Simultaneous characterization of the reductive unfolding pathways of RNase B isoforms by top-down mass spectrometry

A novel method for characterization of the simultaneous reductive unfolding pathways of five isoforms of bovine pancreatic ribonuclease B (RNase B) is demonstrated. The results indicate that each isoform unfolds reductively through two three-disulfide-containing structured intermediates before proceeding to the fully reduced form, as in the reductive unfolding pathways of the A variant lacking the carbohydrate chain. The rates of reduction of bovine pancreatic ribonuclease A (RNase A) and RNase B and the formation and consumption of their reductive intermediates are identical, indicating that the unfolding events necessary to expose disulfide bonds for reduction are not affected by the oligosaccharide. The method utilizes top-down mass spectrometry and a naturally occurring tag on the protein, viz. the carbohydrate moiety, to obtain unfolding information of an ensemble of protein isoforms and is a generally applicable methodological advance for conducting folding studies on mixtures of different proteins.     

Development of a novel method to populate native disulfide-bonded intermediates for structural characterization of proteins: implications for the mechanism of oxidative folding of RNase A

RNase A, a model protein for oxidative folding studies, has four native disulfide bonds. The roles of des [40-95] and des [65-72], the two native-like structured three-disulfide-bonded intermediates populated between 8 and 25 degrees C during the oxidative folding of RNase A, are well characterized. Recent work focuses on both the formation of these structured disulfide intermediates from their unstructured precursors and on the subsequent oxidation of the structured species to form the native protein. The major obstacles in this work are the very low concentration of the precursor species and the difficulty of isolating some of the structured intermediates. Here, we demonstrate a novel method that enables the native disulfide-bonded intermediates to be populated and studied regardless of whether they have stable structure and/or are present at low concentrations during the oxidative folding or reductive unfolding process. The application of this method enabled us to populate and, in turn, study the key intermediates with two native disulfide bonds on the oxidative folding pathway of RNase A; it also facilitated the isolation of des [58-110] and des [26-84], the other two native-like structured des species whose isolation had thus far not been possible.     

Electron-transfer polymers. XXX. Preparation of poly(1-vinyl-3,4,6-trimethyl-2,5-benzoquinone)

1-Vinyl-3,4,6-trimethyl-2-methoxy-5-hydroxy-benzene (I) was prepared in good yield by the Wittig reaction from the corresponding chloromethyl compound. It could be polymerized cationically to low molecular weight material. The polymer could be oxidized to poly(1-vinyl-3,4,6-trimethyl-2,5-benzoquinone) (III) and could be reduced to the corresponding hydroquinone. Compound (I) was acetylated at the phenolic hydroxyl group and polymerized. The acetyl group was quantitatively reduced with lithium aluminum hydride, and the resulting polymer could be oxidized quantitatively to (III). Its molecular weight was a little higher than that prepared directly from (I).     

7-N,7'-N'-(1",2"-Dithianyl-3",6"-dimethylenyl)bismitomycin C: synthesis and nucleophilic activation of a dimeric mitomycin

Dimeric alkylating agents that modify complementary DNA strands have engendered significant interest. We have prepared the novel dimeric mitomycin, 7-N,7'-N'-(1",2"-dithianyl-3",6"-dimethylenyl)bismitomycin C (9), in which the mitomycins are bridged by a dithiane unit. Dimer 9, like the clinically tested acyclic disulfides KW-2149 (3) and BMS-181174 (4), was designed to activate under nucleophilic and reductive conditions. Successive nucleophile-mediated disulfide cleavage transformations of 9 are expected to generate thiol species ideally positioned to render the two mitomycin systems vulnerable to nucleophilic attack and permit DNA interstrand cross-link formation. The dithiane linker, strategically positioned between the two mitomycins, distinguished 9 from 3 and 4. Nucleophilic activation of this cyclic disulfide permitted both activated mitomycins to remain tethered to one another. We report the synthesis of 9, and show that the nucleophile Et(3)P markedly enhances the activation and consumption of 9, compared with the reference compound 7-N, 7"-N'-(cyclohexanyl-trans-1",4"-dimethylenyl)bismitomycin C (27). We further demonstrated that provides higher levels of DNA interstrand cross-links than either the dimeric reference compounds, and 7-N,7-N'-(2",5"-dihydroxy-1",6"-hexanediyl)bismitomycin C (28), or the monomeric mitomycins, 1 and 3, when Et(3)P is added to solutions containing EcoRI-linearized pBR322 DNA.     

A Miniature Electrolytic Conductivity Probe with a Wide Linear Range

A novel miniature electrolytic conductivity probe and its successful operation with modified bipolar pulse conductometry are presented. The probe based on a concentric ring‐disk electrode configuration of less than 1 mm in diameter featured extremely small detection volume, and conductivity was measured with a 1 μL solution. Rapid response, easy and quick washing, and virtually no consumption of samples by measurements were additional advantages of the suggested probe design. Poor linearity was observed with conventional AC conductometry due to a large cell constant and a small double layer capacitance of the probe. Measurement circuits for modified bipolar pulse conductometry were designed, and optimization of the various pulse parameters led to a wide linear dynamic range of 0.05–10 mS cm^?1, thus achieving high accuracy with a single‐point calibration. The suggested conductometric device could be conveniently applied to biological reagents and samples that are usually too little to be measured with conventional conductometers.     

Formation of new acid sites in dilute oxide solid solutions: A predictive model

A predictive model for the formation of new acid sites in a dilute solid solution of two component oxides is being developed by examining the electrostatic potential at the substituting cation site and the changes in the matrix necessary to balance the stoichiometry. When the prediction was used to compare with experimental results, the satisfactory comparison suggests that the electrostatic potential and the balance of stoichiometry are the two dominant factors in new acid site formation. The implications of this are discussed.     

Oxidative degradation of polystyrene

Nuclear magnetic resonance, infrared, and ultraviolet spectroscopy were used to elucidate the structure of oxidized polystyrene. To identify the nuclear magnetic resonance peaks of the degraded polystyrene, deuterated polystyrenes were synthesized and degraded. The primary structure present in the degraded polystyrene was found to be an aromatic carbonyl group. It was shown that this structure was formed regardless of the presence of ultraviolet light and was also present when polystyrene was degraded in carbon tetrachloride solution. When polystyrene was degraded in carbon tetrachloride solution, stable polymeric peroxides were formed in a concentration of 4 peroxide groups for every 1000 styrene units.     

Single etch patterning of stacked silver and molybdenum alloy layers on glass using microcontact wave printing

Stacked thin layers of silver alloy (AgPdCu) and MoCr layers on 10 x 15 cm2 glass substrates were patterned by microcontact wave printing and etching. Patterns of etch-resistant octadecanethiol self-assembled monolayers (SAMs) were wave printed with regular backplane stabilized PDMS stamps. Pattern development was achieved by etching both metal layers in a single step, employing a nitric acid-based etching bath. Trifluoroacetic acid and a nitrite salt were identified as essential bath components for a homogeneous etching process. Etch defects could be eliminated by the addition of a decanesulfonate, which stabilizes the SAM resist via a defect healing mechanism.     

The ground-state infrared spectra of aluminium monodeuteride: the mass-independent molecular parameters of group IIIa hydrides

The infrared spectra of the monodeuteride of aluminium has been measured in the gas phase in its ground electronic state (¹Σ) using a diode laser spectrometer. These experimental results were combined with those available for AlH from infrared Fourier transform spectra of the ν=2→0 sequence bands in order to calculate a set of mass-independent parameters and mass scaling coefficients. A set of Dunham parameters was also determined from the AlD data. The values of the mass scaling coefficients of the hydrides of four group IIIa metals are discussed.