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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Inhibition of the Vacuolar-like ATPase from Halobacterium saccharovorum by Thiol Reagents: Evidence for Different Functional Thiols

N-Ethylmaleimide (NEM) inhibited the vacuolar-like ATPase from Halobacterium saccharovorum (K(sub i) approximately 1 mM) by modifying one or more of the thiols located on the largest of the subunit. ATP protected against inhibition and coincidentally prevented NEM binding which suggested that NEM acts at or near the catalytic site. p-Chloromercuriphenylsulfonate (PCMS) also inhibited this ATPase (K(sub i) approximately 90 microM). ATP did not protect against PCMS inhibition. Dithiothreitol (DTT) partially reversed PCMS inhibition and restored approximately half of the initial activity of 90% inhibited enzyme. DTT did not restore activity of the NEM-inhibited enzyme or the PCMS-inhibited enzyme when it was subsequently incubated with NEM. The failure of ATP to protect against PCMS inhibition and the inability of DTT to restore activity of enzyme incubated in the presence of PCMS and NEM suggests these reagents react with different thiols and that the PCMS-sensitive thiol may have a structural role.

Hochstein, L. I.↗
NASA NTRS1985

Distribution and abundance of organic thiols

The role of glutathione (GSH) in protecting against the toxicity of oxygen and oxygen by products is well established for all eukaryotes studied except Entamoeba histolytica which lacks mitochrondria, chloroplasts, and microtubules. The GSH is not universal among prokaryotes. Entamoeba histolytica does not produce GSH or key enzymes of GSH metabolism. A general method of thiol analysis based upon fluorescent labeling with monobromobimane and HPLC separation of the resulting thiol derivatives was developed to determine the occurrence of GSH and other low molecular weight thiols in bacteria. Glutathione is the major thiol in cyanobacteria and in most bacteria closely related to the purple photosynthetic bacteria, but GSH was not found in archaebacteria, green bacteria, or GRAM positive bacteria. It suggested that glutathione metabolism was incorporated into eukaryotes at the time that mitochondria and chloroplasts were acquired by endosymbiosis. In Gram positive aerobes, coenzyme A occurs at millimolar levels and CoA disulfide reductases are identified. The CoA, rather than glutathione, may function in the oxygen detoxification processes of these organisms.

Fahey, R.↗
NASA NTRS1986

Evolution of thiol protective systems in prokaryotes

Biological thiols are essential elements in most aspects of cell function but undergo rapid oxidation to disulfides in the presence of oxygen. The evolution of systems to protect against such oxygen toxicity was essential to the emergence of aerobic life. The protection system used by eukaryotes is based upon glutathione (GSH) and GSH-dependent enzymes but many bacteria lack GSH and apparently use other mechanisms. The objective of this research is to elaborate the thiol protective mechanisms employed by prokaryotes of widely divergent evolutionary origin and to understand why GSH became the central thiol employed in essentially all higher organisms. Thiol-selective fluorescent labeling and HPLC analysis has been used to determine key monothiol components.

Fahey, R. C.↗
NASA NTRS1998

Prebiotic Amino Acid Thioester Synthesis: Thiol-Dependent Amino Acid Synthesis from Formose substrates (Formaldehyde and Glycolaldehyde) and Ammonia

Formaldehyde and glycolaldehyde (substrates of the formose autocatalytic cycle) were shown to react with ammonia yielding alanine and homoserine under mild aqueous conditions in the presence of thiol catalysts. Since similar reactions carried out without ammonia yielded alpha-hydroxy acid thioesters, the thiol-dependent synthesis of alanine and homoserine is presumed to occur via amino acid thioesters-intermediates capable of forming peptides. A pH 5.2 solution of 20 mM formaldehyde, 20 mM glycolaldehyde, 20 mM ammonium chloride, 23 mM 3-mercaptopropionic acid, and 23 mM acetic acid that reacted for 35 days at 40 C yielded (based on initial formaldehyde) 1.8% alanine and 0.08% homoserine. In the absence of thiol catalyst, the synthesis of alanine and homoserine was negligible. Alanine synthesis required both formaldehyde and glycolaldehyde, but homoserine synthesis required only glycolaldehyde. At 25 days the efficiency of alanine synthesis calculated from the ratio of alanine synthesized to formaldehyde reacted was 2.1%, and the yield (based on initial formaldehyde) of triose and tetrose intermediates involved in alanine and homoserine synthesis was 0.3 and 2.1%, respectively. Alanine synthesis was also seen in similar reactions containing only 10 mM each of aldehyde substrates, ammonia, and thiol. The prebiotic significance of these reactions that use the formose reaction to generate sugar intermediates that are converted to reactive amino acid thioesters is discussed.

Weber, Arthur L.↗
NASA NTRS1983

Nonenzymatic formation of energy-rich lactoyl and glyceroyl thioesters from glyceraldehyde and a thiol

The energy rich thioester, N-acetyl-S-lactoylcysteine, is formed under anaerobic conditions from glyceraldehyde and N-acetylcysteine at ambient temperature in aqueous solutions of sodium phosphate (pH 7.0). The conversion occurs at a rate of about 0.4% per day in reactions with 10 millimoles (mM) glyceraldehyde, 10 mM thiol, and 500 mM sodium phosphate (pH 7.0). Thioester formation proceeds at an estimated efficiency of 76%. The formation of lactoyl thioester most likely occurs by the phosphate catalyzed dehydration of glyceraldehyde to give pyruvaldehyde, which combines with thiol to form a hemithioacetal that rearranges to the thioester. A second energy rich thioester, N-acetyl-S-glyceroylcysteine, is also produced from glyceraldehyde when these reactions are carried out in the presence of oxygen and to a limited extent in the absence of oxygen. In the presence of oxygen the formation of glyceroyl thioester continues until the thiol disappears completely by oxidation. The significance of these reactions to the energetics of the origin of life is discussed.

Weber, A. L.↗
NASA NTRS1984

Nonenzymatic formation of 'energy-rich' lactoyl and glyceroyl thioesters from glyceraldehyde and a thiol

The energy rich thioester, N-acetyl-S-lactoylcysteine, is formed under anaerobic conditions from glyceraldehyde and N-acetylcysteine at ambient temperature in aqueous solutions of sodium phosphate (pH 7.0). The conversion occurs at a rate of about 0.4 percent per day in reactions with 10 millimoles (mM) glyceraldehyde, 40 mM thiol, and 500 mM sodium phosphate (pH 7.0). Thioester formation proceeds at an estimated efficiency of 76 percent. The formation of lactoyl thioester most likely occurs by the phosphate catalyzed dehydration of glyceraldehyde to give pyruvaldehyde, which combines with thiol to form a hemithioacetal that rearranges to the thioester. A second energy rich thioester, N-acetyl-S-glyceroylcysteine, is also produced from glyceraldehyde when these reactions are carried out in the presence of oxygen and to a limited extent in the absence of oxygen. In the presence of oxygen, the formation of glyceroyl thioester continues until the thiol disappears completely by oxidation. The significance of these reactions to the energetics of the origin of life is discussed.

Weber, A. L.↗
NASA NTRS1986

Thiol biochemistry of prokaryotes

The present studies have shown that GSH metabolism arose in the purple bacteria and cyanobacteria where it functions to protect against oxygen toxicity. Evidence was obtained indicating that GSH metabolism was incorporated into eucaryotes via the endosymbiosis giving rise to mitochrondria and chloroplasts. Aerobic bacteria lacking GSH utilize other thiols for apparently similar functions, the thiol being coenzyme A in Gram positive bacteria and chi-glutamylcysteine in the halobacteria. The thiol biochemistry of prokaryotes is thus seen to be much more highly diversified than that of eucaryotes and much remains to be learned about this subject.

Fahey, Robert C.↗
NASA NTRS1983

Occurrence of low molecular weight thiols in biological systems

Bromobimane labeling and high performance chromatography analysis were applied to various species of bacteria, plant tissues, and animal tissues. The reaction between thiols and monobromobimane is studied. Chromatograms revealing peaks produced by nonthiols and thiols are analyzed and compared. It is observed that all the bacteria species contain hydrogen sulfide, and glutathione is contained in facultative and aerobic gram-negative bacteria. For the plant tissues, the data reveal that mung bean sprouts contain homoglutathione and no glutathione; alfalfa sprouts contain homoglutathione and glutathione; the pea seed, nonlegumes, and fungi contain glutathione and no homoglutathione. It is detected that the main thiol in the animal tissues is glutathione. Based on the data, it is suggested that glutathione has an essential function in higher organisms.

Fahey, Robert C.↗
NASA NTRS2018

Infrared Spectra and Interstellar Sulfur: New Laboratory Results for H2S and Four Malodorous Thiol Ices

New infrared spectra are presented for H2S and four other sulfur-containing compounds, all thiols, at 10–140 K to aid in the study of interstellar and solar system ices. Infrared spectral changes on warming H2S and each thiol are described with an emphasis on the S–H stretching vibration at 2550–2525 cm(exp -1) (λ=3.92–3.96 μm) as it is in a relatively unobscured part of the infrared spectra of interstellar and planetary ices. Infrared positions and band strengths for each thiol’s S–H and C–H stretching vibrations are reported, along with the S–H band strength of H2S. Two band strengths of near-infrared features of CH3SH are included. Results for these compounds are compared, and some areas of agreement and disagreement with the literature are described.

Astrobiology↗
NASA NTRS2018

Infrared Spectra and Interstellar Sulfur: New Laboratory Results for H2S and Four Malodorous Thiol Ices

New infrared spectra are presented for H2S and four other sulfur-containing compounds, all thiols, at 10–140 K to aid in the study of interstellar and solar system ices. Infrared spectral changes on warming H2S and each thiol are described with an emphasis on the S–H stretching vibration at 2550–2525 cm(exp −1) (λ = 3.92–3.96 μm) as it is in a relatively unobscured part of the infrared spectra of interstellar and planetary ices. Infrared positions and band strengths for each thiol’s S–H and C–H stretching vibrations are reported, along with the S–H band strength of H2S. Two band strengths of near-infrared features of CH3SH are included. Results for these compounds are compared, and some areas of agreement and disagreement with the literature are described.

Astrochemistry; infrared: ISM; ISM: molecules; mol↗
NASA NTRS2018

Infrared Spectra and Interstellar Sulfur - New Laboratory Results for H2S and Four Malodorous Thiol Ices

New infrared spectra are presented for H2S and four other sulfur-containing compounds, all thiols, at 10–140 K to aid in the study of interstellar and solar system ices. Infrared spectral changes on warming H2S and each thiol are described with an emphasis on the S–H stretching vibration at 2550–2525 cm(exp −1) (λ = 3.92–3.96 μm) as it is in a relatively unobscured part of the infrared spectra of interstellar and planetary ices. Infrared positions and band strengths for each thiol’s S–H and C–H stretching vibrations are reported, along with the S–H band strength of H2S. Two band strengths of near-infrared features of CH3SH are included. Results for these compounds are compared, and some areas of agreement and disagreement with the literature are described.

Astrochemistry; infrared: ISM; ISM: molecules; mol↗
NASA NTRS1983

Thiol-catalyzed formation of lactate and glycerate from glyceraldehyde

The rate of lactate formation from glyceraldehyde, catalyzed by N-acetyl-cysteine at ambient temperature in aqueous sodium phosphate (pH 7.0), is more rapid at higher sodium phosphate concentrations and remains essentially the same in the presence and absence of oxygen. The dramatic increase in the rate of glycerate formation that is brought about by this thiol, N-acetylcysteine, is accompanied by commensurate decreases in the rates of glycolate and formate production. It is suggested that the thiol-dependent formation of lactate and glycerate occurs by way of their respective thioesters. Attention is given to the significance of these reactions in the context of molecular evolution.

Weber, A. L.↗
NASA NTRS2005

Electronic Transport through Self Assembled Thiol Molecules: Effect of Monolayer Order, Dynamics and Temperature

We present the charge transport and tunneling conductance of self assembled organic thiol molecules and discuss the influence of order and dynamics in the monolayer on the transport behavior and the effect of temperature. Conjugated thiol molecular wires and organometals such as terpyridine metal complexes provide a new platform for molecular electronic devices and we study their self assembly on Au(111) substrates by the scanning tunneling microscope. Determining the organization of the molecule and the ability to control the nature of its interface with the substrate is important for reliable performance of the molecular electronic devices. By concurrent scanning tunneling microscopy and spectroscopy studies on SAMs formed from oligo (phenelyne ethynelyne) monolayers with and without molecular order, we show that packing and order determine the response of a self assembled monolayer (SAM) to competing interactions. Molecular resolution STM imaging in vacuum shows that the OPES adopt an imcommensurate SAM structure on Au(111) with a rectangular unit cell. Tunneling spectroscopic measurements were performed on the SAM as a function of junction resistance. STS results show that the I-Vs are non linear and asymmetric due to the inherent asymmetry in the molecular structure, with larger currents at negative sample biases. The asymmetry increases with increasing junction resistance due to the asymmetry in the coupling to the leads. This is brought out clearly in the differential conductance, which also shows a gap at the Fermi level. We also studied the effect of order and dynamics in the monolayer on the charge transport and found that competing forces between the electric field, intermolecular interactions, tip-molecule physisorption and substrate-molecule chemisorption impact the transport measurements and its reliability and that the presence of molecular order is very important for reproducible transport measurements. Thus while developing new electronic platforms based on molecules, it is important to have a good control of the molecule-substrate interface, for the devices to perform reliably. While such a control would minimize fluctuations and dynamics in the ensemble, the real challenge is to develop device architectures that are tolerant to fluctuations, since they cannot be totally eliminated in these low dimensional soft systems. Results of temperature dependent STS measurements will also be discussed.

Dholakia, Geetha↗
NASA NTRS1988

Determination of low molecular weight thiols using monobromobimane fluorescent labeling and high-performance liquid chromatography

Methods are described for the preparation and high-performance liquid chromatography (HPLC) analysis of monobromobimane derivatives of low molecular weight thiols in extracts of biological samples. Typical problems encountered in the development and application of these methods are discussed. Analysis of mung bean extract is used as an example.

Fahey, Robert C.↗
NASA NTRS1995

Inhibition of the ATPase from Halobacterium Saccharovorum by Thiol Inhibitors: Evidence for the Presence of More Than One Essential Cysteinyl Residue

The vacuolar-like ATPase from Halobacterium saccha vorum is inhibited by N-ethylmaleimide and p-chloromercudphenylsulfonate. The failure of adenine nucleotides to protect against p-chloromercuriphenyisulfonate inhibition, of p-chloromercuriphenylsulfonate to protect against N-ethylmaleimide inhibition, and the difference in the temperature dependence of inactivation infers that the enzyme contains at least two thiols that are essential for enzyme activity. CNBr cleavage of C-14-N-ethylmaleimide labeled subunit results in two radioactive peptides that locates the N-ethylmaleimide-reactive cysteinyl residue as cysteine-262 in the H. salinarium sequence.

Hochstein, Lawrence I.↗