Stability Of Coil Research Articles

Analysis on the cryogenic stability and mechanical properties of the LHD helical coils

Transient normal-transitions have been observed in the superconducting helical coils of LHD. Propagation of a normal-zone is analyzed with a numerical simulation code that deals with the magnetic diffusion process in a pure aluminum stabilizer. During excitation tests, a number of spike signals are observed in the balance voltage of the helical coils, which seem to be caused by mechanical disturbances. The spike signals are analyzed by applying pulse height analysis and the mechanical properties of the coil windings are investigated.

Thermodynamic model for the stabilization of trigonal thiolato mercury(II) in designed three-stranded coiled coils.

A thermodynamic model is presented that describes the binding of Hg(II) to de novo designed peptides, Tri L9C and Baby L9C, which were derived from the Tri family. The Tri peptides are based on the parent sequence Ac-NH-G(LKALEEK)(x)()G-CONH(2) and are known to form two-stranded coiled coils at low pH (pH <4) and three-stranded coiled coils at high pH (pH >7). Tri L9C (x = 4) contains a four heptad repeat sequence with cysteine in position 9 and leucines in the other a and d positions; Baby L9C (x = 3), which also has a cysteine in position 9 but is one heptad shorter than Tri L9C, was designed to form less stable helical coiled coils in solution. The free energies of coiled coil formation for Tri, Tri L9C, Baby Tri, and Baby L9C at pH 2.5 and 8.5 were determined by guanidinium denaturation titrations; Tri L9C was observed to be highly helical in the absence of denaturant at pH 8.5 while Baby L9C contained <20% helical content at pH 8.5, indicating a weakly associated or unassociated coiled coil. Size-exclusion chromatography (SEC) verified that Baby L9C was a monomer at pH 8.5. The helicity of Baby L9C was induced by addition of HgCl(2). The subsequent formation of a trigonal thiolato Hg(II) in the interior of a three-stranded coiled coil was verified by the presence of a characteristic HgS(3) UV band at 248 nm. Titrations of Tri L9C and Baby L9C into solutions of HgCl(2) at pH values between 7 and 9 were performed to extract binding constants. Global fits to the data employed a mechanism that involved initial binding of mercury to the peptides forming a two-stranded coiled coil with linear thiolato Hg(II) at [peptide]/[Hg] <2, followed by addition of a more weakly associated third helix to generate a three-stranded coiled coil. This mechanism would require the deprotonation of the third cysteine thiol to generate the trigonal thiolato Hg(II) at pH >7.5 [the pK(a) of the cysteine thiol in the presence of Hg(II)]. Support for this mechanism was given by the observation of a three-stranded coiled coil by SEC in a solution of Tri L9C at pH 7.0.

New Embolization Coil Containing a Nitinol Wire Core: Preliminary In Vitro and In Vivo Experiences

To improve the stability of the standard stainless steel embolization coil by adding a nitinol wire core. With use of one coil with a nitinol wire core and one without one, stability and resistance to elongation were measured in vitro. Thirty-one factory-made stainless-steel macrocoils equipped with preshaped nitinol wire cores were acutely deployed into branches of the superior mesenteric artery (SMA) in five pigs (part I of the study). Fifteen homemade retrievable coils with thermal shape memory (TSM) nitinol wire cores were acutely deployed in the abdominal aortae or inferior venae cavae of four pigs (part II). Coils with a superelastic (SE) nitinol wire core (n = 9), a TSM nitinel wire core (n = 5), and without a core (n = 5) were compared in carotid embolization (part III). In vitro, the expansile strength of the reinforced coils was significantly greater and elongation was significantly less than the standard coils (P <.01). In part I, coils were easily deployed via diagnostic catheters. In part II, ability to reposition the coils facilitated optimal coil configuration, which resulted in effective self-anchoring and occlusion. In part III, no coils with a SE core migrated, whereas one of five with a TSM core and three of five without reinforcement migrated immediately. The core significantly increased coil stability and postplacement configuration (P <.01). Addition of a nitinol wire core increases the intravascular stability of the standard embolization coil by significantly enhancing expansile force and postplacement configuration. The wire core does not adversely affect the handling of the coil. The ability to reposition/retrieve the coil is a desirable feature.

Excitation properties and cryogenic stability of helical coils for the LHD

The helical coils for the Large Helical Device are the world's largest pool-cooled superconducting coils in operation. These were expected to be cryostable up to 13.0 kA at 4.4 K on a basis of the measured recovery currents in all the short samples. However, a normal-zone was induced at higher than 11 kA repeatedly. It propagated to the finite length and recovered within several seconds except at 11.45 kA. Because of slow current diffusion into a pure aluminum stabilizer, a normal zone can propagate dynamically below the cold-end recovery current. The excitation tests have been carried out, and average 11.65 kA has been achieved by grading the current in the three blocks of the helical coil. The disturbance during excitations and the cryogenic stability of the coil are presented.

Shape memory alloy coils optimized for electrical connectors

In an effort to reduce costs associated with automotive electrical connectors, auto manufacturers have looked to tin-coated terminals as an effective alternative to more expensive gold-coated terminals. Tin, however, is highly subject to a wear phenomenon known as fretting corrosion, which increases the contact resistance and renders the terminals useless. One solution to minimize fretting corrosion is to increase the terminal normal force. In ordinary electrical terminals, an increased normal force leads to other problems such as high insertion and removal forces. This work is a continuation of previous research in which a Ni-Ti shape memory alloy (SMA) coil was developed in order to increase the high temperature normal force of tin-coated terminals while maintaining moderate room temperature insertion forces. In particular, this work addresses the cyclic stability of the SMA coil when subjected to repeated temperature cycles over extended periods, the maximization of normal force provided by the coil for the amount of SMA used, and the long-term high-temperature performance of the SMA. This research has resulted in the reduction of the SMA wire diameter by nearly 30%, an increase in high temperature removal force of the terminal from approximately 20 N without the SMA to 60 N with it, and an associated reduction in cost by nearly 50% over the previous design. To accomplish these improvements, the SMA composition was changed from 55.1 wt% Ni to 49.7 wt% Ni, and the optimum training temperature for the new composition was found to be 400/spl deg/C.

極低温用負膨張コイルボビンの開発 高強度ポリエチレン繊維／アルミナ繊維系混合強化複合材料からなるパイプの弾性率及び熱歪特性

Hybrid composite pipes reinforced with high-strength polyethylene fiber (DF) and alumina fiber (AlF) were prepared to develop the coil bobbin for stable superconducting coils. The bobbin in which the circumferential thermal strain expands with cooling and in which the circumferential Young's modulus is large would be effective for stable coils. The unidirectional hybrid composite (ADFRP) showed 0 thermal expansion coefficient when the ratio between DF and AIF volume was 5/5 in fiber direction, and its Young's modulus was larger than that of DF reinforced plastic (DFRP) both in parallel and perpendicular to fiber direction. The circumferential and longitudinal Young's moduli of ADFRP pipe were larger than those of DFRP pipe. The average value of inner and outer circumferential thermal strains with cooling down showed 0 with a filament winding (FW) angle of 90deg when the ratio between DF and AIF volume (D/A) was 5/5. When D/A equals 5/5, the calculated thermal strain with cooling of the pipe showed good agreement with the average of observed inner and outer thermal strains. The circumferential thermal strain showed an expansion with a FW angle of 50-90deg, and an absolute value was smaller than those of DFRP. The inner and outer circumferential thermal strains were different. The difference decreased with an increase of the ratio inner diameter/thickness, and the differences were smaller than those of DFRP with a decrease of the degree of anisotropy of thermal expansion coefficients in UD-FRP. The experimental data were obtained to make it possible to devise a coil bobbin with negative thermal expansion coefficient by ADFRP.

Coil embolization of a false aneurysm with aorto-cutaneous fistula after prosthetic graft replacement of the ascending aorta

Aim: To report palliative embolization of a false aneurysm over the distal suture line of an ascending aorta graft replacement. Material and Method: A 78-year-old male patient was admitted for increasing bleeding of a chronic Manubrium ulceration, 20 months after coronary artery bypass complicated by perioperative ascending aorta dissection requiring prosthetic graft replacement. One month later, he underwent epiploplasty for a mediastinitis followed by long-term antibiotic therapy. Five months later, he presented with a Manubrium ulceration of the sternotomy. Spiral computerized tomography (CT) and aortography revealed a 20 mm anterior peri-prosthetic false aneurysm with a wide neck. Advanced age, active mediastinitis and patient’s objection led us to perform percutaneous occlusion according to the Moret remodeling technique while protecting the coils release with balloon catheter inflation. Results: No post-operative complication was observed and at 1-year follow-up the patient was doing well with no recurrent bleeding. Magnetic resonance imaging (MRI) and spiral CT controls confirmed coils stability without any internal flow. Conclusion: Percutaneous coils embolization of a large false aneurysm in the ascending aorta can be a palliative treatment in a surgically unsuited patient.

Thermodynamic analysis of cavity creating mutations in an engineered leucine zipper and energetics of glycerol-induced coiled coil stabilization.

Protein stability in vitro can be influenced either by introduction of mutations or by changes in the chemical composition of the solvent. Recently, we have characterized the thermodynamic stability and the rate of folding of the engineered dimeric leucine zipper A(2), which has a strengthened hydrophobic core [Dürr, E., Jelesarov, I., and Bosshard, H. R. (1999) Biochemistry 38, 870-880]. Here we report on the energetic consequences of a cavity introduced by Leu/Ala substitution at the tightly packed dimeric interface and how addition of 30% glycerol affects the folding thermodynamics of A(2) and the cavity mutants. Folding could be described by a two-state transition from two unfolded monomers to a coiled coil dimer. Removal of six methylene groups by Leu/Ala substitutions destabilized the dimeric coiled coil by 25 kJ mol(-1) at pH 3.5 and 25 degrees C in aqueous buffer. Destabilization was purely entropic at around room temperature and became increasingly enthalpic at elevated temperatures. Mutations were accompanied by a decrease of the unfolding heat capacity by 0.5 kJ K(-1) mol(-1). Addition of 30% glycerol increased the free energy of folding of A(2) and the cavity mutants by 5-10 kJ mol(-1) and lowered the unfolding heat capacity by 25% for A(2) and by 50% for the Leu/Ala mutants. The origin of the stabilizing effect of glycerol varied with temperature. Stabilization of the parent leucine zipper A(2) was enthalpic with an unfavorable entropic component between 0 and 100 degrees C. In the case of cavity mutants, glycerol induced enthalpic stabilization below 50 degrees C and entropic stabilization above 50 degrees C. The effect of glycerol could not be accounted for solely by the enthalpy and entropy of transfer or protein surface from water to glycerol/water mixture. We propose that in the presence of glycerol the folded coiled coil dimer is better packed and displays less intramolecular fluctuations, leading to enhanced enthalpic interactions and to an increase of the entropy of folding. This work demonstrates that mutational and solvent effects on protein stability can be thermodynamically complex and that it may not be sufficient to only analyze changes of enthalpy and entropy at the unfolding temperature (T(m)) to understand the mechanisms of protein stabilization.

The Feasibility of Three-Dimensional Guglielmi Detachable Coil for Embolisation of Wide Neck Cerebral Aneurysms

The three-dimensional Guglielmi detachable coil is a modification of the conventional Guglielmi coil. It has a unique complex structure, with alternating small and large loops at 90 degrees angle to each other during deployment. The enhanced coil complexity optimizes coil purchase on the aneurysm wall, promoting coil stability within the aneurysm sac. It may be the solution of the single catheter technique in the embolisation of wide neck aneurysms.We report our early experience in the embolisation of wide neck aneurysms using these complex coils.

Abstracts of literature

Abstracts of literature

70MW級超電導発電機の界磁巻線の熱的安定性の検証

70MW級超電導発電機の界磁巻線の熱的安定性の検証

Proline Affects Oligomerization of a Coiled Coil by Inducing a Kink in a Long Helix

The structural effect of a proline in a helix in trifluoroethanol (TFE)/water medium was examined on a 29-mer peptide and its proline analog derived from the leucine zipper (LZ)-like motif of gp41 (the transmembrane glycoprotein of HIV-1) by NMR and circular dichroism (CD) spectroscopies. Lower helical content was found for the proline mutant from the CD study. NMR data show that distortion of the helix by proline is local and occurs mainly on the N-terminal side of the substitution site. Molecular dynamics computation exhibits a bending of the helical axis of 30° ± 10°, in agreement with X-ray diffraction results. Light-scattering experiments indicated that the average aggregation number of the proline-substituted mutant is substantially lower than that of the wild-type peptide. From the ratio of dissociation constants of the wild-type and the proline mutant peptides, the difference in free energy of trimeric formation is calculated to be 2.1 kcal/mol. Thermal stability, helicity, and the average aggregation number for the helix oligomers were found to be correlated. The structural alteration and the reduced coiled coil stability may account for the deficiency in the biological functions of the proline mutants of gp41 and in the inhibitory action of proline-substituted peptides. These effects may also be important in unraveling the roles played by proline in transmembrane proteins.

Clinical and angiographic results of endosaccular coiling treatment of giant and very large intracranial aneurysms: a 7-year, single-center experience.

To evaluate whether the objectives of surgical treatment, i.e., prevention of aneurysmal rebleeding, relief of aneurysmal mass effect, and prevention of embolic complications, are met by endosaccular coiling treatment applied to giant and very large wide-necked aneurysms. Thirty patients with 31 giant or very large aneurysms were considered to show unacceptable risk/benefit ratios for open surgery and were treated using the Guglielmi detachable coil (GDC) method between 1992 and 1998. With endosaccular GDC treatment, 73.3% of the population experienced excellent to good recoveries (Glasgow Outcome Scale scores of 4 or 5), with a 13.3% procedure-related morbidity rate and a 6.7% procedure-related mortality rate. Two hemorrhaging episodes occurred after GDC treatment (annual bleeding rate, 2.5%; 2 hemorrhaging episodes/79.2 patient-yr). Symptoms related to aneurysmal mass effect were improved for 45.5% of the patients presenting with signs of neural compression. Among 23 patients with 24 aneurysms who were available for angiographic follow-up assessment, complete or nearly complete occlusion was observed for 17 aneurysms (71%; angiographic follow-up period, 24.3 +/- 19.6 mo, mean +/- standard deviation). A single total embolization served as definitive treatment for only 12.5% of the giant aneurysms and 31% of the very large aneurysms. Endosaccular GDC treatment of giant and very large aneurysms was accomplished with procedure-related morbidity and mortality rates comparable to those for open surgery performed by experts. However, because coil stability was unsatisfactory, we suggest that the GDC method should currently be reserved for individuals who are considered poor candidates for open surgery.

Development of a 1 T/1 kA-class AC superconducting coil

In order to develop AC superconducting apparatus for power use, 10 kA/sub r.m.s./-class AC superconducting coils should be developed. From such a viewpoint, the authors have been investigating AC superconducting coils having a large AC transport current capacity. In this paper, the specification and experimental results of an 1 T/sub r.m.s.//1 kA/sub r.m.s./-class AC superconducting coil are shown. Two experimental AC coils using the sub-cable and single strand of this AC superconducting coil are also fabricated and tested to investigate the stability of AC coils. The quench current of each AC coil is measured and is compared to the DC critical current characteristics of the strand. From the result of the comparison, it is confirmed that the AC quench current of each superconducting coil is close to the DC quench current, and is close to the current which is determined by the critical current characteristics defined by 0.1 /spl mu/V/cm criterion. It is also confirmed that the quench point of the developed AC coil reaches to 1.396 T/sub peak//1288 A/sub peak/.

Design of structure and quench-stability of sector magnets for RIKEN superconducting ring cyclotron

Design, especially about the structure and quench stability, of the superconducting sector magnets for the RIKEN superconducting ring cyclotron is described. Special features of the sector magnets are the triangular shape superconducting coil, cold pole arrangement for supporting of the huge magnetic forces and the cryogenic stable coils. A full-scale superconducting model is now under construction as a prototype sector magnet.

Transarterial occlusion of patent ductus arteriosus with Gianturco coils in pediatric patients: a preliminary result in central Taiwan

Objective: We wish to present the preliminary result of transarterial occlusion of patent ductus arteriosus (PDA) with Gianturco coils in pediatric patients in central Taiwan. Materials and Methods: We attempted occlusion of PDA with Gianturco coils in a total of 26 consecutive patients, 13 infants and 13 children, 23 female and three male, between July 1 1997 to September 30 1998. Median patient age was 2.57 years (from 0.25 to 14.02 years old). Median patient weight was 10.8 kg (4.0 to 36.0 kg). Premature babies with PDA, full-term babies who were less than three months old and patients who had other congenital heart disease were not included in this study. All PDAs were approached transarterially from the femoral artery. Coils were selected to provide a helical diameter that was twice or more the minimum ductus diameter and a length approximating five loops. In five patients who had a PDA diameter ≥3.5 mm, we used a snare technique to assist coil delivery beforehand, and to test coil stability, or to retrieve coil that had migrated to the pulmonary artery afterwards. Physical auscultation, chest radiographs and echocardiography with color Doppler were done in all patients within 24 h, and one, two, three, six and 12 months after coil occlusion. Results. The median ductus minimum diameter was 2.3 mm (range, 1.0 to 4.7 mm). Fifteen patients had the megaphone type (type A), four had the window type (type B), five had the tubular type (type C), one had the aneurysmal type (type D) and one had the elongated conical type (type E). Twenty-one patients underwent single coil occlusion and five had multiple coils occlusion. Twenty-one patients had immediate angiographic closure of the ductus and disappearance of heart murmur at 15 min after the procedure. Dark-brown urine (hemoglobinuria) was found in one patient, 10 h after the first procedure, due to a mild residual ductal shunt. Two more coils were implanted in a second procedure that was performed within 24 h, and the ductus was completely occluded. The dark-brown urine regressed. At one month follow-up, four patients had mild residual ductal shunts, which were completely occluded by one more coil in three patients and by two more coils in the other patient. Malpositioned coils were deployed in five patients immediately after the procedure. In total, the closure rate at 15 min, within 24 h, and at one, two, three, six and 12 months were 81, 85, 85, 100, 100, 100 and 100%, respectively. In one year of follow-up, there was no instance of coil migration, ductus reopening or stenosis of the left pulmonary artery. Conclusions. Transarterial occlusion of PDA, with a Gianturco coil having approximately five loops, can be effectively achieved in patients with a minimum ductus diameter up to 4.7 mm. In patients with a ductus of more than 3.5 mm, the snare-assisted technique was employed advantageously to control coil delivery with accuracy and stability. Coil malposition or migration can be easily retrieved using a 10-mm Nitnol snare catheter. Hemoglobinuria, due to intravascular hemolysis, may regress within 24 h after the second attempt at coil implantation.

The role of position a in determining the stability and oligomerization state of alpha-helical coiled coils: 20 amino acid stability coefficients in the hydrophobic core of proteins.

We describe here a systematic investigation into the role of position a in the hydrophobic core of a model coiled-coil protein in determining coiled-coil stability and oligomerization state. We employed a model coiled coil that allowed the formation of an extended three-stranded trimeric oligomerization state for some of the analogs; however, due to the presence of a Cys-Gly-Gly linker, unfolding occurred from the same two-stranded monomeric oligomerization state for all of the analogs. Denaturation from a two-stranded state allowed us to measure the relative contribution of 20 different amino acid side chains to coiled-coil stability from chemical denaturation profiles. In addition, the relative hydrophobicity of the substituted amino acid side chains was assessed by reversed-phase high-performance liquid chromatography and found to correlate very highly (R = 0.95) with coiled-coil stability. We also determined the effect of position a in specifying the oligomerization state using ultracentrifugation as well as high-performance size-exclusion chromatography. We found that nine of the analogs populated one oligomerization state exclusively at peptide concentrations of 50 microM under benign buffer conditions. The Leu-, Tyr-, Gln-, and His-substituted analogs were found to be exclusively three-stranded trimers, while the Asn-, Lys-, Orn-, Arg-, and Trp-substituted analogs formed exclusively two-stranded monomers. Modeling results for the Leu-substituted analog showed that a three-stranded oligomerization state is preferred due to increased side-chain burial, while a two-stranded oligomerization state was observed for the Trp analog due to unfavorable cavity formation in the three-stranded state.

A distinct 14 residue site triggers coiled-coil formation in cortexillin I.

We have investigated the process of the assembly of the Dictyostelium discoideum cortexillin I oligomerization domain (Ir) into a tightly packed, two-stranded, parallel coiled-coil structure using a variety of recombinant polypeptide chain fragments. The structures of these Ir fragments were analyzed by circular dichroism spectroscopy, analytical ultracentrifugation and electron microscopy. Deletion mapping identified a distinct 14 residue site within the Ir coiled coil, Arg311-Asp324, which was absolutely necessary for dimer formation, indicating that heptad repeats alone are not sufficient for stable coiled-coil formation. Moreover, deletion of the six N-terminal heptad repeats of Ir led to the formation of a four- rather than a two-helix structure, suggesting that the full-length cortexillin I coiled-coil domain behaves as a cooperative folding unit. Most interestingly, a 16 residue peptide containing the distinct coiled-coil 'trigger' site Arg311-Asp324 yielded approximately 30% helix formation as monomer, in aqueous solution. pH titration and NaCl screening experiments revealed that the peptide's helicity depends strongly on pH and ionic strength, indicating that electrostatic interactions by charged side chains within the peptide are critical in stabilizing its monomer helix. Taken together, these findings demonstrate that Arg311-Asp324 behaves as an autonomous helical folding unit and that this distinct Ir segment controls the process of coiled-coil formation of cortexillin I.

Helical and coiled-coil-forming properties of peptides derived from and inhibiting human immunodeficiency virus type 1 integrase assessed by 1H-NMR--use of NH temperature coefficients to probe coiled-coil structures.

Human immunodeficiency virus type 1 integrase (HIV-1 IN) which catalyzes viral DNA integration into the host genome of infected cells represents an attractive target for AIDS therapy. We have previously demonstrated the ability of the IN-(147-175)-peptide derived from the catalytic core domain of HIV-1 IN to inhibit the enzyme activity in vitro. IN-(147-175)-peptide contains four heptad repeats and displays a high propensity for coiled-coil formation while its [P159]IN-(147-175)-peptide analog (Lys159-->Pro in the protein, Lys13-->Pro in the peptide) is unable to form a stable coiled-coil and is devoid of inhibitory activity [Sourgen, F., Maroun, R. G., Frère, V., Bouziane, M., Auclair, C., Troalen, F. & Fermandjian, S. (1996) Eur. J. Biochem. 240, 765-773]. Now, we report results from an NMR study on IN-(147-175)-peptide and [P159]IN-(147- 175)-peptide as well as on an optimized [E156, A163, A167]IN-(147-175)-peptide that is a better inhibitor of IN than IN-(147-175)-peptide. While in aqueous solution, IN-(147-175)-peptide and [P159]IN-(147-175)-peptide display only nascent helical features, [E156, A163, A167]IN-(147-175)-peptide exhibits 20% of helical content. In 20% trifluoroethanol/80% H2O, the helix content is the highest for [E156, A163, A167]IN-(147-175)-peptide (approximately 70%) and the lowest for [P159]IN-(147-175)-peptide (approximately 40%), due to a local helix break caused by the Pro residue. The NHs of residues in the two central helical heptads (a-g) of IN-(147-175)-peptide and [E156, A163, A167]IN-(147-175)-peptide display a regular periodic variation of their temperature coefficients in 20% trifluoroethanol. The b, c and f residues on the hydrophilic face of the amphipathic helix show high coefficients reflecting hydrogen bonded NHs, while the a and d residues on the hydrophobic face exhibit low coefficients, near random-coil values. The particular arrangement of the hydrophobic side-chains of a and d residues at the coiled-coil interface reduces the access of trifluoroethanol molecules to their amide groups. The inability of trifluoroethanol molecules to create interactions with the amide C=O groups, these being required to strengthen the intrahelical C=O...H-N hydrogen bonds, is the main cause for observation of heptadic a and d residues with low NH temperature coefficients. Such effects concern mostly the two central helical heptads of IN-(147-175)-peptide and [E156, A163, A167]IN-(147-175)-peptide implying that these ones are engaged in stable parallel coiled coils. Our results provide a link between the propensity of peptides for helix formation, their coiled-coil properties and their efficiency to inhibit IN.

Evaluation of the adsorptive immobilisation of horseradish peroxidase on PTFE tubing in flow systems for hydrogen peroxide determination using fluorescence detection

A simple means of immobilisation of horseradish peroxidase (HRP) on the inner wall of PTFE tubing by physical adsorption is described. The HRP-immobilised tubing was used to form a reaction coil that was inserted into a flow system. Various conditions influencing the reaction, immobilisation, desorption and stability of the reaction coil were evaluated by a flow injection method based on HRP-catalysed fluorescent reaction of H 2O 2 with p-hydroxyphenylpropionic acid as fluorogenic substrate. Re-immobilisation showed good reproducibility when 1% (w/v) sodium dodecyl sulphate (SDS) was used to desorb the denatured enzyme and proteins from the wall of PTFE tubing. The immobilised reaction coil is stable for at least a month if it is kept in buffered phosphate solution at pH 5.8 in a refrigerator. The immobilised coil was washed with 1.0×10 −4 mol L −1 substrate solution for 40 h at a flow rate of 1.5 mL min −1 without losing activity. When substrate and 200 nmol L −1 H 2O 2 were continuously reacted and flowed through the reaction coil, the response was stable for 7 h (equivalent to about 1400 150 μL injections of 600 nmol L −1 H 2O 2) and retained 79% of its activity after 26 h of continuous reaction. The immobilised HRP is very sensitive to bubbles introduced into the flow system. Linear relationships between fluorescence intensity and H 2O 2 concentration were obtained in the range 4–80 ng mL −1 with HRP solution and with the immobilised reaction coil system. The detection limit ( S/ N=3) was 2 nmol L −1 H 2O 2 in both cases. The relative standard deviations (8 replicates) for the detection of 4 and 80 nmol L −1 H 2O 2 were 5% and <1%, respectively.