The effects of bisulfite on growth and macromolecular synthesis in Escherichia coli

Bisulfite reversibly inhibits the growth of a variety of microorganisms and has been used as a preservative in foods and beverages for that reason. We have now measured macromolecule synthesis in Escherichia coli K12 after bisulfite treatment. RNA synthesis, the synthesis of total protein, and of an inducible enzyme, beta-galactosidase, stopped almost immediately upon addition of 2 mM (or higher concentrations) of bisulfite. These functions resumed after a lag whose duration depended on the concentration of bisulfite added. The synthesis of DNA was slowed upon bisulfite addition, but did not stop entirely. The inhibition of RNA synthesis by bisulfite took place in both stringent and relaxed strains of E. coli and was not relieved upon addition of chloramphenicol. Stringent control was therefore not involved in this effect. No effect on protein synthesis was observed in the cell-free system of E. coli (using poly(U) or MS2 RNA as messenger) at bisulfite concentrations up to 10 mM. Protein synthesis inhibition in vivo was apparently not due to a reaction of bisulfite with a component of this system. In additional experiments, RNA polymerase was not impaired by bisulfite, and the growth inhibition effect was shown to proceed in the presence of inhibitors of free radical chain reactions.     

Isolation of 3-(2-carboxyethyl)thymine following in vitro reaction of β-propiolactone with calf thymus DNA

3-(2-Carboxyethyl)thymine (3-CET) was synthesized from β-propiolactone (BPL) and dThd5′P at pH 9.0–9.5 via the intermediate 3-(2-carboxyethyl)thymidine-5′-monophosphoric acid (3-CEdThd5′P). 3-CEdThd5′P was converted to 3-CET by hydrolysis in 1.5 N HCl at 100°C for 2 h. The structure of 3-CET was assigned on the basis of UV spectra, electron impact (EI) and isobutane chemical ionization mass spectra and the EI mass spectrum of a trimethylsilyl derivative of 3-CET. BPL was reacted in vitro with calf thymus DNA at pH 7.5. 100 A units of BPL-reacted DNA yielded, following perchloric acid hydrolysis and preparative paper chromatography, 3 A units of 3-CET. Reaction of BPL with the phosphodiester thymidylyl-(3′-5′)thymidine gave 3-(2-carboxyethyl)thymidylyl-(3′-5′)-3-(2-carboxyethyl)thymidine (～3%). Phosphotriester formation was not detected.     

Synthesis and relative stereochemistry of the four mercapturic acids derived from styrene oxide and N-acetylcysteine

The chemical reaction between (±)-styrene oxide and N-acetylcysteine produces both positional isomers ($\text{1}$ and $\text{2}$) as a mixture of diastereoisomers with a preference for the benzylic thioether isomer $\text{1}$ (2 : 1). Synthesis of the mercapturic acid conjugates from either (+)- or (?)-styrene oxide produces only two of the four possible stereoisomers. The single diastereoisomers of $\text{1}$ and $\text{2}$ were separated by high pressure liquid chromatography (HPLC) and identified by ¹H- and ¹³C-nuclear magnetic resonance (NMR). The relative stereochemistry at the benzylic carbon center of the mercapturic acid conjugates was assigned on the basis of the established chemical correlation between optically pure styrene oxide and its precursor mandelic acid, and considerations on the mechanism of ring opening of epoxides by sulfur nucleophiles. The stereochemical definition of the isomers $\text{3}$–$\text{6}$ should prove useful in investigations of the biotransformation of the glutathione (GSH) conjugates of styrene oxide.     

Studies of copper(II) binding to glycylglycyl-L-tyrosine-N-methyl amide, a peptide mimicking the NH2-terminal copper(II)-binding site of dog serum albumin by analytical potentiometry, spectrophotometry, CD, and NMR spectroscopy

Unlike human serum albumin (HSA), dog serum albumin (DSA) does not possess the characteristics of the specific first binding site for Cu(II). In DSA, the important histidine residue in the third position, responsible for the Cu(II)-binding specificity in HSA, is replaced by a tyrosine residue. In order to study the influence of the tyrosine residue in the third position of DSA, a simple model of the NH2-terminal native sequence tripeptide of DSA, glycylglycyl-L-tyrosine-N-methylamide (GGTNMA) was synthesized and its Cu(II)-binding properties studied by analytical potentiometry, spectrophotometry, CD, and NMR spectroscopy. The species analysis indicated the existence of five mono-complexes at different protonation states: MHA, MA, MH-1A, MH-2A, MH-3A, and only one bis-complex MH-2A-2. The complexing ability of GGTNMA to Cu(II) was found to be weaker than that of the Cu(II) binding peptide models of HSA. The visible absorption spectra of Cu(II)-GGTNMA complexes are similar to those observed in the case of DSA-Cu(II) complexes. The weaker binding and the spectral properties of Cu(II)-GGTNMA complexes are consistent with less specific Cu(II)-binding properties of the peptide of this sequence similar to what was noted with DSA. CD results are in excellent agreement with species analysis and visible spectra where it is clearly evident that Cu(II) binds to GGTNMA starting from the alpha-NH2 group and step by step to deprotonated amide nitrogens as the pH is raised. The absence of any charge transfer band around 400 nm strongly indicates that Cu(II) does not bind to the phenolate group. Furthermore, NMR results are consistent with the noninvolvement of the tyrosine residue of GGTNMA in Cu(II) complexation. Thus, it is clear that the low Cu(II)-binding affinity of DSA is due to the genetic substitution of tyrosine for histidine at the NH2-terminal region of the protein.     

Mass spectrometric differentiation of leucine and isoleucine in proteins derived from bacteria or cell culture

The differentiation of leucine and isoleucine is a well known difficulty in mass spectrometric peptide sequencing. A technique has been developed which allows these two amino acids to be distinguished by growing a bacterial or cell culture in a medium containing γ,δ-dl-dideuteroleucine. The isotopically labelled residue is incorporated into the cell's proteins, and the resulting mass spectra of leucine containing peptides exhibit sequence ions 2 amu higher than the corresponding isoleucine peptides.     

Cloning and expression of a novel human C5orf12 gene,a member of the TMS_TDE family

We report here cloning and characterization of a novel human gene, termed C5orf12, which is a putative membrane protein belonging to the TMS_TDE family. The cDNA encodes 42 animo acid with a putative molecular weight of about 47 KDa. Secondary structure prediction showed that C5orf12 contained 10 putative transmembrane helices, which has high identity with other family members. We performed RT-PCR to examine its expression pattern. The result showed that C5orf12 was highly expressed in placenta, skeletal muscle, spleen, thymus, testis and peripheral leukocyte while expressed weakly in heart and liver. C5orf12 has high identity with the rat TPO1, so we speculate that C5orf12 may also have a role in the brain development.     

ND3, ND1 and 39 kDa subunits are more exposed in the de-active form of bovine mitochondrial complex I

An intriguing feature of mitochondrial complex I from several species is the so-called A/D transition, whereby the idle enzyme spontaneously converts from the active (A) form to the de-active (D) form. The A/D transition plays an important role in tissue response to the lack of oxygen and hypoxic deactivation of the enzyme is one of the key regulatory events that occur in mitochondria during ischaemia. We demonstrate for the first time that the A/D conformational change of complex I does not affect the macromolecular organisation of supercomplexes in vitro as revealed by two types of native electrophoresis. Cysteine 39 of the mitochondrially-encoded ND3 subunit is known to become exposed upon de-activation. Here we show that even if complex I is a constituent of the I + III₂ + IV (S₁) supercomplex, cysteine 39 is accessible for chemical modification in only the D-form. Using lysine-specific fluorescent labelling and a DIGE-like approach we further identified two new subunits involved in structural rearrangements during the A/D transition: ND1 (MT-ND1) and 39 kDa (NDUFA9). These results clearly show that structural rearrangements during de-activation of complex I include several subunits located at the junction between hydrophilic and hydrophobic domains, in the region of the quinone binding site. De-activation of mitochondrial complex I results in concerted structural rearrangement of membrane subunits which leads to the disruption of the sealed quinone chamber required for catalytic turnover.