Chemically resistant microfluidic valves from Viton® membranes bonded to COC and PMMA.

We present a reliable technique for irreversibly bonding chemically inert Viton® membranes to PMMA and COC substrates to produce microfluidic devices with integrated elastomeric structures. Viton® is widely used in commercially available valves and has several advantages when compared to other elastomeric membranes currently utilised in microfluidic valves (e.g. PDMS), such as high solvent resistance, low porosity and high temperature tolerance. The bond strength was sufficient to withstand a fluid pressure of 400 kPa (PMMA/Viton®) and 310 kPa (COC/Viton®) before leakage or burst failure, which is sufficient for most microfluidic applications. We demonstrate and characterise on-chip pneumatic Viton® microvalves on PMMA and COC substrates. We also provide a detailed method for bonding fluorinated Viton® elastomer, a highly chemically compatible material, to PMMA and COC polymers. This allows the production of microfluidic devices able to handle a wide range of chemically harsh fluids and broadens the scope of the microfluidic platform concept.

Temporal optimization of microfluidic colorimetric sensors by use of multiplexed stop-flow architecture.

We present two microfluidic architectures (continuous flow and multiplexed stop flow) for miniaturized colorimetric nutrient sensors. These systems are compared with respect to the temporal response (for optimization of sampling rate) and reduction of reagent consumption. The continuous-flow system is capable of a sampling rate of 60 samples·h(-1), limited by Taylor dispersion. The novel multiplexed stop-flow (MSF) microsystem architecture is not limited by dispersion. A demonstration MSF system consisting of two stop-flow channels is presented. This requires 12.6 s to load each sample into a measurement channel and when scaled would be capable of a throughput of 285 h(-1) (with full color development). The MSF architecture is manufactured in PMMA/Viton/PMMA [where PMMA = poly(methyl methacrylate)], utilizes on-chip valving, and is scalable, thereby permitting sampling at much faster rates (subsecond). Either system is capable of remote deployment and continuous measurement of nutrient concentrations. The MSF system is particularly suited for applications requiring high temporal or spatial resolution; such as from moving vehicles.

Mutations in SCO2 are associated with a distinct form of hypertrophic cardiomyopathy and cytochrome c oxidase deficiency.

Mutations in SCO2, a cytochrome c oxidase (COX) assembly gene located on chromosome 22, have recently been reported in patients with fatal infantile cardio-encephalomyopathy and severe COX deficiency in heart and skeletal muscle. The Sco2 protein is thought to function as a copper chaperone. To investigate the extent to which mutations in SCO2 are responsible for this phenotype, a complete sequence analysis of the gene was performed on ten patients in nine families. Mutations in SCO2 were found in three patients in two unrelated families. We detected two missense mutations, one of which (G1541A) results in an E140K substitution adjacent to the highly conserved CxxxC metal-binding site. The other (C1634T) results in an R171W substitution more distant from the copper-binding site. A nonsense codon was found on one allele in two siblings presenting with a rapidly progressive fatal cardio-encephalomyopathy. Interestingly, all patients so far reported are compound heterozygotes for the G1541A mutation, suggesting that this is either an ancient allele or a mutational hotspot. The COX deficiency in patient fibroblasts (approximately 50%) did not result in a measurable decrease in the steady-state levels of COX complex polypeptide subunits and could be rescued by transferring chromosome 22, but not other chromosomes. These data indicate that mutations in SCO2 cause a fatal infantile mitochondrial disorder characterized by hypertrophic cardiomyopathy and encephalopathy, and point to the presence of one or more other genes, perhaps in the copper delivery pathway, in this clinical phenotype.

Structure, functioning, and assembly of the ATP synthase in cells from patients with the T8993G mitochondrial DNA mutation. Comparison with the enzyme in Rho(0) cells completely lacking mtdna.

The structure and functioning of the ATP synthase of human fibroblast cell lines with 91 and 100%, respectively, of the T8993G mutation have been studied, with MRC5 human fibroblasts and Rho(0) cells derived from this cell line as controls. ATP hydrolysis was normal but ATP synthesis was reduced by 60% in the 100% mutants. Both activities were highly oligomycin-sensitive. The levels of F(1)F(0) were close to normal, and the enzyme was stable. It is concluded that the loss of ATP synthesis is because of disruption of the proton translocation step within the F(0) part. This is supported by membrane potential measurements using the dye JC-1. Cells with a 91% mutation load grew well and showed only a 25% loss in ATP synthesis. This much reduced effect for only a 9% difference in mutation load mirrors the reduced pathogenicity in patients. F(1)F(0) has been purified for the first time from human cell lines. A partial complex was obtained from Rho(0) cells containing the F(1) subunits associated with several stalk, as well as F(0) subunits, including oligomycin sensitivity conferring protein, b, and c subunits. This partial complex no longer binds inhibitor protein.

Mutation of the mitochrondrially encoded ATPase 6 gene modeled in the ATP synthase of Escherichia coli.

Defects of respiratory chain protein complexes and the ATP synthase are becoming increasingly implicated in human disease. Recently, mutations in the ATPase 6 gene have been shown to cause several different neurological disorders. The product of this gene is homologous to the a subunit of the ATP synthase of Escherichia coli. Here, mutations equivalent to those described in humans have been introduced into the a subunit of E. coli by site-directed mutagenesis, and the effects of these mutations on the ATPase activity, ATP synthesis and ability of the enzyme to pump protons studied in detail. The effects of the mutations varied considerably. The mutation L262P (9185 T-C equivalent) caused a 70% loss of ATP synthesis activity, reduced DCCD sensitivity, and lowered proton pumping activity. The L207P (8993 T-C equivalent) reduced ATP synthesis by 50%, affected DCCD sensitivity, while proton pumping was only marginally affected when measured by the standard AMCA quenching assay. The other mutations studied affected the functioning of the ATP synthase much less. The results confirm that modeling of these point mutations in the E. coli enzyme is a useful approach to determining how alterations in the ATPase 6 gene affect enzyme function and, therefore, how a pathogenic effect can be exerted.

The second stalk: the delta-b subunit connection in ECF1F0.

The ATP synthase F1F0 is the smallest molecular motor yet studied. ATP hydrolysis drives the rotary motion of the primary stalk subunits gamma and epsilon relative to the alpha 3 beta 3 part of F1. Evidence is reviewed to show that the delta and b subunits provide a second stalk that can act as a stator to facilitate these rotational movements.

Rotation of a gamma-epsilon subunit domain in the Escherichia coli F1F0-ATP synthase complex. The gamma-epsilon subunits are essentially randomly distributed relative to the alpha3beta3delta domain in the intact complex.

A triple mutant of Escherichia coli F1F0-ATP synthase, alphaQ2C/alphaS411C/epsilonS108C, has been generated for studying movements of the gamma and epsilon subunits during functioning of the enzyme. It includes mutations that allow disulfide bond formation between the Cys at alpha411 and both Cys-87 of gamma and Cys-108 of epsilon, two covalent cross-links that block enzyme function (Aggeler, R., and Capaldi, R. A. (1996) J. Biol. Chem. 271, 13888-13891). A cross-link is also generated between the Cys at alpha2 and Cys-140 of the delta subunit, which has no effect on functioning (Ogilvie, I., Aggeler, R., and Capaldi, R. A. (1997) J. Biol. Chem. 272, 16652-16656). CuCl2 treatment of the mutant alphaQ2C/alphaS411C/epsilonS108C generated five major cross-linked products. These are alpha-gamma-delta, alpha-gamma, alpha-delta-epsilon, alpha-delta, and alpha-epsilon. The ratio of alpha-gamma-delta to the alpha-gamma product was close to 1:2, i.e. in one-third of the ECF1F0 molecules the gamma subunit was attached to the alpha subunit at which the delta subunit is bound. Also, 20% of the epsilon subunit was present as a alpha-delta-epsilon product. With regard to the delta subunit, 30% was in the alpha-gamma-delta, 20% in the alpha-delta-epsilon, and 50% in the alpha-delta products when the cross-linking was done after incubation in ATP + MgCl2. The amounts of these three products were 40, 22, and 38%, respectively, in experiments where Cu2+ was added after preincubation in ATP + Mg2+ + azide. The delta subunit is fixed to, and therefore identifies, one specific alpha subunit (alphadelta). A distribution of the gamma and epsilon subunits, which is essentially random with respect to the alpha subunits, can only be explained by rotation of gamma-epsilon relative to the alpha3beta3 domain in ECF1F0.

Cross-linking of the delta subunit to one of the three alpha subunits has no effect on functioning, as expected if delta is a part of the stator that links the F1 and F0 parts of the Escherichia coli ATP synthase.

A mutant of the Escherichia coli F1F0-ATPase has been generated (alphaQ2C) in which the glutamine at position 2 of the alpha subunit has been replaced with a cysteine residue. Cu2+ treatment of ECF1 from this mutant cross-linked an alpha subunit to the delta subunit in high yield. Two different sites of disulfide bond formation were involved, i.e. between Cys90 (or the closely spaced Cys47) of alpha with Cys140 of delta, and between Cys2 of alpha and Cys140 of delta. Small amounts of other cross-linked products, including alpha-alpha, delta internal, and alpha-alpha-delta were obtained. In ECF1F0, there was no cross-linking between the intrinsic Cys of alpha and Cys140. Instead, the product generated between Cys2 of alpha and Cys140 of delta was obtained at near 90% yield. Small amounts of alpha-alpha and delta internal were present, and under high Cu2+ concentrations, alpha-alpha-delta was also formed. The ATPase activity of ECF1 and ECF1F0 was not significantly affected by the presence of these cross-links. When Cys140 of delta was first modified with N-ethylmaleimide in ECF1F0, an alpha-delta cross-link was still produced, although in lower yield, between Cys64 of delta and Cys2 of alpha. ATP hydrolysis-linked proton pumping of inner membranes from the mutant alpha2QC was only marginally affected by cross-linking of the alpha to the delta subunit. These results indicate that Cys140 and Cys64 of the delta subunit and Cys2 of the alpha subunit are in close proximity. This places the delta subunit near the top of the alpha-beta hexagon and not in the stalk region. As fixing the delta to the alpha by cross-linking does not greatly impair either the ATPase function of the enzyme, or coupled proton translocation, we argue that the delta subunit forms a portion of the stator linking F1 to F0.

Structure and arrangement of the delta subunit in the E. coli ATP synthase (ECF1F0).

F1F0 type ATPases are made up of two parts, an F1, which contains three catalytic sites on beta subunits, and an F0 which contains the proton channel. These two domains have been visualized in electron microscopy as linked by a narrow stalk of around 45 A in length. Biochemical studies have provided clear evidence that the gamma and epsilon subunits are components of this stalk. There is an emerging consensus that the gamma and epsilon subunits rotate relative to the alpha 3 beta 3 domain as part of the cooperativity and energy coupling within the complex. Two other subunits are required to link the F1 to F0 in the E. coli enzyme, and these are the delta and b subunits. The structure of a major part of the delta subunit (residues 1-134) has now been obtained by NMR spectroscopy. The main feature is a six alpha-helix bundle, which provides the N-terminal domain of the delta subunit. This domain interacts with the F1 core via the N-terminal part of the alpha subunit. The C-terminal domain of delta is less well defined. This part is required for binding to the F0 part by direct interaction with the b subunits. It is argued that delta and the two copies of the b subunit are components of a second stalk linking the F1 and F0 parts, which acts as a stator to allow the energy-linked rotational movements of delta and epsilon subunits.

Very long-chain acyl coenzyme A dehydrogenase deficiency presenting with exercise-induced myoglobinuria.

A young man presented with recurrent episodes of muscle pain and myoglobinuria after prolonged exercise or fasting. Studies on isolated muscle mitochondria showed slow flux through beta-oxidation and the presence of only saturated long-chain acyl coenzyme A (acyl-CoA) esters. These results strongly suggested a defect in the dehydrogenation of long-chain acyl-CoA esters that we confirmed by measurement of enzyme activity in muscle and platelet mitochondrial fractions and fibroblast homogenates. In all tissues studied from the patient, the enzyme activity was approximately 10% of control values with acyl-CoA esters from C16-C22 as substrates. We investigated the intramitochondrial location of the deficient acyl-CoA dehydrogenase by subfractionation of platelet mitochondria and, in contrast to the short-chain and medium-chain enzymes, which were localized in the soluble fraction, the majority of the acyl-CoA dehydrogenase activity with long-chain substrates was in the membrane fraction. These studies indicate that in humans, the predominant enzyme catalyzing the dehydrogenation of long-chain acyl-CoA esters is membrane-bound and that deficiency of this enzyme is a cause of muscle pain and rhabdomyolysis.

Immunoreactive enzyme protein in medium-chain acyl-CoA dehydrogenase deficiency.

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is a common inborn error of mitochondrial fatty acid oxidation. To determine if immunoreactive enzyme protein is present in patients with MCAD deficiency, we studied cultured skin fibroblasts from patients with the 985 point mutation, present in about 85% of cases, and cell lines from patients in which the point mutation is not present or only involves one allele. Immunoblotting studies, using a polyclonal antibody to the purified protein, showed an absence of immunoreactive protein in mitochondrial fractions prepared from fibroblasts from MCAD-deficient patients. To determine whether MCAD protein accumulated in the cytosol because of impaired transport into the mitochondria, we immunoprecipitated MCAD protein from the fibroblast homogenate. MCAD protein was detected in the immunoprecipitates from controls, but not in those from the MCAD-deficient patients. These results suggest that either the MCAD protein is not synthesised or, if produced, it is rapidly degraded.

Genetic analysis of quantitative characters in cigar and pipe tobacco Nicotiana tabacum II. Grades of cigar filler tobacco.

A diallel cross of four cigar and one pipe tobacco (Nicotiana tabacum L.) was analyzed for the following characters in samples of cured tobacco: (1) percentage of light filler; (2) percentage of heavy filler; (3) percentage of top filler; (4) percentage of bottom filler; (5) percentage of total filler; (6) percentage of marketable trash and (7) total percentage of marketable tobacco. The experiment was performed over three years with four replications. Analysis was done for general combining ability and specific combining ability. General combining ability was greater than specific combining ability for all parameters, although specific combining ability effects were also present for all parameters with the exception of total marketable tobacco. Reciprocal effects were completely absent. The line Pennbel 69 showed a negative general combining ability effect for all grades of filler, total filler and total marketable tobacco with a positive effect for percentage of marketable trash. High positive specific combining ability effects for percentage total filler and high negative specific combining ability effects for percentage marketable trash were shown by crosses of Pennbel 69 with the other four cultivars.