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J B Jackson

Publications and source records attributed to J B Jackson.

At least 19 recordsLinked to original sources
PubMed1996

Interaction of nucleotides with the NAD(H)-binding domain of the proton-translocating transhydrogenase of Rhodospirillum rubrum.

Transhydrogenase catalyzes the reduction of NADP+ by NADH coupled to the translocation of protons across a membrane. The polypeptide composition of the enzyme in Rhodospirillum rubrum is unique in that the NAD(H)-binding domain (called Ths) exists as a separate polypeptide. Ths was expressed in Escherichia coli and purified. The binding of nucleotide substrates and analogues to Ths was examined by one-dimensional proton nuclear magnetic resonance (NMR) spectroscopy and by measuring the quenching of fluorescence of its lone Trp residue. NADH and reduced acetylpyridine adenine dinucleotide bound tightly to Ths, whereas NAD+, oxidized acetylpyridine adenine dinucleotide, deamino-NADH, 5'-AMP and adenosine bound less tightly. Reduced nicotinamide mononucleotide, NADPH and 2'-AMP bound only very weakly to Ths. The difference in the binding affinity between NADH and NAD+ indicates that there may be an energy requirement for the transfer of reducing equivalents into this site in the complete enzyme under physiological conditions. Earlier results had revealed a mobile loop at the surface of Ths (Diggle, C., Cotton, N. P. J., Grimley, R. L., Quirk, P. G., Thomas, C. M., and Jackson, J. B. (1995) Eur. J. Biochem. 232, 315-326); the loop loses mobility when Ths binds nucleotide; the reaction involves two steps. This was more clearly evident, even for tight-binding nucleotides, when experiments were carried out at higher temperatures (37 degrees C), where the resonances of the mobile loop were substantially narrower. The binding of adenosine was sufficient to initiate loop closure; the presence of a reduced nicotinamide moiety in the dinucleotide apparently serves to tighten the binding. Two-dimensional 1H NMR spectroscopy of the Ths-5'-AMP complex revealed nuclear Overhauser effect interactions between protons of amino acid residues in the mobile loop (including those in a Tyr residue) and the nucleotide. This suggests that, in the complex, the loop has closed down to within 0.5 nm of the nucleotide.

Biological Transport↗
PubMed1996

Mutation of Tyr235 in the NAD(H)-binding subunit of the proton-translocating nicotinamide nucleotide transhydrogenase of Rhodospirillum rubrum affects the conformational dynamics of a mobile loop and lowers the catalytic activity of the enzyme.

The Tyr residue in the mobile loop region of the soluble, domain I polypeptide (called Ths) of the proton-translocating transhydrogenase from Rhodospirillum rubrum has been substituted by Asn and by Phe. The recombinant proteins were expressed at high levels in Escherichia coli and purified to homogeneity. The two well defined resonances at 6.82 and 7.12ppm, observed in the one-dimensional proton NMR spectrum of wild-type protein, and previously attributed to the Tyr residue, were absent in both mutants. In the Tyr235 --> Phe mutant Ths, they were replaced by two new resonances at 7.26 and 7.33 ppm, characteristic of a Phe residue. In both mutants, narrow resonances attributable to Met residues (and in the Tyr235 --> Phe mutant, resonances attributable to Ala residues) were shifted relative to the wild type, but other features in the NMR spectra were unaffected. The conformational dynamics of the mobile loop closure in response to nucleotide binding by the protein were altered in the two mutants. The fluorescence emission from Trp72 was unaffected by both Tyr substitutions, and the fluorescence was still quenched by NADH. The mutant Ths proteins bound to chromatophore membranes depleted of their native Ths with undiminished affinity. In these reconstituted systems, the Km values for thio-NADP+ and NADH, during light-driven transhydrogenation, were similar to those of wild-type, but the kcat values were decreased about 2-fold. In reverse transhydrogenation, the Kmvalues for NADPH were slightly decreased in the mutants relative to wild-type, but those for acetyl pyridine adenine dinucleotide were increased about 10- and 13-fold, respectively, and the kcat values were decreased about 2- and 5-fold, respectively, in the Tyr235 --> Phe and Tyr235 --> Asn mutants. It is concluded that Tyr235 may contribute to the process of nucleotide binding and that substitution of this residue prevents proper functioning of the mobile loop in catalysis.

Asparagine↗
PubMed1996

Estimation of the H+/H- ratio of the reaction catalysed by the nicotinamide nucleotide transhydrogenase in chromatophores from over-expressing strains of Rhodospirillum rubrum and in liposomes inlaid with the purified bovine enzyme.

Two strains of Rhodospirillum rubrum were constructed in which, by a gene dosage effect, the transhydrogenase activity of isolated chromatophores was increased 7-10-fold and 15-20-fold, respectively. The H+/H- ratio (the ratio of protons translocated per hydride ion equivalent transferred from NADPH to an NAD+ analogue, acetyl pyridine adenine dinucleotide), determined by a spectroscopic technique, was approximately 1.0 for chromatophores from the over-expressing strains, but was only approximately 0.6 for wild-type chromatophores. Highly-coupled proteoliposomes were prepared containing purified transhydrogenase from beef-heart mitochondria. Using the same technique, the H+/H- ratio was close to 1.0 for these proteoliposomes. It is suggested that the mechanistic H+/H- ratio is indeed unity, but that a low ratio is obtained in wild-type chromatophores because of inhomogeneity in the vesicle population.

Animals↗
PubMed1995

Cyclic reactions catalysed by detergent-dispersed and reconstituted transhydrogenase from beef-heart mitochondria; implications for the mechanism of proton translocation.

Transhydrogenase from beef-heart mitochondria was solubilised with Triton X-100 and purified by column chromatography. The detergent-dispersed enzyme catalysed the reduction of acetylpyridine adenine dinucleotide (AcPdAD+) by NADH, but only in the presence of NADP+. Experiments showed that this reaction was cyclic; NADP(H), whilst remaining bound to the enzyme, was alternately reduced by NADH and oxidised by AcPdAD+. A period of incubation of the enzyme with NADPH at pH 6.0 led to inhibition of the simple transhydrogenation reaction between AcPdAD+ and NADPH. However, after such treatment, transhydrogenase acquired the ability to catalyse the (NADPH-dependent) reduction of AcPdAD+ by NADH. It is suggested that this is a similar cycle to the one described above. Evidently, the binding affinity for NADP+ increases as a consequence of the inhibition process resulting from prolonged incubation with NADPH. The pH dependences of simple and cyclic transhydrogenation reactions are described. Though more complex than those in Escherichia coli transhydrogenase, they are consistent with the view [Hutton, M., Day, J.M., Bizouarn, T. and Jackson, J.B. (1994) Eur. J. Biochem. 219, 1041-1051] that, also in the mitochondrial enzyme, binding and release of NADP+ and NADPH are accompanied by binding and release of a proton. The enzyme was successfully reconstituted into liposomes by a cholate dilution procedure. The proteoliposomes catalysed cyclic NADPH-dependent reduction of AcPdAD+ by NADH only when they were tightly coupled. However, they catalysed cyclic NADP(+)-dependent reduction of AcPdAD+ by NADH only when they were uncoupled eg. by addition of carbonylcyanide-p-trifluoromethoxyphenyl hydrazone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Conformational dynamics of a mobile loop in the NAD(H)-binding subunit of proton-translocating transhydrogenases from Rhodospirillum rubrum and Escherichia coli.

Transhydrogenase catalyses the reversible transfer of reducing equivalents between NAD(H) and NADP(H) to the translocation of protons across a membrane. Uniquely in Rhodospirillum rubrum, the NAD(H)-binding subunit (called Ths) exists as a separate subunit which can be reversibly dissociated from the membrane-located subunits. We have expressed the gene for R. rubrum Ths in Escherichia coli to yield large quantities of protein. Low concentrations of either trypsin or endoproteinase Lys-C lead to cleavage of purified Ths specifically at Lys227-Thr228 and Lys237-Glu238. Observations on the one-dimensional 1H-NMR spectra of Ths before and after proteolysis indicate that the segment which straddles the cleavage sites forms a mobile loop protruding from the surface of the protein. Alanine dehydrogenase, which is very similar in sequence to the NAD(H)-binding subunit of transhydrogenase, lacks this segment. Limited proteolytic cleavage has little effect on some of the structural characteristics of Ths (its dimeric nature, its ability to bind to the membrane-located subunits of transhydrogenase, and the short-wavelength fluorescence emission of a unique Trp residue) but does decrease the NADH-binding affinity, and does lower the catalytic activity of the reconstituted complex. The presence of NADH protects against trypsin or Lys-C cleavage, and leads to broadening, and in some cases, shifting, of NMR spectral signals associated with amino acid residues in the surface loop. This indicates that the loop becomes less mobile after nucleotide binding. Observation by NMR during a titration of Ths with NAD+ provides evidence of a two-step nucleotide binding reaction. By introducing an appropriate stop codon into the gene coding for the polypeptide of E. coli transhydrogenase cloned into an expression vector, we have prepared the NAD(H)-binding domain equivalent to Ths. The E. coli protein is sensitive to proteolysis by either trypsin or Lys-C in the mobile loop. Judging by the effect of NADH on its NMR spectrum and on the fluorescence of its Trp residues, the protein is capable of binding the nucleotide though it is unable to dock with the membrane-located subunits of transhydrogenase from R. rubrum.

Alanine Dehydrogenase↗
PubMed1995

The involvement of NADP(H) binding and release in energy transduction by proton-translocating nicotinamide nucleotide transhydrogenase from Escherichia coli.

Proton-translocating transhydrogenase was solubilised and purified from membranes of Escherichia coli. Consistent with recent evidence [Hutton, M., Day, J., Bizouarn, T. and Jackson, J.B. (1994) Eur. J. Biochem. 219, 1041-1051], at low pH and salt concentration, the enzyme catalysed rapid reduction of the NAD+ analogue AcPdAD+ by a combination of NADH and NADPH. At saturating concentrations of NADPH, the dependence of the steady-state rate on the concentrations of NADH and AcPdAD+ indicated that, with respect to these two nucleotides, the reaction proceeds by a ping-pong mechanism. High concentrations of either NADH or AcPdAD+ led to substrate inhibition. These observations support the view that, in this reaction, NADP(H) remains bound to the enzyme: AcPdAD+ is reduced by enzyme-bound NADPH, and NADH is oxidised by enzyme-bound NADP+, in a cyclic process. When this reaction was carried out with [4A-2H]NADH replacing [4A-1H]NADH, the rate was decreased by 46%, suggesting that the H- transfer steps are rate-limiting. In simple 'reverse' transhydrogenation, the reduction of AcPdAD+ was slower with [4B-2H]NADPH than with [4B-1H]NADPH when the reaction was performed at pH 8.0, but there was no deuterium isotope effect at pH 6.0. This indicates that H- transfer is rate-limiting at pH 8.0 and supports our earlier suggestion that NADP+ release from the enzyme is rate-limiting at low pH. The lack of a deuterium isotope effect in the reduction of thio-NADP+ by NADH at low pH is also consistent with the view that NADPH release from the enzyme is slow under these conditions. A steady-state rate equation is derived for the reduction of AcPdAD+ by NADPH plus NADH, assuming operation of the cyclic pathway. It adequately accounts for the pH dependence of the enzyme, for the features described above and for kinetic characteristics of E. coli transhydrogenase described in the literature.

Escherichia coli↗
PubMed1995

Properties of the soluble polypeptide of the proton-translocating transhydrogenase from Rhodospirillum rubrum obtained by expression in Escherichia coli.

Transhydrogenase, which catalyses the reduction of NADP+ by NADH coupled to proton translocation across a membrane, may be unique in the photosynthetic bacterium Rhodospirillum rubrum. Unlike the homologous enzyme from animal mitochondria and other bacterial sources, it has a water-soluble polypeptide, which exists as a dimer (Ths), that can be reversibly dissociated from the membrane component [Williams, R., Cotton, N. P. J., Thomas, C. M. & Jackson, J. B. (1994) Microbiology, 140, 1595-1604]. We have expressed the gene for Ths in cells of Escherichia coli under control of the tac promoter and a strong ribosome binding site. The protein, purified by column chromatography, fully reconstituted transhydrogenation activity to everted membrane vesicles of Rhs. rubrum that had been washed to remove Ths. The purified expressed protein was prepared in quantities over 100-fold greater than were obtained from wild-type Rhs. rubrum. The fluorescence spectrum of purified expressed Ths had an intense and unusually short wavelength emission maximum at 310 nm with shoulders at 298 and 322 nm. Time-resolved measurements indicated that the fluorescence decay was almost monoexponential with a lifetime of 5.2 ns. On denaturation with 4 M guanidine hydrochloride, the emission band shifted to 352 nm and decreased in intensity. In the native protein, the fluorophore was relatively inaccessible to quenching solutes, such as iodide ions and acrylamide. It is concluded that the fluorescence emission arises mainly from the single tryptophan residue of Ths (Trp72), which is locked into a rigid conformation and is located in highly non-polar environment. The 310-nm fluorescence of Ths was quenched by NADH, maximally to 46%. The apparent binding constant was 18 microM. The fluorescence of Ths-bound NADH was enhanced relative to the nucleotide in free solution and its emission maximum was shifted to a shorter wavelength (440 nm). These data support previous indications that the NADH binding site is located in domain I of proton-translocating transhydrogenase. Excitation of Ths at 280 nm did not lead to sensitized emission at 440 nm from bound NADH. This indicates that the quenching of fluorescence of Ths by NADH does not result from resonance energy transfer from Trp72 to the bound nucleotide. NAD+, NADP+ and NADPH had little effect on the protein fluorescence. The kinetics of quenching of Ths fluorescence by NADH were examined after mixing in a stopped-flow device. The 'on' rate constant for nucleotide binding was approximately 8 x 10(6) M-1 s-1 and the 'off' constant approximately 150 s-1.

Amino Acid Sequence↗
PubMed1995

Long-term follow-up of blood donors with indeterminate human immunodeficiency virus type 1 results on Western blot.

BACKGROUND: At present, tens of thousands of United States blood donors who are at low risk for human immunodeficiency virus type 1 (HIV-1) infection are indefinitely deferred. These persons are repeatably reactive for HIV-1 antibody in enzyme immunoassay (EIA) and are indeterminate in Western blot. STUDY DESIGN AND METHODS: To determine the significance and persistence of anti-HIV-1 reactivity in plasma from volunteer blood donors with HIV-1-indeterminate Western blots, 66 donors were retested for HIV-1 antibody by the same manufacturers' EIA and Western blot 5 to 7 years after the initial Western blot. In addition, donors' peripheral blood mononuclear cells were tested by polymerase chain reaction (PCR) for HIV-1 DNA gag sequences. RESULTS: Thirty-five (53%) of 66 donors were still repeatedly reactive for HIV-1 on EIA and indeterminate on Western blot, 23 (35%) were negative on EIA and indeterminate on Western blot, 7 (11%) were negative in EIA and Western blot, and 1 (2%) was repeatedly reactive on EIA and negative on Western blot. Donors with persistently indeterminate Western blots had a band pattern nearly identical to that on the original Western blot. No donor was positive in Western blot, p24 antigen, or PCR testing. No donor had signs or symptoms of HIV-1 infection. CONCLUSION: Long-term follow-up of Western blot-indeterminate blood donors does not reveal evidence of HIV-infection. A mechanism to return these donors to the donor pool should be considered.

Base Sequence↗
PubMed1995

Human immunodeficiency virus (HIV) type 1 infection status and in vitro susceptibility to HIV infection among high-risk HIV-1-seronegative hemophiliacs.

Blood samples were obtained from 16 hemophiliacs who had a 50%-94% defined risk of human immunodeficiency virus (HIV) type 1 infection on the basis of treatment history and from 14 controls not at risk for HIV infection. HIV-1 was not detected in any of 12 patient samples by cocultivation nor in 14 patient samples by the polymerase chain reaction. Peripheral blood cells from 7 seronegative hemophiliacs at highest risk of seroconversion (94%) were less susceptible to HIV-1 infection in vitro than were cells from healthy controls (P < .025, one-tailed Wilcoxon rank sum test). In contrast, the susceptibility to HIV-1 infection of lymphocytes from 6 seronegative hemophiliacs at moderate risk (50%-56%) of seroconversion did not differ from that of cells from controls or from high-risk hemophiliacs. Therefore, prolonged periods of seronegative HIV-1 infection are not common in this high-risk population. In addition, among hemophiliacs there may exist heterogeneity in susceptibility to HIV-1 infection in vitro and in vivo.

Adult↗
PubMed1995

Comparative stabilities of quantitative human immunodeficiency virus RNA in plasma from samples collected in VACUTAINER CPT, VACUTAINER PPT, and standard VACUTAINER tubes.

This study compared the levels of human immunodeficiency virus (HIV) virion RNA in plasma from whole blood collected in VACUTAINER CPT (cell preparation tube), VACUTAINER PPT (plasma preparation tube), VACUTAINER SST (serum separation tube), and standard VACUTAINER tubes with sodium heparin, acid citrate dextrose, sodium citrate, and potassium EDTA used as anticoagulants. Quantitative plasma HIV RNA levels were measured by branched-DNA signal amplification. Blood from all tubes was either processed within 1 to 3 h after collection or stored at room temperature or at 4 degrees C for analysis at 6 to 8 and 30 h postdraw. Immediately separated plasma from sodium citrate CPT tubes held at 4 degrees C maintained better stability of HIV RNA equivalents than whole blood held at room temperature or 4 degrees C. The highest number of HIV RNA equivalents was seen with EDTA VACUTAINER tubes. HIV RNA equivalents in all types of plasma were significantly higher than in SST tubes. Although a decline in HIV RNA equivalents was seen in all collection devices after 30 h, a significantly greater decline in plasma HIV RNA equivalents occurred in acid citrate dextrose VACUTAINER tubes than in citrate CPT, PPT, and standard EDTA VACUTAINER tubes. In order to minimize the variability of quantitative HIV RNA test results, our data suggest that samples collected for a particular assay should be processed at the same time postdraw using a particular tube type throughout a given study.

Anticoagulants↗
PubMed1995

A critical analysis of the use of radiation inactivation to measure the mass of protein.

Measurements are presented of the radiation inactivation of four enzymes exposed to a 6 MeV proton beam. It has long been thought that the measurement of the susceptibility of an enzyme to ionizing radiation can be used to determine its molecular mass. Results are frequently interpreted using the empirical analysis of Kempner and Macey (Biochim. Biophys. Acta 163, 188-203, 1963). We examine this analysis and discuss the validity and limitations of the assumptions on which it is based. Our results indicate that the specific biochemical properties of each enzyme make a significant contribution to its radiation sensitivity.

Animals↗
PubMed1994

Proton-translocating transhydrogenase and NAD- and NADP-linked isocitrate dehydrogenases operate in a substrate cycle which contributes to fine regulation of the tricarboxylic acid cycle activity in mitochondria.

H(+)-transhydrogenase (H(+)-Thase) and NADP-linked isocitrate dehydrogenase (NADP-ICDH) are very active in animal mitochondria but their physiological function is only poorly understood. This is especially so in the case of the heart and muscle, where there are no major consumers of NADPH. We propose here that H(+)-Thase and NADP-ICDH have a combined function in the fine regulation of the activity of the tricarboxylic acid (TCA) cycle, providing enhanced sensitivity to changes in energy demand. This is achieved through cycling of substrates by NAD-linked ICDH, NADP-linked ICDH and H(+)-Thase. It is proposed that NAD-ICDH operates in the forward direction of the TCA cycle, but NADP-ICDH is driven in reverse by elevated levels of NADPH resulting from the action of the transmembrane proton electrochemical potential gradient (delta p) on H(+)-Thase. This has the effect of increasing the sensitivity to allosteric modifiers of NAD-ICDH (NADH, ADP, ATP, Ca2+ etc), potentially giving rise to large changes in the net flux from iso-citrate to alpha-ketoglutarate. Furthermore, changes in the level of delta p resulting from changes in the demand for ATP would, via H(+)-Thase, shift the redox state of the NADP pool and this, in turn, would lead to a change in the rate of the reaction catalysed by NADP-ICDH and hence to an additional and complementary effect on the net metabolic flux from isocitrate to alpha-ketoglutarate. Other consequences of this substrate cycle are, (i) the production of heat at the expense of delta p, which may contribute to thermoregulation in the animal, and (ii) an increased rate of dissipation of delta p (leak).

Animals↗
PubMed1994

Kinetic resolution of the reaction catalysed by proton-translocating transhydrogenase from Escherichia coli as revealed by experiments with analogues of the nucleotide substrates.

The mechanism, by which transhydrogenase couples transfer of H- equivalents between NAD(H) and NADP(H) to the translocation of protons across a membrane, has been investigated in the solubilised, purified enzyme from Escherichia coli using analogues of the nucleotide substrates. The key observation was that, at low pH and ionic strength, solubilised transhydrogenase catalysed the very rapid reduction of acetylpyridine adenine dinucleotide (an analogue of NAD+) by NADH, but only in the presence of either NADP+ or NADPH. This indicates that the rates of release of NADP+ and NADPH from their binary complexes with the enzyme are slow. The dependences on pH and salt concentration suggest that (a) release of both NADP+ and NADPH are accompanied by the release of H+ from the enzyme and (b) increased ionic strength decreases the value of the pKa of the group responsible for H+ release. Modification of the enzyme with N,N1-dicyclohexylcarbodiimide led to inhibition of the rate of release of NADP+ and NADPH from the enzyme, but had a much smaller effect on the binding and release of NAD+, NADH and their analogues and on the interconversion of the ternary complexes of the enzyme with its substrates. It is considered that the binding and release of H+, which accompany the binding and release of NADP+/NADPH, might be central to the mechanism of proton translocation by the enzyme in its membrane-bound state.

Binding Sites↗
PubMed1994

Use of semiquantitative human immunodeficiency virus type 1 culture to guide therapy in a premature infant.

Semiquantitative cultures for human immunodeficiency virus type 1 were used to initiate and guide therapy in an asymptomatic, heavily infected premature infant. The cultures were performed on fivefold serial dilutions of peripheral blood mononuclear cells, and viral growth was detected by the appearance of p24 antigen in the supernatant. While the patient was receiving low-dose zidovudine, her titer diminished from 206 infectious units per 10(6) cells to undetectable levels over 20 weeks, and she remained asymptomatic throughout her 1st year of life. This case suggests that semiquantitative HIV-1 culture should be further evaluated for its ability to guide practical therapeutic decisions in patients who do not fulfill currently established criteria for treatment.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Cloning and sequencing of the genes for the proton-translocating nicotinamide nucleotide transhydrogenase from Rhodospirillum rubrum and the implications for the domain structure of the enzyme.

The genes for the proton-translocating nicotinamide nucleotide transhydrogenase from Rhodospirillum rubrum have been cloned using a probe constructed with the polymerase chain reaction, genomic DNA as target and oligonucleotide primers corresponding to amino acid sequence obtained from the purified soluble subunit. There is a cluster of three genes, designated pntAA, pntAB and pntB, whose translation products indicate polypeptides of 384, 139 and 464 amino acids, respectively. This contrasts with the situation in the enzymes from Escherichia coli (two polypeptides) and bovine mitochondria (one polypeptide) but there is close similarity between the sequences. PntAA is the soluble subunit of the enzyme from R. rubrum, equivalent to the relatively hydrophilic domain I that forms the N-terminal part of the alpha polypeptide of E. coli transhydrogenase and which probably contains the NAD(H)-binding site. PntAB corresponds to the strongly hydrophobic domain IIa at the C-terminus of the alpha polypeptide of the E. coli transhydrogenase. PntB corresponds to the E. coli beta polypeptide, which comprises the strongly hydrophobic domain IIb and the relatively hydrophilic domain III, thought to contain the NADP(H)-binding site. The peptide bond between PntAA-Lys237 and -Glu238 of both the denatured and the native soluble subunit is very sensitive to proteolysis by trypsin and the neighbouring peptide bond Lys227-Thr228 to cleavage by the endoproteinase Lys-C. Related sites have been reported to be sensitive to trypsin in the E. coli and bovine mitochondrial enzymes. The two tryptic fragments from the native R. rubrum soluble subunit are unable to reconstitute transhydrogenase activity to membranes depleted of the soluble subunit but they can block reconstitution by intact soluble subunit. It is suggested that this protease-sensitive region separates two subdomains and that, after trypsinolysis, at least one retains structural integrity and can dock with domains II and/or III.

Amino Acid Sequence↗
PubMed1994

Quality assurance and use of PCR in clinical trials.

Qualitative and quantitative HIV-1 DNA and RNA PCR assays are proving to be useful in the diagnosis of HIV-1 infection in infants and in assessing the in vivo antiviral activity of new therapies and regimens in clinical trials. The use of these standardized commercial assays in conjunction with an external quality assurance program has ensured that results from different laboratories are comparable. In addition, real-time proficiency monitoring has the potential to detect problems immediately before patient data are compromised.

Clinical Trials as Topic↗
PubMed1994

A phase I/II trial of intravenous L-2-oxothiazolidine-4-carboxylic acid (procysteine) in asymptomatic HIV-infected subjects.

Twenty-four asymptomatic, HIV-1-seropositive subjects with CD4 cell counts of > or = 400/microliters participated in a Phase I/II, dose escalation trial of intravenous L-2-oxothiazolidine-4-carboxylic acid (OTC: Procysteine). Four groups of six subjects each were consecutively assigned to receive OTC at an initial dose of 3, 10, 30, or 100 mg/kg, followed by the same dose given twice weekly for 6 weeks. Increases in whole-blood glutathione were observed in the highest dosage group after 6 weeks of therapy. No effects on changes in CD4 cell counts, viral load, or proviral DNA frequency were observed among the four dosage groups, although a decline in beta 2-microglobulin levels was apparent in the highest dosage group. One subject withdrew due to headaches; other probable adverse events including rash, flushing, pruritus, lightheadedness, and diminished concentration were self-limited.

Adult↗