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At least 127 records · Page 7Linked to original sources
PubMed2004

Electron capture dissociation at low temperatures reveals selective dissociations.

Electron capture dissociation at 86 K of the linear peptide Substance P produced just two backbone fragments, whereas at room temperature eight backbone fragments were formed. Similarly, with the cyclic peptide gramicidin S, just one backbone fragment was formed at 86 K but five at room temperature. The observation that some backbone scissions are active and others inactive, when all involve NC(alpha) cleavages and have a high rate constant, indicates that the more specific fragments at low temperatures reflects the reduced conformation heterogeneity at low temperatures. This is supported by reduced or inactive hydrogen loss, a channel that has previously been shown to be affected by conformation. The conclusion that the ECD fragments are a snapshot of the conformational (intramolecular solvation shell) heterogeneity helps explain how the relative intensities of ECD fragments can be different on different instrument and highlights the common theme in methodologies used to increase sequence coverage, namely an increase in the conformational heterogeneity of the precursor ion population.

Cold Temperature↗
PubMed2006

Collisionally activated dissociation and electron capture dissociation of several mass spectrometry-identifiable chemical cross-linkers.

One of the challenges in protein interaction studies with chemical cross-linking stems from the complexity of intra-, inter-, and dead-end cross-linked peptide mixtures. We have developed new cross-linkers to study protein-protein interactions with mass spectrometry to improve the ability to deal with this complexity. Even the accurate mass capabilities of FTICR-MS alone cannot unambiguously identify cross-linked peptides from cell-labeling experiments due to the complexity of these mixtures resultant from the enormous number of possible cross-linked species. We have developed novel cross-linkers that have unique fragmentation features in the gas phase. The characteristics of these cross-linkers combined with the accurate mass capability of FTICR-MS can help distinguish cross-linking reaction products and assign protein identities. These cross-linkers that we call protein interaction reporters (PIRs) have been constructed with two reactive groups attached through two bonds that can be preferentially cleaved by low-energy CID of the respective protonated precursor ions. After cleavage of the labile bonds, the middle part of the linker serves as a reporter ion to aid identification of cross-linked peptides. This report highlights three new PIRs with new features that have been developed to improve the efficiency of release of reporter ions. The new cross-linkers reported here were tuned with the addition of an affinity tag, a hydrophilic group, a photocleavable group, and new low-energy MS/MS cleavable bonds. This report presents our investigation of the MSMS fragmentation behavior of selected protonated ions of the new compounds. The comprehensive fragmentation of these PIRs and PIR-labeled cross-linked peptides with low-energy collisions and an example of electron capture dissociation in FTICR-MS is presented. These new cross-linkers will contribute to current systems biology research by allowing acquisition of global or large-scale data on protein-protein interactions.

Cross-Linking Reagents↗
PubMedDate not supplied

Assessment of experimental bond dissociation energies using composite ab initio methods and evaluation of the performances of density functional methods in the calculation of bond dissociation energies.

Composite ab initio CBS-Q and G3 methods were used to calculate the bond dissociation energies (BDEs) of over 200 compounds listed in CRC Handbook of Chemistry and Physics (2002 ed.). It was found that these two methods agree with each other excellently in the calculation of BDEs, and they can predict BDEs within 10 kJ/mol of the experimental values. Using these two methods, it was found that among the examined compounds 161 experimental BDEs are valid because the standard deviation between the experimental and theoretical values for them is only 8.6 kJ/mol. Nevertheless, 40 BDEs listed in the Handbook may be highly inaccurate as the experimental and theoretical values for them differ by over 20 kJ/mol. Furthermore, 11 BDEs listed in the Handbook may be seriously flawed as the experimental and theoretical values for them differ by over 40 kJ/mol. Using the 161 cautiously validated experimental BDEs, we then assessed the performances of the standard density functional (DFT) methods including B3LYP, B3P86, B3PW91, and BH&HLYP in the calculation of BDEs. It was found that the BH&HLYP method performed poorly for the BDE calculations. B3LYP, B3P86, and B3PW91, however, performed reasonably well for the calculation of BDEs with standard deviations of about 12.1-18.0 kJ/mol. Nonetheless, all the DFT methods underestimated the BDEs by 4-17 kJ/mol in average. Sometimes, the underestimation by the DFT methods could be as high as 40-60 kJ/mol. Therefore, the DFT methods were more reliable for relative BDE calculations than for absolute BDE calculations. Finally, it was observed that the basis set effects on the BDEs calculated by the DFT methods were usually small except for the heteroatom-hydrogen BDEs.

Journal Article↗
PubMed1978

Dissociation of the atrioventricular node in acute inferior wall myocardial infarction. 1. Transverse dissociation (alternate Wenckebach periods).

Two cases of alternate Wenckebach periods developing during the acute phase of inferior wall myocardial infarction are presented. In both cases, syncope occurred and severe bradyarrhythmia was recorded on the day of admission. Electrophysiologic study performed in one patient and a narrow QRS complex in the other patient during the alternate Wenckebach periods confirmed the atrioventricular node as the level of block. Transverse dissociation of the atrioventricular node with two (or more) levels of block is the most acceptable explanation for this phenomenon. We suggest that alternate Wenckebach periods occurring during the acute phase of inferior wall myocardial infarction is a severe bradyarrhythmia, and prophylactic temporary pacing is recommended.

Acute Disease↗
PubMedDate not supplied

Complete intraventricular dissociation. Electrocardiographic manifestation of a rare intracardiac complete dissociation.

Complete Intraventricular Dissociation manifesting as dual ventricular rhythm was observed on surface electrocardiography in two middle-aged males with acute myocardial infarction. The first patient had a dominant accelerated (AV) junctional rhythm, and there was a sudden emergence of an additional independent slow and regular idioventricular escape rhythm. These ventricular complexes were bizarre and markedly widened, waveform with prolonged undulating electric potentials. In the second case, the emergence of a dominant idioventricular rhythm was coexistent with an additional independent escape rhythm with monophasic wider agonal ventricular complexes. Terminal tracings recorded later were essentially the same, except that an ill sustained ventricular fibrillation had replaced the ectopic agonal beats, and there was an enhanced automaticity in the dominant ventricular part. The sites of ectopic ventricular rhythms were thought to be in the ischaemic damaged ventricular myocardium, with a surrounding zone of conduction block.

Adult↗
PubMedDate not supplied

[Intraglobular electrostatic field of an enzyme. Calculation of the dissociation constant of a protein ionogenic group. Dissociation of Asp-102 chymotrypsin].

Factors determining the change of dissociation constants of ionogenic groups upon their transfer from water into a protein globule are considered. The change of the short-range interaction is simulated with the aid of two model solvents: dimethylformamide (DMF) and formamide (FA). The change of Bornian solvation energy is calculated taking into account the interaction of ions situated inside a protein globule with the surrounding electrolyte solution. The change of ion energy due to the intraglobular electric field preexisting in the enzyme molecule is calculated. Each of the factors listed above gives a large contribution into the ion energy in the case of Asp-102 these contributions compensate each other to a great extent.

Aspartic Acid↗