Reaction mechanism of electron transfer from FeII(CN)6(4-) or W(IV)(CN)8(4-) to the cupric ions in human copper, zinc superoxide dismutase

The electron transfer reactions from FeII(CN)6(4-) and W(IV)(CN)8(4-) to the cupric ions in human copper, zinc superoxide dismutase were followed by the micro-stopped-flow method. The kinetic rate data clearly indicate that FeII(CN)6(4-) or W(IV)(CN)8(4-) first forms an adduct with the enzyme through the interaction with Arg143 of the active cavity and then an electron from FeII(CN)6(4-) or W(IV)(CN)8(4-) of the adduct transfers to the cupric ion in the enzyme. The dissociation constants of the adducts of FeII(CN)6(4-) and W(IV)(CN)8(4-) were 4.0(+/-0.3) x 10(-3) and 2.2(+/-0.3) x 10(-3) M, respectively. In spite of the difference between the standard redox potentials of FeIII(CN)6(3-)/FeII(CN)6(4-) (468 mV) and W(V)(CN)8(3-)/W(IV)(CN)8(4-) (556 mV), the electron transfer rate constant (0.148(+/-0.005) s(-1) of FeII(CN)6(4-) at 25 degrees C is very similar to that of W(IV)(CN)8(4-) (0.072(+/-0.011) s(-1)). The entropy values of the adduct formations and the activation energies of the electron transfer rates were determined by the temperature dependence of the dissociation constants of the adducts and the electron transfer rates. The enthalpy values of the formation of adducts are almost zero, so that the driving forces to form the adducts are mainly derived from the entropy. The activation energy of the electron transfer rate of FeII(CN)6(4-) is very similar to that of W(IV)(CN)8(4-). The formation of the adduct between FeII(CN)6(4-) and the enzyme was inhibited by the presence of various anions (ClO4-, SO4(2-), SCN-, and N3-). The bulky anions SO4(2-) and ClO4- behave as competitive inhibitors for FeII(CN)6(4-); these anions should interact mainly with Arg143, as it has a positive charge at the entrance of the active cavity. The competitive inhibition constants of ClO4-, SO4(2-), and SCN- were 0.010, 0.012, and 0.008 M. The azide ion, which is smaller than SO4(2-) or ClO4-, shows mixed inhibition, because N3- can interact with Arg143 (competitive inhibition) and also directly binds to the cupric ion in h-SOD (noncompetitive inhibition). The competitive and noncompetitive inhibition constants of N3- were 0.004 and 0.016 M, respectively.

Binding of a large chondroitin sulfate/dermatan sulfate proteoglycan, versican, to L-selectin, P-selectin, and CD44

Here we show that a large chondroitin sulfate proteoglycan, versican, derived from a renal adenocarcinoma cell line ACHN, binds L-selectin, P-selectin, and CD44. The binding was mediated by the interaction of the chondroitin sulfate (CS) chain of versican with the carbohydrate-binding domain of L- and P-selectin and CD44. The binding of versican to L- and P-selectin was inhibited by CS B, CS E, and heparan sulfate (HS) but not by any other glycosaminoglycans tested. On the other hand, the binding to CD44 was inhibited by hyaluronic acid, chondroitin (CH), CS A, CS B, CS C, CS D, and CS E but not by HS or keratan sulfate. A cross-blocking study indicated that L- and P-selectin recognize close or overlapping sites on versican, whereas CD44 recognizes separate sites. We also show that soluble L- and P-selectin directly bind to immobilized CS B, CS E, and HS and that soluble CD44 directly binds to immobilized hyaluronic acid, CH, and all the CS chains examined. Consistent with these results, structural analysis showed that versican is modified with at least CS B and CS C. Thus, proteoglycans sufficiently modified with the appropriate glycosaminoglycans should be able to bind L-selectin, P-selectin, and/or CD44.

Screening for Drosophila proteins with distinct expression patterns during development by use of monoclonal antibodies

Kc 167 is a cell line established from Drosophila embryonic hemocytes and has been shown to express many extracellular matrix (ECM) and other proteins important during development. We have screened monoclonal antibodies (mAbs) raised against heparin affinity purified proteins from conditioned medium of Kc 167 cells to identify novel proteins with important roles for development. One mAb recognized a protein expressed with temporary and tissue specific patterns during Drosophila embryogenesis and larval development. This approach is an alternative to screening of Expression Sequence Tag (EST) clones by in situ hybridization to initiate reverse genetics. In addition, a number of mAbs recognizing ECM proteins were also identified. These mAbs will be useful for biochemical and cell biological analyses of Drosophila ECM proteins.

The HELLGH motif of rat liver dipeptidyl peptidase III is involved in zinc coordination and the catalytic activity of the enzyme

The role of the HELLGH (residues 450-455) motif in the sequence of rat dipeptidyl peptidase III (EC 3.4.14.4) was investigated by replacing Glu451 with an alanine or an aspartic acid residue and by replacing His450 and His455 with a tyrosine residue by site-directed mutagenesis. Mutated cDNAs were expressed three or four times in Escherichia coli, and the resulting proteins were purified to apparent homogeneity. None of the expressed mutated proteins exhibited DPP III activity. The mutants of Glu451 contained 1 mol of zinc per mole of protein, but mutants His450 and His455 did not contain significant amounts of zinc as determined by atomic absorption spectrometry. The Leu453-deleted enzyme (having the zinc aminopeptidase motif HExxH-18-E) had almost the same order of binding affinity (for Arg-Arg-2-naphthylamide) as the wild-type enzyme, but the specificity constant was about 10%. These results provide evidence that the suitable number of amino acids included between Glu451 and His455 is three residues for the enzyme activity and confirm that residues His450, His455, and Glu451 are involved in zinc coordination and catalytic activity.

Aminopeptidase B is structurally related to leukotriene-A4 hydrolase but is not a bifunctional enzyme with epoxide hydrolase activity

Aminopeptidase B (Ap B; EC 3.4.11.6) is a zinc-binding protein that contains the consensus sequence HEXXHX18E (324-347), conserved among the M1 family of metallopeptidases. To determine if these putative zinc-binding residues (His324, His328 and Glu347) and the active-site Glu325 are essential for the enzyme activity, we replaced the histidines with tyrosines and the glutamic acid residues with alanines using site-directed mutagenesis. The cDNAs were expressed in Escherichia coli, and the resulting recombinant proteins, named H324Y, E325A, H328Y and E347A, were purified to apparent homogeneity. None of the expressed mutated proteins showed aminopeptidase activity. The E325A enzyme contained 1 mol of zinc per mol of protein, and the other three mutants, H324Y, H328Y and E347A, did not contain significant amounts of zinc, as determined by atomic absorption spectrometry. From sequence-homology searches, Ap B is known to be closely related to leukotriene (LT)-A4 hydrolase (EC 3.3.2.6). We examined human placental Ap B and recombinant rat Ap B, both of which had been purified previously [Fukasawa, Fukasawa, Kanai, Fujii and Harada (1996) J. Biol. Chem. 271, 30731-30735], to determine whether or not they had epoxide hydrolase activities. However, neither enzyme hydrolysed LTA4 into LTB4. We then replaced some amino acids in the domain of the rat enzyme similar to the LTA4-binding site of LTA4 hydrolase. However, these mutants, Y408F, N409S and NE409-410SS also did not possess any epoxide hydrolase activity. We concluded that Ap B is an M1-family zinc metallopeptidase without epoxide hydrolase activity.

Reduced reperfusion injury in muscle. A comparison of the timing of EPC-K1 administration in rats

EPC-K1, a phosphate diester of alpha-tocopherol and ascorbic acid, is a new hydroxyl radical scavenger. We examined the effects of EPC-K1 according to differences in the timing of its administration. Warm ischemia, produced by vascular pedicle clamping, was sustained for 4 hours. After 24 hours of reperfusion, muscle injury was evaluated in 4 groups: the first group received a sham operation, the second group was treated with an intravenous injection of EPC-K1 prior to ischemia, the third group was treated with EPC-K1 prior to reperfusion, and the fourth group was controls. Compared with the control group, both the preischemic and pre-reperfusion EPC-K1-treated groups showed a statistically significant amelioration in the reduction of isometric muscle contraction. There were also significant reductions in the muscle and serum levels of thiobarbituric acid reactive substances (TBA-RS) and muscle damage, indicated by the biochemical and histological study. A comparison of the timing of EPC-K1 administration revealed that only the muscle TBA-RS level in the pre-reperfusion EPC-K1-treated group was significantly higher than that in the preischemic EPC-K1-treated group. These observations indicate that EPC-K1 not only by preischemic but also by pre-reperfusion administration acted effectively on reperfusion injury in muscle, thereby improving muscle function.

Identification and characterization of ligands for L-selectin in the kidney. I. Versican, a large chondroitin sulfate proteoglycan, is a ligand for L-selectin

Ligands for a leukocyte adhesion molecule, L-selectin, are expressed not only in the specific vascular endothelium in lymph nodes and Peyer's patches but also in the extravascular tissues such as the brain white matter, choroid plexus and the kidney distal straight tubuli. However, the biological significance of these extravascular ligands is currently unknown. We now report the purification and characterization of a novel extravascular ligand for L-selectin in the kidney using a tubule-derived cell line, ACHN. Binding of L-selectin-IgG chimera (LEC-IgG) to the isolated ligand was specifically blocked with either (i) anti-L-selectin mAb, (ii) EDTA, (iii) fucoidan, (iv) chondroitin sulfate (CS) B or CS E, or (v) treatment with chondroitinases. Partial amino acid sequencing, Western blotting and immunoprecipitation analyses showed that a major ligand for L-selectin in ACHN cells is versican of 1600 kDa. Histochemical as well as biochemical analyses verified that a versican subspecies in the kidney was indeed reactive with L-selectin. Studies with cell lines including those derived from the kidney indicated that a certain glycoform and/or splice form of versican is reactive with L-selectin. Under pathological conditions such as those induced by unilateral ureteral obstruction, versican was shed from the distal straight tubuli and became localized in the adjacent vascular bundles around which a substantial leukocyte infiltration was concomitantly observed. Possible involvement of versican in leukocyte trafficking into the kidney under diseased conditions is discussed.

Vascular and non-vascular ligands for L-selectin

Ligands for L-selectin are expressed not only on vascular endothelial cells but also in the extravascular tissues. In this article, we summarize the current understanding of the "vascular" ligands for L-selectin. We also describe identification of "non-vascular" ligands for L-selectin and discuss their possible biological significance.

Human neutrophil elastase degrades inter-alpha-trypsin inhibitor to liberate urinary trypsin inhibitor related proteins

Urinary trypsin inhibitor (UTI) is a physiological protease inhibitor and inter-alpha-trypsin inhibitor (ITI) is regarded as a precursor of UTI. The purpose of this study is to determine the mechanism of the UTI release from ITI. To examine this, ITI was digested by human neutrophil elastase at various concentrations, and UTI-related proteins which were of the same size as UTI were obtained. The amino acid sequence of the 15 amino acid residues at the N-terminal of UTI-related proteins, corresponded to that of UTI. The amino acid sequences of the small amount of peptides detected corresponded to those of peptides from the heavy chain1 (H1) and the heavy chain2 (H2) of ITI, suggesting that most UTI-related proteins do not combine with peptides from the H1 and H2 of ITI. It was also revealed that UTI-related proteins have several physiological activities similar to those of UTI, i.e., human trypsin inhibitory activity, human neutrophil elastase inhibitory activity, inhibition of tumor necrosis factor-alpha (TNF-alpha) production from rat macrophages and of superoxide production from rabbit leukocytes. These results demonstrated that ITI is a precursor of UTI which is digested by human neutrophil elastase to release UTI, and that its elastase inhibitory activity is derived from UTI.

Dipeptidyl peptidase III is a zinc metallo-exopeptidase. Molecular cloning and expression

We have purified dipeptidyl peptidase III (EC 3.4.14.4) from human placenta. It had a pH optimum of 8.8 and readily hydrolysed Arg-Arg-beta-naphthylamide. Monoamino acid-, Gly-Phe-, Gly-Pro- and Bz-Arg-beta-naphthylamides were not hydrolysed at all. The enzyme was inhibited by p-chloromercuriphenylsulphonic acid, metal chelators and 3,4-dichloroisocoumarin and contained 1 mol of zinc per mol of enzyme. The zinc dissociation constant was 250 fM at pH 7. 4 as determined by the zinc binding study. We isolated, by immunological screening of a Uni-ZAP XR cDNA library constructed from rat liver mRNA species, a cDNA clone with 2633 bp encoding the rat enzyme. The longest open reading frame encodes a 827-residue protein with a theoretical molecular mass of 92790 Da. Escherichia coli SOLR cells were infected with the pBluescript phagemid containing the cloned cDNA and established the overexpression of a protein that hydrolysed Arg-Arg-beta-naphthylamide. The recombinant protein was purified and the amino acid sequence of the protein was confirmed. We presumed that the putative zinc-binding domain involved in catalysis was present in the recombinant enzyme. It was a novel zinc-binding motif in that one amino acid residue was inserted into the conserved HEXXH motif characteristic of the metalloproteinases.

The pH dependent properties of metallotransferrins: a comparative study

The dependence on pH of the absorption and circular dichroic spectra of iron(III), cobalt(III) and copper(II) transferrins has been (re)investigated. In the alkaline region, the CD profiles of iron(III) and cobalt(III) transferrin are essentially pH independent up to pH 11; only for very high pH values (pH > 11) is breakdown of the cobalt(III) and iron(III) transferrin derivatives observed, without evidence of conformational rearrangements. By contrast, the CD profiles of copper transferrin show drastic changes in shape around pH 10; these spectral changes, which are fitted to a pKa of approximately 10.4, are interpreted in terms of a substantial rearrangement of the local environment of the copper ions at high pH. Although the CD spectra of copper transferrin at alkaline pH strictly resemble those observed upon addition of modifier anions, the mechanism of site destabilization in the two cases is different; at variance with the case of modifier anions, our results suggest that the high pH form of copper transferrin still contains the synergistic anion. A 13C NMR experiment has confirmed this view. In the acidic region, iron(III) and cobalt(III) transferrins are stable down to pH approximately 6. For lower pH values progressive metal detachment is observed without evidence of conformational changes; around pH 4.5 most bound metals are released. In the case of the less stable copper-transferrin, metal removal from the specific binding sites is already complete around pH 6.0; in concomitance with release from the primary sites, binding of copper ions to secondary sites is observed. Additional information has been gained from CD experiments in the far UV. The pH dependent properties of iron(III), cobalt(III) and copper(II) transferrin are discussed in the frame of the present knowledge of transferrin chemistry, particular emphasis being attributed to the comparison between tripositive and bipositive metal derivatives.

Reduced ischemia-reperfusion injury in muscle. Experiments in rats with EPC-K1, a new radical scavenger

L-ascorbic acid 2-[3,4-dihydro-2,5,7,8-tetramethyl- 2-(4,8,12-trimethyltridecyl)-2H-1-benzopyran-6-yl hydrogen phosphate] potassium salt (EPC-K1), a phosphate diester of alpha-tocopherol and ascorbic acid, is a potent antioxidant. We examined the effects of EPC-K1 on ischemia-reperfusion injury in the skeletal muscle of rats, using an ischemic revascularized hind limb model. Warm ischemia (25 degrees C), produced by vascular pedicle clamping, was sustained for 4 hours. After 24 hours of reperfusion, skeletal muscle injury was evaluated in 2 groups: one group treated by intravenous injection of EPC-K1 (10 mg/kg) prior to ischemia, and a group of controls. The EPC-K1-treated group showed a statistically significant amelioration in the reduction of the isometric muscle contraction, inhibition of the elevation of the muscle wet- to dry-weight ratio, limitation of the muscle level of thiobarbituric acid reactive substances and the serum levels of creatine phosphokinase, lactate dehydrogenase and mitochondrial glutamic oxaloacetic transaminase, and reduction of the extent of muscle injury according to the histological findings. These observations indicate that EPC-K1 acted effectively on ischemia-reperfusion injury in the rat skeletal muscle and thereby improved muscle function.

Characterization of monoclonal antibodies against (1R,2R)-cyclohexanediamine platinum(II)-DNA adduct

Two monoclonal antibodies raised against Pt(II)(1R,2R-cyclohexanediamine)-DNA were prepared, and the specificity of the monoclonal antibodies against Pt(II)(cyclohexanediamine)-DNA derivatives was determined by competitive enzyme-linked immunosorbent assay. The binding affinity of the monoclonal antibodies is apparently influenced by the cyclohexanediamine moiety of Pt(II)(cyclohexanediamine)-DNA adducts, but the monoclonal antibodies can not bind to the low molecular analogue, Pt(II)(1R,2R-cyclohexanediamine)-d(GpG), which is the intrastrand binding model compound of Pt(II)(1R,2R-cyclohexanediamine)-DNA. Therefore, the monoclonal antibodies recognize the macromolecular parts, including DNA duplex, in addition to the cyclohexane moieties of the platinum complexes on Pt(II)(cyclohexanediamine)-DNA adducts.

Copper binding selectivity of N- and C-sites in serum (human)- and ovo-transferrin

Copper binding selectivity of the N- and C-sites in serum (human)- and ovo-transferrin was investigated through copper binding constants, copper dissociation rate constants, and EPR spectra. At pH 7.4, stepwise copper binding constants of serum (human)-transferrin were K1 = 1.8 (+/- 0.6) x 10(12) M-1 and K2 = 1.2 (+/- 0.5) x 10(11) M-1, and those of ovo-transferrin were K1 = 1.9 (+/- 0.5) x 10(11) M-1 and K2 = 2.1 (+/- 0.4) x 10(11) M-1. Absorbance changes resulting from copper binding to the C- or N-site at various ratios of Cu2+/apo-transferrin were separated by a kinetic method. It was clearly indicated that, in serum (human)-transferrin, the copper binding affinity for the C-site was much larger than that for the N-site, whereas in ovo-transferrin, the C- and N-sites have almost the same affinity for copper ions. In the presence of anions (0.1 M KCl or 0.1 M NaClO4), the stepwise copper binding constants of serum (human)-transferrin were almost 10-times smaller than those in the absence of the anions. The selectivity in binding the copper ions to both sites of serum (human)-transferrin in the presence of 0.1 M NaClO4 is much smaller than that in the presence of 0.1 M KCl or in the absence of the anions (0.1 M KCl and 0.1 M NaClO4). EPR spectra of the copper ions of the N-site in dicupric serum-transferrin are dramatically changed respectively by the addition of 0.1 M KCl, 0.1 M NaCl, and 0.1 M NaClO4. This suggests that the change in the coordination geometry of the copper ions occurs at the N-site.

Novel beta-D-galactofuranose-containing high-mannose type oligosaccharides in ascorbate oxidase from Acremonium sp. HI-25

Ascorbate oxidase from the fungus Acremonium sp. HI-25 is a copper-containing glycoprotein that catalyzes the oxidation of ascorbic acid to dehydroascorbic acid. Monosaccharide composition analysis showed that the enzyme contains exclusively N-linked oligosaccharide chains. Following liberation by hydrazinolysis/re-N-acetylation, and fractionation by HPLC on anion exchange. Amide-80 and/or octadecyl silica columns after derivatization with p-aminobenzoic ethyl ester, the structures of the twelve major neutral oligosaccharides were identified by FAB-MS, 400 MHz 1H-NMR, methylation analysis, mild acid hydrolysis, and/or sequential exoglycosidase digestions. Acremonium sp. ascorbate oxidase was found to consist of high-mannose type oligosaccharides (76.3%) having 4 to 9 mannose residues and a series of novel D-galactofuranose-containing high-mannose type oligosaccharides (18.6%) with the following structure.

Improvement of insulin sensitivity and dyslipidemia with a new alpha-glucosidase inhibitor, voglibose, in nondiabetic hyperinsulinemic subjects

This study was undertaken to investigate the effect of voglibose, a new alpha-glucosidase inhibitor, on glucose and lipid metabolism in nondiabetic hyperinsulinemic subjects. Sixteen nondiabetic subjects with hyperinsulinemia participated in the study. They were divided into two groups of eight subjects with normal (NGT) and impaired (IGT) glucose tolerance. A meal tolerance test and a 75-g oral glucose tolerance test (OGTT) were performed at the beginning (baseline phase) and end (treatment phase) of the 12-week treatment. Serum lipid levels were measured every 4 weeks throughout the treatment phase and follow-up phase (8 weeks). All patients received 1 0.2-mg tablet of voglibose before each test meal (3 tablets per day). We also measured insulin sensitivity using a steady-state plasma glucose (SSPG) method in eight normotensive hyperinsulinemic subjects and in eight age- and body mass index (BMI)-matched control subjects before and after the drug treatment. Voglibose significantly decreased the responses of plasma glucose and insulin on the meal tolerance test. The area under the curve for 2-hour insulin during the 75-g OGTT decreased after treatment, whereas that for 2-hour glucose did not change before and after treatment. SSPG was reduced after treatment, indicating improvement of insulin sensitivity. Moreover, treatment with voglibose resulted in a significant decline of triglyceride level and an elevation of high-density lipoprotein (HDL) cholesterol and apolipoprotein A-1. These values returned to near-baseline levels after the drug was discontinued. Consequently, we conclude that this agent not only has a direct hypoglycemic effect through decreased absorption of carbohydrate, but also a hypoinsulinemic and hypolipidemic effect via improved insulin sensitivity.

Modified method using a somatostatin analogue, octreotide acetate (Sandostatin) to assess in vivo insulin sensitivity

In order to evaluate the steady state plasma glucose (SSPG) method by using a new somatostatin derivative, octreotide acetate (Sandostatin) instead of somatostatin that we had used for the insulin sensitivity test, we examined whether octreotide was able to suppress C-peptide (CPR), glucagon (IRG), and GH to a similar degree to that achieved with somatostatin. A total of 52 studies were performed in 45 essential hypertensive subjects and 7 healthy subjects. Octreotide was given subcutaneously in a does of 50 micrograms or 100 micrograms 10 min before the test (sc 50, sc 100 groups) or intravenously infused over 2 h (10 micrograms in bolus followed by a constant infusion, 50, 100, or 150 micrograms/2 h: i.v. 50, i.v. 100, i.v. 150 groups). In all of the groups the plasma immunoreactive insulin (IRI) concentration increased gradually after insulin injection and reached the steady state plasma insulin (SSPI) level between 40 and 60 microU/ml at 60 min through 120 min. Plasma CPR at 120 min was the most suppressed (by 67% of the basal level in i.v. 150 group during the study period), but on the other hand in both the sc 100 and i.v. 100 groups the plasma CPR concentration at 120 min was suppressed by nearly 40%, but not significantly suppressed in either the sc 50 or the i.v. 50 group. Plasma IRG and GH were strongly suppressed after 60 min in all groups during the study period. Plasma glucose had increased significantly at 30 min and reached the steady state at 90 min through 120 min in hypertensive and healthy subjects. The results indicated that the modified SSPG method with continuous intravenous infusion of Octreotide at 150 micrograms/2 h was adequate for the measurement of insulin sensitivity.

Cardioscopic spectrum of the left ventricular endocardial surface and its relation to histologic changes in idiopathic myocarditis

To examine feasibility of percutaneous cardioscopy for diagnosis of idiopathic myocarditis, cardioscopic appearance of the left ventricle and biopsy findings were compared in 21 such patients. The endocardial surface was milky white, red, pink, or reddish brown and edematous at the segments that exhibited histologic changes of acute myocarditis; purplish red in those that exhibited chronic active myocarditis; and yellow in those that exhibited chronic inactive or healed myocarditis. Follow-up study by repeated cardioscopy and biopsy in six patients revealed that the milky white surface disappeared and that the red, pink, and reddish brown surfaces changed to purplish red and then to yellow or white. The results indicate that the endocardial coloration of the left ventricle represents histologic changes and that cardioscopy is feasible for macroscopic pathologic diagnosis and for follow-up of idiopathic myocarditis.