Chromium(III) modification of the first metal binding site of phosphoenolpyruvate carboxykinase

Chicken liver phosphoenolpyruvate carboxykinase (PEPCK) is activated by Cr2+ as the sole activator under anaerobic conditions. PEPCK was modified with Cr3+, starting with either Cr2+ or Cr3+. Cr3+ has the distinct advantage of being a paramagnetic cation that could serve as a paramagnetic probe. Activators Mn2+, Mg2+, and Co2+ protect against Cr3+ incorporation. EPR, CD, and fluorescence studies indicate that Cr3+ was incorporated into the cation binding site of PEPCK. The water proton relaxation rate (PRR) and fluorescence binding studies showed that Cr3+(n1)-PEPCK forms enzyme-substrate complexes similar to those observed for the Mn2+(n1)-PEPCK complex (n1 represents the metal "enzyme binding site" as opposed to the metal "nucleotide binding site"). Cr3+(n1)-PEPCK requires an additional divalent cation for activity, an indication of two metal sites on PEPCK. Cr3+(n1)-PEPCK retains 15% residual activity as compared to unmodified PEPCK and demonstrates normal Michaelis-Menten kinetics. This is the first report of an active Cr3+-modified enzyme complex.

Conformational changes in yeast pyruvate kinase studied by 205Tl+ NMR

The interaction of the monovalent cation with yeast pyruvate kinase (yPK) has been investigated by 205Tl+ NMR. TlNO3 activates yPK to 80-90% activity compared to KCl with an apparent Ka of 1.00 +/- 0.03 mM in the presence of 4 mM Mn(NO3)2 as the activating divalent cation. At higher concentrations of Tl+, enzyme inhibition is observed with an apparent KI of 180 +/- 10 mM. The extent of inhibition is dependent on the nature and concentration of the divalent cation. The effect of Mn2+ on the 1/T1 and 1/T2 values of 205Tl+ in the presence of yPK was determined at 173.02 MHz (300 MHz, 1H) and 346.03 MHz (600 MHz, 1H). The temperature dependence of the relaxation rates indicates that fast exchange conditions prevail for 205Tl+ longitudinal relaxation rates. The correlation time, tauc, for the Mn2+-205Tl+ interaction was estimated by a frequency dependence of 1/T1m for several enzyme complexes, and an average value of tauc was determined to be 0.91 ns. The distance between Tl+ and Mn2+ at the active site of yPK was calculated from the paramagnetic contribution of Mn2+ to the longitudinal (1/T1m) relaxation rates of Tl+ bound to yPK. For the apo yPK complex, the Tl+ to Mn2+ distance is 6.7 +/- 0.2 A. Upon addition of phosphoenolpyruvate (PEP) to form the yPK-Tl-Mn-PEP complex, the inter-cation distance decreases to 6.1 +/- 0.3 A. The addition of the allosteric activator fructose 1,6-bisphosphate (FBP) to form the yPK-Tl+-Mn2+-PEP-FBP complex gives an intermetal distance of 6.2 +/- 0.2 A. In the yPK-Tl-Mn-FBP complex, a Tl+-Mn2+ distance of 6.0 +/- 0.1 A is observed, indicating that FBP causes a conformational change at the active site in the absence of PEP. Analogous 205Tl NMR experiments with competitive inhibitors of PEP (oxalate, BrPEP) indicate that these ligands do not induce the same conformational changes as do the physiological substrates and activators. Similar experiments with the nonallosteric rabbit muscle PK were also performed and analyzed.

The allosteric regulation of pyruvate kinase by fructose-1,6-bisphosphate

BACKGROUND

Yeast pyruvate kinase (PK) catalyzes the final step in glycolysis. The enzyme therefore represents an important control point and is allosterically activated by fructose-1,6-bisphosphate (FBP). In mammals the enzyme is found as four different isozymes with different regulatory properties: two of these isozymes are produced by alternate splicing. The allosteric regulation of PK is directly related to proliferation of certain cell types, as demonstrated by the expression of an allosterically regulated isozyme in tumor cells. A model for the allosteric transition from the inactive (T) state to the active (R) state has been proposed previously, but until now the FBP-binding site had not been identified.

RESULTS

We report here the structures of PK from yeast complexed with a substrate analog and catalytic metal ions in the presence and absence of bound FBP. The allosteric site is located 40 A from the active site and is entirely located in the enzyme regulatory (C) domain. A phosphate-binding site for the allosteric activator is created by residues encoded by a region of the gene corresponding to the alternately spliced exon of mammalian isozymes. FBP activation appears to induce several conformational changes among active-site sidechains through a mechanism that is most likely to involve significant domain motions, as previously hypothesized.

CONCLUSIONS

The structure and location of the allosteric activator site agrees with the pattern of alternate genetic splicing of the PK gene in multicellular eukaryotes that distinguishes between a non-regulated isozyme and the regulated fetal isozymes. The conformational differences observed between the active sites of inactive and fully active PK enzymes is in agreement with the recently determined thermodynamic mechanism of allosteric activation through a 'metal relay' that increases the affinity of the enzyme for its natural phosphoenolpyruvate substrate.

Closed-loop subcutaneous insulin infusion algorithm with a short-acting insulin analog for long-term clinical application of a wearable artificial endocrine pancreas

Considering the management and safety of the insulin delivery route when a wearable artificial endocrine pancreas is applied to ambulatory diabetic patients on a long-term basis, we developed a s.c. insulin infusion algorithm by analyzing the dynamics of a s.c. injected short-acting insulin analog (Insulin Lispro) by a three-compartment model. Principally the insulin infusion algorithm was developed as a transfer function with the first-order delay in both proportional and derivative actions to blood glucose concentrations. The parameters for this algorithm were calculated to simulate a physiological plasma insulin profile as closely as possible. By applying this algorithm with regular insulin, diabetic patients showed a 2 h postprandial hyperglycemia and a delayed hyperinsulinemia, followed by hypoglycemic episodes 4-5 h after oral glucose load, just as observed in the computer simulation study. However, using Insulin Lispro, a near-physiological glycemic control (postprandial blood glucose of 153.1 +/- 8.3 mg/100 ml at 60 min and 90.3 +/- 7.1 mg/100 ml at 180 min, respectively) could be achieved without showing any delayed hyperinsulinemia or hypoglycemia. Daily glycemic excursions were also controlled near-physiologically and although the daily insulin requirement (731.7 +/- 160.5 mU/kg/day) was slightly higher, it was not significantly different from that with i.v. insulin infusion (622.3 +/- 142.6 mU/kg/day). These results indicate that the application of s.c. insulin infusion algorithm with Insulin Lispro is feasible for long-term glycemic control with a wearable artificial endocrine pancreas in ambulatory diabetic patients.

Affinity cleavage at the metal-binding site of phosphoenolpyruvate carboxykinase

Chicken liver phosphoenolpyruvate carboxykinase (PEPCK) was rapidly inactivated by micromolar concentrations of ferrous sulfate in the presence of ascorbate at pH 7.4. Omitting ascorbate or replacing the Fe2+ with Mn2+ or Mg2+ gives no inactivation. Mn2+, Mg2+, or Co2+ at 100-fold molar excess over Fe2+ offered complete protection from Fe2+/ascorbate-induced inactivation. The substrates PEP and GTP, but not OAA, GDP, or CO2, offered full protection from inactivation. The addition of 5 mM EDTA stopped further inactivation of the enzyme. Thermodynamic studies indicate that the inactive enzyme no longer binds Mn2+ but still had high affinity for GTP indicating that the inactivation process was specific for the metal site. A decrease in cysteine content was observed over time following PEPCK treatment with Fe2+ and ascorbate. The apparent first-order rate constant for free sulfhydryl loss (0.085 +/- 0.005 min-1) is similar to the apparent first-order rate constant for inactivation (0.067 +/- 0.005 min-1). Amino acid composition analysis revealed that cysteic acid was generated upon Fe2+/ascorbate addition to PEPCK. Native chicken liver PEPCK has an Mr of 67 kDa. SDS-PAGE of the inactivated enzyme showed the presence of two new bands at 31.7 and 35.3 kDa indicating that PEPCK was specifically cleaved at a single site. The rate of cleavage was slower than the rate of inactivation and fully inactivated enzyme was only 50% cleaved. The Fe2+/ascorbate-catalyzed inactivation was not solely due to protein cleavage. The protein fragments generated by cleavage were separated by C4 reverse phase HPLC. The cleavage exposed a new N-terminus which was identified to be the 35.3 kDa C-terminal half of PEPCK. Sequencing of the fragments indicated that the site of cleavage was between Asp296 and Ile297. These results indicate that Asp296 is involved in metal chelation. This agrees with previous studies [Hlavaty, J. J., & Nowak, T. (1997) Biochemistry 36, 3389-3403] that suggested that Asp295 and Asp296 are involved in metal binding.

Analysis of human plasma products: polymerase chain reaction does not discriminate between live and inactivated viruses

BACKGROUND

The viral safety of human plasma products is based on the careful selection of donors and donations and the removal and inactivation of human pathogenic viruses that could potentially contaminate human plasma. For the analysis of the final products for potential virus contamination, the use of polymerase chain reaction (PCR) has been proposed. To test whether this method can discriminate between infectious and inactivated viruses, the following studies were performed.

STUDY DESIGN AND METHODS

Infectious and virus-inactivated preparations were titrated with specific PCR, using viruses such as hepatitis B virus (HBV), hepatitis C virus, bovine viral diarrhea virus, and poliovirus. The inactivation method employed was pasteurization (10 hours, 60 degrees C) or solvent/detergent (SD) treatment; in the case of HBV, there was consecutive treatment by both methods.

RESULTS

Pasteurization of HBV and hepatitis C virus as well as SD treatment of HBV or pasteurization of HBV followed by SD treatment did not affect the detectability of these viruses by PCR, whereas an infectivity study in chimpanzees demonstrated that infectious hepatitis C virus was inactivated by pasteurization. Pasteurization also had no effect on the PCR titers of stabilized bovine viral diarrhea virus or poliovirus preparations, but it destroyed the infectivity of these viruses completely after only 4 hours' heat treatment.

CONCLUSION

Pasteurization or SD treatment destroys the infectivity of the viruses tested, but neither significantly affects their detectability by specific PCR. Therefore PCR is not a suitable measure for testing the viral safety of finished plasma products that have been subjected to virus inactivation.

Metal-ion-mediated allosteric triggering of yeast pyruvate kinase. 1. A multidimensional kinetic linked-function analysis

Regulation of the glycolytic pathway is considered to be primarily achieved by the carbon metabolites resulting from glucose metabolism [e.g., fructose 1,6-diphosphate (FDP), phosphoenolpyruvate (PEP), and citrate] and by the ATP charge of the cell. The divalent cations (e.g., Mg2+ and Mn2+) have not been considered as having regulatory roles in glycolysis, although they are involved in almost every enzyme-catalyzed reaction in the pathway. Using a kinetic linked-function analysis of steady-state kinetic data for the interactions of PEP, FDP, and Mn2+ with yeast pyruvate kinase (YPK), we have found that the divalent metal is the principal trigger of the allosteric responses observed with this enzyme. The interaction of Mn2+ to YPK enhances the interaction of FDP by -1.6 kcal/mol and the interaction of PEP by -2.8 kcal/mol. The simultaneous interaction of all three of these ligands to YPK is favored by -4.3 kcal/mol over the sum of their independent binding free energies. Surprisingly, the binding of the allosteric activator FDP does not directly influence the binding of the substrate PEP since a coupling free energy near zero was calculated for these two ligands. Thus, communication between the PEP and FDP sites occurs structurally through the metal by an allosteric relay mechanism. These conclusions are supported by results of a thermodynamic linked-function analysis of direct binding data for the interactions of PEP, FDP, and Mn2+ with YPK [Mesecar, A. D., & Nowak, T. (1997) Biochemistry (following paper in this series)]. Our findings raise important questions as to the possible roles of divalent metals in modulating multiligand interactions with YPK and in the regulation of the glycolytic pathway.

Metal-ion-mediated allosteric triggering of yeast pyruvate kinase. 2. A multidimensional thermodynamic linked-function analysis

A role has been proposed for the free divalent metal in triggering the allosteric responses of yeast pyruvate kinase based upon a kinetic linked-function analysis [Mesecar, A. D., & Nowak, T. (1997a) (preceding paper in this series)]. The major conclusion from the analysis is that the allosteric activator, fructose 1,6-diphosphate (FDP), does not directly communicate with the substrate, phosphoenolpyruvate (PEP), at the active site of the enzyme: it is Mn2+ that mediates the allosteric communication between the PEP and FDP sites in an allosteric relay mechanism. Assumptions were necessary to treat kinetic parameters as thermodynamic parameters, and the presence of the substrate ADP was necessary for the kinetic analysis. In this study, the influence of FDP on the interactions of PEP and Mn2+ and the influence of PEP and Mn2+ on the interaction of FDP with YPK were measured, where possible, by direct binding methods in the absence of ADP. Direct binding data were then subjected to a thermodynamic linked-function analysis for a heterotropic, three ligand coupled system in order to ascertain the two and three ligand coupling free energies. The two ligand coupling free energies deltaG(Mn-PEP), deltaG(Mn-FDP), and deltaG(PEP-FDP) are -3.88, -1.09, and -0.22 kcal/mol, respectively. These values indicate that positive, heterotropic interactions exist between each of these ligand pairs. The three ligand coupling free energy term, deltaG(Mn-PEP-FDP), indicates that simultaneous binding of Mn2+, PEP, and FDP is considerably favored over the sum of their independent binding free energies by -6.6 kcal/mol. These results demonstrate the key role of the metal in the modulation of ligand binding and are consistent with the values and the relationships of the kinetic parameters obtained from the kinetic linked-function analysis.

Formation and characterization of an active phosphoenolpyruvate carboxykinase-cobalt(III) complex

Avian mitochondrial phosphoenolpyruvate carboxykinase (PEPCK) was incubated with Co2+ and H2O2 to form a stable Co3+-PEPCK complex. PEPCK, similarly incubated with H2O2 and either Mg2+ or Mn2+, resulted in no significant loss in activity over 30 min. PEPCK, incubated with Co2+ and H2O2 at pH 7.4, showed rapid inhibition as observed by a 40% decrease in activity after 5 min. The loss of activity is linear with the incorporation of cobalt into PEPCK, resulting in 15-25% activity for the stoichiometric Co3+-PEPCK complex. The incorporation of and inhibition by Co3+ is protected by PEP and GTP (ITP). Treatment of the Co3+-PEPCK complex with beta-mercaptoethanol results in a loss of cobalt and full recovery of activity. The reduction and reactivation are protected by PEP and GTP (ITP). EPR, PRR, circular dichroism, and fluorescence studies all indicate that Co3+ has been selectively incorporated into the cation site of PEPCK, resulting in a catalytically active enzyme-cation species. The substrates form Michaelis complexes with Co3+-PEPCK, and the catalytic reaction occurs as a second sphere complex as previously suggested [Lee & Nowak (1984) Biochemistry 23, 6506); Duffy & Nowak (1985) Biochemistry 24, 1152]. Proteolytic digestion of the Co3+-PEPCK complex and isolation of the cobalt-containing peptide by reverse phase HPLC were performed to identify the location of the cation binding site. From mass, amino acid composition, and sequence analyses of the isolated cobalt-peptide, the region Thr276-Lys301 is responsible for metal chelation. This very homologous region, located in the central portion of PEPCK, contains two highly conserved aspartic acids, Asp295 and Asp296, that are the only feasible metal binding ligands.

Surgery in hemophilia A patients with factor VIII inhibitor: 10-year experience

Patients with hemophilia A and circulating anticoagulant (factor VIII inhibitor) present a difficult, even unsolvable problem, particularly if they require surgical treatment and the inhibitor titer is high. During the 1986-1995 period 29 surgical procedures on inhibitor hemophilia A patients were performed in our center. Each of the cases had an individual character, and all demanded special clinical treatment. Based on this experience we present the possibilities of hemostasis maintenance during the perioperative period with high doses of human or porcine factor VIII, aPCC, plasmapheresis, and extracorporeal antibody adsorption to protein A-Sepharose. In some patients hemostasis maintenance requires combined treatment. To induce immunotolerance in patients with inhibitor is the gold standard treatment because it is then possible to achieve proper hemostasis after factor VIII infusion. Various methods of immunotolerance induction have been discussed and compared with our experience with immunotolerance induction in 11 patients with small factor VIII doses (25 IU/kg twice a week) and the modified Malmö protocol in 15 patients.

Applications of nuclear magnetic resonance to determine the structure and interactions of ligands, peptides and enzymes

Nuclear magnetic resonance (NMR) spectroscopy is emerging as a powerful tool for the study of enzyme structure and function. This article discusses the general principles of NMR and the potential information this technique can provide in the study of enzymes along with its limitations.

Glycerophosphorylcholine, a component of both Ascaris suum muscle and Caenorhabditis elegans

Studies of the muscle phospholipid metabolism of Ascaris suum suggest an effect of cholinergic drugs on the turnover of phosphatidylcholine and the generation of glycerophosphorylcholine (GPC). 31P-nuclear magnetic resonance (NMR) studies of helminths revealed the presence of a major peak that was assigned to GPC. The primary effect of the cholinergic drugs on the parasites' phosphate profile appeared to be on the level of GPC. In in vivo studies, decreases in internal GPC concentrations occurred prior to any decrease in the concentration of ATP. The importance of these studies relies on the correct identity of this major 31P-NMR resonance. More recently, the identity of this resonance as GPC was questioned by experimental data obtained from C. elegans dauer larvae using the NMR technique. Because studies from our laboratory suggested that phospholipid metabolism may be intimately connected with the parasite's responses to drugs, the identity of the assigned resonance in the 31P-NMR spectrum as GPC in Ascaris suum was reexamined and found to be correct. Similar studies with C. elegans indicate the presence of both GPC and GPE.

Implantable electrocatalytic glucose sensor

An electrocatalytic glucose sensor for in vivo application has been developed to determine the glucose level in blood and further to control the insulin dosage in a closed loop system for diabetes therapy. The principle of the electrocatalytic glucose sensor is based on the direct electrochemical oxidation of glucose at a membrane-covered platinum electrode. For a possible clinical application the sensor was built as a catheter. A set of implantations in the vena cava of sheep demonstrated the potential feasibility of the sensor. The sensor values were simultaneously checked by the enzymatic analysis of glucose in blood samples drawn separately from a femoral vein. It was possible to determine the glucose concentration in sheep for more than 130 days with tolerable deviations from glucose reference measurements. The mean error was 2.5 mmol/l. One of the catheters was explanted after 211 days and the histological examination revealed a good biocompatibility of all materials used. In additional experiments, the differences of the glucose concentration in vena cava as well as in the anterior and posterior femoral veins of a sheep were examined during glucose tolerance tests. These experiments verified our method of in vivo calibration of the long-term implantable glucose sensor.

Electrocatalytic glucose sensor for long-term in vivo use

A catheter shaped electrocatalytic glucose sensor for in vivo application has been developed to determine the glucose level in blood and control the insulin dosage in a closed loop system for diabetes therapy. The principle of measurement is based on the electrochemical oxidation of glucose at a membrane-covered platium electrode. For various potential steps, the impedance obtained at two different frequencies is a function of the glucose concentration. A series of implantations in the vena cava of sheep demonstrated the potential feasibility of the sensor. It was possible to determine the glucose concentration in sheep for more than 130 days with tolerable deviations from glucose reference measurements. The mean error was 2.5 mmol/l. The catheter was explanted after 211 days and histological examination revealed a good biocompatibility of all materials used.

Electrocatalytic Glucose Sensor for Long-Term in vivo use

A catheter shaped electrocatalytic glucose sensor for in vivo application has been developed to determine the glucose level in blood and control the insulin dosage in a closed loop system for diabetes therapy. The principle of measurement is based on the electrochemical oxidation of glucose at a membrane-covered platinum electrode. For various potential steps, the impedance obtained at two different frequencies is a function of the glucose concentration. A series of implantations in the vena cava of sheep demonstrated the potential feasibility of the sensor. It was possible to determine the glucose concentration in sheep for more than 130 days with tolerable deviations from glucose reference measurements. The mean error was 2.5 mmol/l. The catheter was explanted after 211 days and histological examination revealed a good biocompatibility of all materials used.

[Splenectomy in adult patients with idiopathic thrombocytopenic purpura after intravenous immunoglobulin treatment]

Eight patients with idiopathic thrombocytopenic purpura (ITP) and no response to steroids therapy were prepared for splenectomy, for 5 consecutive days, with intravenous immunoglobulin (IVIG, 0.4 g/kg body weight). Increase of platelet counts and/or remission of haemorrhagic diathesis were observed in 7 patients, in one case IVIG proved ineffective. Splenectomy was performed in 7 cases and the postoperative course was uneventful. IVIG treatment has proved efficient in preparing ITP patients for splenectomy.

Inactivation of hepatitis A virus by heat treatment in aqueous solution

Hepatitis A virus infections have been reported recently among hemophilic patients in Italy and Germany, leading to speculation that infectious hepatitis A virus (HAV) might have been present in some factor VIII concentrates. In both cases, the implicated factor concentrates had been treated by a solvent/detergent method, which inactivates enveloped viruses but which would not be expected to inactivate HAV, a nonenveloped picornavirus. To determine whether HAV would be inactivated during pasteurization of factor VIII concentrate, an alternative method employed for virus inactivation, we determined the extent to which the infectivity of cell culture-adapted HAV, suspended either in cell culture medium or in a proprietary stabilizing buffer, was reduced by heat treatment at 60 degrees C for 10 hr. The titer of infectious HAV declined rapidly at 60 degrees C, but the stabilizer considerably delayed HAV inactivation. In cell culture medium, HAV was inactivated by > 3.6 log10 within 30 min, but 3.6 log10 inactivation of HAV was reached only after 6 hr in the presence of the stabilizer. Residual infectious HAV was present after even 10 hr of heat treatment in the stabilizer, indicating that < 5.2 log10 infectious HAV particles are inactivated under these conditions. In the presence of the stabilizer, HAV was significantly more stable than poliovirus type 1, which has been used to validate virus inactivation by pasteurization. We conclude that pasteurized factor VIII concentrate should pose little if any risk for transmission of HAV if pooled plasma used for its manufacture contained low levels of the virus.

Follow-up of hepatitis C virus infection in chimpanzees: determination of viraemia and specific humoral immune response

Chimpanzees were inoculated intravenously with the H strain of hepatitis C virus (HCV), and analysed for viraemia using the polymerase chain reaction and for a humoral immune response using first and second generation anti-HCV ELISAs and an immunoblot assay (4-RIBA). In all seven chimpanzees studied, viraemia occurred several weeks before a significant increase in serum alanine transferase (ALT) activity, whereas the first circulating anti-HCV antibodies became detectable at the time of significant increase in ALT levels, provided the second generation ELISA or 4-RIBA was used. On the basis of the duration of viraemia the chimpanzees studied could be assigned to two different groups: those in which viraemia disappeared in conjunction with or shortly after seroconversion, and those remaining viraemic for many weeks after the appearance of antibodies. The clearance of HCV from the circulation did not correlate with the antibody pattern determined using 4-RIBA, i.e. the HCV-specific assays currently available do not enable us to predict whether an infected chimpanzee will develop persistent viraemia. Only two of the seven chimpanzees analysed developed anti-core protein (c-22) antibodies, which appeared at the same time as the first ALT peak, whereas all animals developed antibodies to the non-structural protein, c-33, and these antibodies persisted.

25Mg NMR studies of yeast enolase and rabbit muscle pyruvate kinase

25Mg NMR spectroscopy was used to study the interactions of the activating cations with their respective binding sites in the enzymes yeast enolase and rabbit muscle pyruvate kinase (PK). Titration of Mg2+ with enolase allows for the calculation of 1/T2 for Mg2+ bound at site I of 1510 s-1 and a quadrupolar coupling constant chi = 0.30 MHz. Titration of Mg2+ with enolase in the presence of 2-phosphoglycerate (PGA) and Zn2+, where Zn2+ binds specifically at site I, gives a 1/T2 for Mg2+ bound at site II of 4000 s-1 (chi = 0.49 MHz). The Mg2+ at site II appears to be more anisotropic than Mg2+ at site I. The titration of site I of the enolase-Mg-PGA-Mg complex with Zn2+ or Mn2+ shows a simple displacement of the Mg2+. No paramagnetic effects by Mn2+ on 25Mg relaxation were observed. Temperature studies of the 25Mg resonance show that fast exchange of the Mg2+ occurs under these conditions. From the lack of a paramagnetic effect, the distance between the cations at sites I and II must be more than 6-9 A. This distance limits the location, hence the function, of the cation at site II for catalytic activity. Titration of Mg2+ with PK gives a 1/T2 for bound Mg2+ of 2200 s-1 (chi = 0.24 MHz). A titration of Mg2+ with PK in the presence of the inhibitor oxalate gives a 1/T2 of 400 s-1. The temperature dependence of 25Mg relaxation in the PK-Mg-oxalate complex is consistent with slow exchange (Ea = 6.1 +/- 1.6 kcal/mol). The enzyme-bound cation is more tightly sequestered by the addition of a ligand that binds directly to the cation. An investigation of the 25Mg relaxation in the PK-Mn-oxalate-Mg-ATP complex, where the Mg2+ is bound to the nucleotide and the Mn2+ was enzyme bound, was not successful due to precipitation of PK under experimental conditions and the short T2 relaxation for 25Mg in this complex. The applications of 25Mg NMR have been useful in partially describing the properties of the bound Mg2+ in these two metal-requiring enzymes.

Virus safety of human immunoglobulins: efficient inactivation of hepatitis C and other human pathogenic viruses by the manufacturing procedure

Human immunoglobulins are plasma derivatives with a low risk of transmitting viral infections. To the present, no proven case of human immunoglobulins transmitting human immunodeficiency viruses has been reported. However, there have been a few reports on the transmission of hepatitis C virus by these plasma proteins. To improve further the safety of both 5s iv human immunoglobulins and 7s im immunoglobulins, we introduced a 10-hour heat treatment of the aqueous solutions at 60 degrees C (i.e., pasteurization) into the manufacturing procedure. This treatment was not added to the manufacturing procedure of 7s iv immunoglobulin that already contained the S-sulfonation as a virus inactivating method. We now report on experimental data that show that the whole manufacturing procedures of the above immunoglobulins inactivate efficiently hepatitis C virus and that the specific virus inactivation methods alone, namely, pasteurization or S-sulfonation, also inactivate completely viruses of the flavivirus family, to which the hepatitis C virus belongs. The inactivation of the Flaviviridae bovine viral diarrhea virus, tick-borne encephalitis virus, and yellow fever virus by pasteurization or S-sulfonation was at least 10(5). The clearance of HCV achieved by the entire manufacturing process of each of these immunoglobulins was also at least 10(5). The experiments therefore show that pasteurization or S-sulfonation provides a high margin of safety to human immunoglobulins regarding the transmission of hepatitis C virus.