibroblast and endothelial cell monolayers to hHBP (10 micrograms/ml) in the absence of fetal calf serum resulted in cell contraction leaving gaps between cells, the phenomenon being recognizable within 4 h after addition of hHBP. Addition of fetal calf serum to a concentration of 10% completely restored the monolayers. A unique role of hHBP in host defense involving recruitment of monocytes and a key function of hHBP in neutrophil extravasation in response to inflammatory chemotactic signals such as leukotriene B4, complement peptide C5a, and N-formyl-methionyl-leucyl-phenylalanine are suggested.

Covalent structure of two novel neutrophile leucocyte-derived proteins of porcine and human origin. Neutrophile elastase homologues with strong monocyte and fibroblast chemotactic activities

The covalent structures of two, novel, neutrophile, leucocyte-derived, strongly basic proteins of porcine and human origin have been determined by microsequencing in combination with time-of-flight plasma desorption mass spectrometry. The porcine protein primary structure of 219 amino acid residues was shown to contain 6 cysteine residues, 2 putative carbohydrate sites and 14% basic residues. The human protein contained 221 amino acid residues of which 8 were cysteine, 4 putative carbohydrate sites and 12% basic. A 47% direct sequence similarity to human neutrophile elastase was found, but due to mutations of two of the three amino acids in the catalytic triad, proteolytic activity is absent. Modelling and alignment studies unveil a close relationship of both proteins to the serine protease family, the greatest similarity being to those serine proteases present in granules from peripheral blood cells. Both proteins have been shown to be chemotactically active for monocytes and fibroblasts in vitro.

Platelet P1, P4-Di (adenosine-51) tetraphosphate (AP4A) in migraine patients before and during beta-adrenoceptor blockade

P1,P4-Di(adenosine-51) tetraphosphate (AP4A) is a metabolically inactive nucleotide which can be released from platelet dense granules. This study was designed firstly, to investigate whether platelet content of AP4A was decreased in patients with classical migraine and secondly, whether the content of AP4A was changed by beta-adrenoceptor blockade. No significant difference in platelet dense granule content of AP4A, was observed between 10 migraine patients and 10 normal controls. Both metoprolol, a beta 1-selective blocker and propranolol, a non-selective beta-blocker significantly decreased the migraine attack rate. However, while propranolol significantly reduced the platelet content of AP4A, metoprolol did not. Therefore, the present data suggest that platelet dense granule release, as estimated by the content of AP4A is not of major importance in migraine.

Diagnosis of storage pool deficiency by determination of diadenosine 5', 5'''-P1,P4-tetraphosphate in whole blood

Platelets from cat and cattle with Chediak-Higashi disease were found completely devoid of Ap4A as measured by high performance liquid chromatography. Using a very sensitive firefly biolumnescence method 6% of the normal content of Ap4A was, however, found in platelets from sick animals. A content of Ap A of 1.90 +/- 0.11 X 10 M (means +/- SEM, n = 10) was found in whole normal human blood as measured by firefly bioluminescense method in trichloroacetic acid extracts of the blood samples. This concentration corresponds to the contribution from the platelets, thus the contribution of Ap4A from erythrocytes and the "buffy-coat" is negligible. Using the same method an Ap4A contents in platelets of 0.063 and 0.021 nmol/mg of protein compared to the normal content of 0.42 nmol/mg of protein (1) was found in two patients with severe myeloproliferative disorder calculated in this way on basis of platelet counts and on the assumption that 10(11) platelets contain 189 mg of protein (2). Comparison of these figures with parallel HPLC analyses on acid extracts of platelets isolated from the same patient were in agreement. The storage pool deficiency of adenine nucleotides in this disease found by others on basis of release experiments (3) can thus be diagnosed by rapid and simple measurements of Ap4A in whole blood using the advantage of Ap4A being a specific components stored in dense granules.

On the mechanism of action of free purine bases on DNA synthesis in serum-starved L-cells treated with platelet extract

It has previously been found that there is a synergistic effect of free purine bases and low concentrations of dialyzed platelet extract on net synthesis of DNA in serum-starved fibroblast-like mouse L-cells. Experiments with a mutant line of L-cells that was deficient in hypoxanthine phosphoribosyl transferase (EC 2.4.2.8) indicated that purine bases had a stimulatory effect only if they were incorporated into cellular ribonucleotides. In the present paper it was shown that platelet extract induced the incorporation of hypoxanthine or adenine into both ATP and DNA. The induced net synthesis of DNA appears to take place in the nuclei and it requires that platelet extract is present in the medium only initially while free purine bases have to be present only later in the period of the experiment when DNA is being synthesized. The induction of both incorporation of free purine bases into DNA and ATP and of net DNA synthesis is dependent on heat-labile components in platelet extract. The extract cannot be substituted for by platelet derived growth factor.

Platelet-derived growth factor stimulates chemotaxis and nucleic acid synthesis in the protozoan Tetrahymena

Platelet-derived growth factor (PDGF) is in concentrations of a few nanograms per ml a very active chemoattractant for the free-living ciliated protozoan Tetrahymena; at the same time it induces a rapid increase in incorporation of radioactive nucleic acid precursors into RNA and DNA. We find it remarkable that this lower eukaryote responds to platelet-derived growth factor in very much the same way as fibroblastic cells.

Both hypoxanthine and adenosine stimulate DNA synthesis independently in serum-starved L cells treated with platelet protein

The effect of human platelet factors and purine derivatives on DNA synthesis has been investigated in mouse fibroblast-like L cells whose growth was arrested by serum starvation. When such cells were exposed to diluted platelet extract (e.g., 35 micrograms of protein per ml), a stimulatory effect on net DNA synthesis was observed. This effect was almost abolished by dialysis of the extract. The stimulation was, however, recovered by supplementing the diluted and dialyzed extract with hypoxanthine or adenosine. Similar phenomena were observed in pulse-labeling experiments performed with [3H]thymidine. In this case, however, there was a marginal stimulatory effect of adenosine or hypoxanthine alone. When the cells were treated with saturating concentrations of pure platelet-derived growth factor (PDGF), a stimulatory effect on pulse labeling was again obtained by the simultaneous presence of hypoxanthine or adenosine. In serum-starved cells of a mutant line of L cells deficient in hypoxanthine phosphoribosyltransferase, there was, however, no stimulatory effect on pulse labeling by hypoxanthine when it was added alone or together with either PDGF or diluted dialyzed platelet extract. It is suggested that the stimulation of DNA synthesis by the purine derivatives in the presence of a certain type of platelet proteins, probably involving PDGF, may be explained by their function as precursors for a purine ribonucleotide pool that is specifically related to DNA synthesis. Treatment of serum-starved L cells with high concentrations of dialyzed platelet extract (e.g., 240 micrograms of protein per ml) showed that platelets contain an additional type of factor that may substitute for the requirement of adenosine or hypoxanthine for DNA synthesis to take place. It is suggested that the effect of this type of factor may be to activate the catabolic activity of the purine salvage pathway.

Abundant amounts of diadenosine 5',5"'-P1,P4-tetraphosphate are present and releasable, but metabolically inactive, in human platelets

Diadenosine 5',5"'-P1,P4-tetraphosphate (Ap4A) may be formed in the back reaction of the amino acid-activation reaction [Zamecnik, Stephenson, Janeway & Randerath (1966) Biochem. Biophys. Res. Commun. 24, 91-98]. On the basis of a number of observations of the properties of Ap4A it has been suggested that it may have a signal function for the initiation of DNA replication in eukaryotic cells] Grummt (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 371-375]. In the present paper human platelets have been shown to contain relatively large amounts of Ap4A. The compound is apparently metabolic inactive in platelets, but it is almost quantitatively released when platelets are activated to aggregate by treatment with thrombin. The results are discussed in connection with the known growth-stimulating activity of platelets.

Studies on a Ca2+-dependent nucleoside triphosphate pyrophosphohydrolase in rat liver plasma membranes

A membrane-bound Ca2+-dependent nucleoside triphosphate pyrophosphohydrolase was solubilized in deoxycholate, separated from inorganic pyrophosphatase, and partially characterized. The Km for a variety of substrates was determined. At 10(-4) M free Ca2+ (pH 8.0) the Km values for ATP and GTP were 0.32 and 2.2 microM, respectively. With ATP as substrate, Mg2+, Sr2+, and Ba2+ could only replace Ca2+ to a limited degree. Both purine and pyrimidine nucleoside triphosphates were hydrolyzed yielding PPi and mononucleotides and similarly AMP and formed from adenosine-(beta gamma-methylene)triphosphate. UDPglucose was hydrolyzed at the pyrophosphate bond. Tripolyphosphate and phosphoribosyl-1-pyrophosphate (P-rib-PP) were not hydrolyzed. Substrate competition experiments showed that GTP inhibited pyrophosphohydrolysis of ATP competitively. However, UDP glucase and adenosine-(beta gamma-methylene)triphosphate inhibited ATP pyrophosphohydrolysis in a non-linear manner. Adenosine-(beta gamma-methylene)triphosphate inhibited pyrophosphohydrolysis of UDPglucose non-competitively, whereas UDPglucose inhibition of adenosine-(beta gamma-methylene) triphosphate pyrophosphohydr-lysis was competitive. The molecular weight of ATP pyrophosphohydrolase was estimated at 120 000 and the pI at 5.1 Pyrophosphohydrolysis of adenosine-(beta gamma-methylene)triphosphate was studied in a number of rat organs. Nearly all activity could be sedimented at 50 000 X g. Very high activities were found in liver, kidney and small intestine, whereas low activities were found in brain and blood.

A calcium ion-dependent adenosine triphosphate pyrophosphohydrolase in plasma membrane from rat liver. Demonstration that the adenosine triphosphate analogues adenosine 5'-[betagamma-imido]triphosphate and adenosine 5'-[betagamma-methylene]-triphosphate are substrates for the enzyme

An ATP pyrophosphohydrolase in a rat liver plasma-membrane subfraction was studied with respect to specific Ca2+ activation of the beta-phosphate bond hydrolysis. ATP and, in addition, adenosine 5'-[betagamma-imido]triphosphate and adenosine 5'-[betagamma-methlylene]triphosphate were substrates for Ca2+-stimulated enzymic hydrolysis of the beta-phosphate bond. A 15-fold activation was observed by raising the free Ca2+ concentration from 10(-7) to 10(-5) M. Mg2+ had little effect. Solubilization in 1% deoxycholate and partial purification on a sucrose density gradient resulted in a 5-fold increase in specific activity with unaltered Ca2+-stimulation pattern. The possible importance of the enzyme in Ca2+ transport is discussed.

Adult hypophosphatasia

A case of adult hypophosphatasia under treatment with a high orthophosphate (P1) intake is described. The patient is a 53-year-old woman. Her symptoms have progressed for seven years, and it has been necessary to perform osteosynthesis of both crura. The diagnosis rests upon a characteristic clinical picture, low serum alkaline phosphatase activity, high urinary excretion of phosphoethanolamine, and an invariably elevated concentration of inorganic pyrophosphate (PP1) in plasma accompanied by a very high excretion of this compound in the urine. An improved technique allowed specific determinations of microquantities of PP1 in biologic materials. The concentrations of PP1 in the plasma and urine remained unchanged when the patient's intake of phosphorus was increased to 1.98 g/day. The PP1/P1 ratio in the urine was 10-20 before treatment. During treatment P1 excretion increased. PP1 excretion did not change, and the ratio decreased to around 7. The renal tubular transport of PP1 probably was saturated, and therefore PP1, which was circulating in abnormally high concentrations in the patient's fluids, could not be removed by loading with P1. Four months of treatment did not benefit the patient.