Dissociation of heme-globin complexes by blackbody infrared radiative dissociation: molecular specificity in the gas phase?

The temperature dependence of the unimolecular kinetics for dissociation of the heme group from holo-myoglobin (Mb) and holo-hemoglobin alpha-chain (Hb-alpha) was investigated with blackbody infrared radiative dissociation (BIRD). The rate constant for dissociation of the 9 + charge state of Mb formed by electrospray ionization from a "pseudo-native" solution is 60% lower than that of Hb-alpha at each of the temperatures investigated. In solutions of pH 5.5-8.0, the thermal dissociation rate for Mb is also lower than that of HB-alpha (Hargrove, M. S. et al. J. Biol. Chem.1994, 269, 4207-4214). Thus, Mb is thermally more stable with respect to heme loss than Hb-alpha both in the gas phase and in solution. The Arrhenius activation parameters for both dissociation processes are indistinguishable within the current experimental error (activation energy 0.9 eV and pre-exponential factor of 10(8-10) s(-1)). The 9+ to 12+ charge states of Mb have similar Arrhenius parameters when these ions are formed from pseudo-native solutions. In contrast, the activation energies and pre-exponential factors decrease from 0.8 to 0.3 eV and 10(7) to 10(2) s(-1), respectively, for the 9 + to 12 + charge states formed from acidified solutions in which at least 50% of the secondary structure is lost. These results demonstrate that gas-phase Mb ions retain clear memory of the composition of the solution from which they are formed and that these differences can be probed by BIRD.

Effects of charge state on fragmentation pathways, dynamics, and activation energies of ubiquitin ions measured by blackbody infrared radiative dissociation

Blackbody infrared radiative dissociation spectra of the (M + 5H)5+ through (M + 11H)11+ ions of the protein ubiquitin (8.6 kDa) formed by electrospray ionization were measured in a Fourier-transform mass spectrometer. The 5+ ion dissociates exclusively by loss of water and/or ammonia, whereas the 11+ charge state dissociates only by formation of complementary y and b ions. These two processes are competitive for intermediate charge state ions, with the formation of y and b ions increasingly favored for the higher charge states. The y and b ions are formed by cleavage of the backbone amide bond on the C-terminal side of acidic residues exclusively, with cleavage adjacent to aspartic acid favored. Thermal unimolecular dissociation rate constants for the dissociation of each of these charge states were measured. From the temperature dependence of these rates, Arrhenius activation parameters in the rapid energy exchange limit are obtained. The activation energies (Ea) and preexponential factors (A) for the 5+, 8+, and 9+ ions are 1.2 eV and 10(12) s-1, respectively. These values for the 6+ and 7+ ions are 0.9-1.0 eV and 10(9) s-1, and those for the 10+ and 11+ ions are 1.6 eV and 10(16)-10(17) s-1. Thus, with the exception of the 5+ ion, the higher charge states of ubiquitin have larger dissociation activation energies than the lower charge states. The different A factors observed for production of y and b ions from different precursor charge states indicate that they are formed by different mechanisms, ranging from relatively complex rearrangements to direct bond cleavages. These results clearly demonstrate that the relative dissociation rates of large biomolecule ions by themselves are not necessarily a reliable indicator of their relative dissociation energies, even when similar fragment ions are formed.

Binding energies of the proton-bound amino Acid dimers gly.gly, ala.ala, gly.ala, and lys.lys measured by blackbody infrared radiative dissociation

Arrhenius activation energies in the zero-pressure limit for dissociation of gas-phase proton-bound homodimers of N,N-dimethylacetamide (N,N-DMA), glycine, alanine, and lysine and the heterodimer alanine.glycine were measured using blackbody infrared radiative dissociation (BIRD). In combination with master equation modeling of the kinetic data, binding energies of these dimers were determined. A value of 1.25 +/- 0.05 eV is obtained for N,N-DMA and is in excellent agreement with that reported in the literature. The value obtained from the truncated Boltzmann model is significantly higher, indicating that the assumptions of this model do not apply to these ions. This is due to the competitive rates of photon emission and dissociation for these relatively large ions. The binding energies of the amino acid dimers are ~1.15 +/- 0.05 eV and are indistinguishable despite the difference in their gas-phase basicity and structure. The threshold dissociation energies can be accurately modeled using a range of dissociation parameters and absorption/emission rates. However, the absolute values of the dissociation rates depend more strongly on the absorption/emission rates. For N,N-DMA and glycine, an accurate fit was obtained using frequencies and transition dipole moments calculated at the ab initio RHF/2-31G* and MP2/2-31G* level, respectively. In order to obtain a similar accuracy using values obtained from AM1 semiempirical calculations, it was necessary to multiply the transition dipole moments by a factor of 3. These results demonstrate that in combination with master equation modeling, BIRD can be used to obtain accurate threshold dissociation energies of relatively small ions of biological interest.

Unimolecular reaction kinetics in the high-pressure limit without collisions

Molecular activation by blackbody photons, first postulated in 1919 by Perrin, plays a dominant role in the unimolecular dissociation of large ions trapped at low pressure in a Fourier-transform mass spectrometer. Under readily achievable experimental conditions, molecular ions of the protein ubiquitin equilibrate with the blackbody radiation field inside the vacuum chamber. The internal energy of a population of these ions is given by a Boltzmann distribution. From the temperature dependence of unimolecular dissociation rate constants measured in the zero-pressure limit, Arrhenius activation parameters equal to those in the high-pressure limit are obtained.

Modeling the maximum charge state of arginine-containing Peptide ions formed by electrospray ionization

A model for the gas-phase proton transfer reactivity of multiply protonated molecules is used to quantitatively account for the maximum charge states of a series of arginine-containing peptide ions measured by Downard and Biemann (Int. J. Mass Spectrom. Ion Processes 1995, 148, 191-202). We find that our calculations account exactly for the maximum charge state for 7 of the 10 peptides and are off by one charge for the remaining 3. These calculations clearly predict the trend in maximum charge states for these peptides and provide further evidence that the maximum charge state of ions formed by electrospray ionization is determined by their gas-phase proton transfer reactivity.

Proton transfer reactivity of large multiply charged ions

Charge-charge interactions dramatically influence the dissociation and proton transfer reactivity of large multiply protonated ions. In combination with tandem mass spectrometry, proton transfer reactions have been used to determine the charge state of an ion and to increase the effective mass resolution of electrospray ionization mass spectra. A model for the proton transfer reactivity of multiply protonated ions, in which protons are assigned to specific sites in an ion based on the intrinsic reactivity of the site and the sum of point-charge Coulomb interactions between charges, is discussed. In combination with experimentally measured rates of proton transfer to bases of known gas-phase basicity, information about the intramolecular electrostatic interactions, gas-phase ion conformation and maximum charge state of an ion produced by electrospray ionization can be obtained.

Conformations and folding of lysozyme ions in vacuo

Proton transfer reactivity of isolated charge states of the protein hen egg-white lysozyme shows that multiple distinct conformations of this protein are stable in the gas phase. The reactivities of the 9+ and 10+ charge state ions, formed by electrospray ionization of "native" (disulfide-intact) and "denatured" (disulfide-reduced) solutions, are consistent with values calculated for ions in their crystal structure and fully denatured conformations, respectively. Charge states below 8+ of both forms, formed by proton stripping, have similar or indistinguishable reactivities, indicating that the disulfide-reduced ions fold in the gas phase to a more compact conformation.

On the maximum charge state and proton transfer reactivity of peptide and protein ions formed by electrospray ionization

A relatively simple model for calculation of the energetics of gas-phase proton transfer reactions and the maximum charge state of multiply protonated ions formed by electrospray ionization is presented. This model is based on estimates of the intrinsic proton transfer reactivity of sites of protonation and point charge Coulomb interactions. From this model, apparent gas-phase basicities (GB(app)) of multiply protonated ions are calculated. Comparison of this value to the gas-phase basicity of the solvent from which an ion is formed enables a maximum charge state to be calculated. For 13 commonly electrosprayed proteins, our calculated maximum charge states are within an average of 6% of the experimental values reported in the literature. This indicates that the maximum charge state for proteins is determined by their gas-phase reactivity. Similar results are observed for peptides with many basic residues. For peptides with few basic residues, we find that the maximum charge state is better correlated to the charge state in solution. For low charge state ions, we find that the most basic sites Arg, Lys, and His are preferentially protonated. A significant fraction of the less basic residues Pro, Trp, and Gln are protonated in high charge state ions. The calculated GB(app) of individual protonation sites varies dramatically in the high charge state ions. From these values, we calculate a reduced cross section for proton transfer reactivity that is significantly lower than the Langevin collision frequency when the GB(app) of the ion is approximately equal to the GB of the neutral base.

The social implications of lower urinary tract reconstruction performed during childhood

OBJECTIVE

To compare the social effects of urinary diversion, undiversion and orthotopic bladder reconstruction performed during childhood.

PATIENTS AND METHODS

Of 99 patients treated at the Wessex Centre for Paediatric Surgery between 1960 and 1993, 46 (16 with a urinary diversion, eight with an undiversion and 22 with bladder reconstruction) were interviewed using a standardized questionnaire. Information was collected about the types and results of surgery, the medical support received and the social effects of the different treatments.

RESULTS

By day, continence or only occasional wetting was achieved in 13 patients with diversions, all those with undiversions and 16 of those with reconstructions. At night, 13 patients with diversions, seven with undiversions and 18 with reconstructions were dry or only occasionally wet. Re-operation rates were higher in those with reconstruction and undiversion. Only five of the diversion group were satisfied with their management compared to all patients in the other two groups. The social effects in terms of employment, schooling, independence, body image and social interactions were also better in those with undiversions and reconstructions.

CONCLUSIONS

The social effects of undiversion and bladder reconstruction were better than those following urinary diversion despite the higher re-operation rates and the need for a rigid regimen of post-operative care. However, the need for continuing medical support in this group of patients cannot be over emphasized, and the vital role of the urological nurse specialist is stressed.

Hypervariable polymorphism of APO(a) in blacks and whites as reflected by phenotyping

Genetic polymorphism at the apolipoprotein(a) structural locus was investigated in 203 American blacks using a high-resolution SDS-agarose electrophoresis method followed by immunoblotting, and the gene frequency data were compared with a previously screened American white sample using the same method. Between the two samples, a total of 27 discrete APO(a) allelic isoforms have been documented; of these, 24 were common to both groups. Of the 203 blacks screened, APO(a) immunoreactive isoforms were detected in 201, with a total of 101 distinct phenotypes (67 (33%) single-banded and 134 (67%) double-banded). A similar level of gene diversity was observed at the APO(a) locus in blacks (93%) and whites (94%). Despite having a similar number of alleles and a similar level of gene diversity, the frequencies of some APO(a) alleles were significantly different between blacks and whites. Overall, the frequencies of large-size APO(a) alleles, associated with lower LP(a) levels, were significantly lower (P < 0.0001), while the frequencies of medium-size APO(a) alleles, associated with intermediate LP(a) levels, were significantly higher (P < 0.0001) in blacks than in whites. However, the frequencies of small-size alleles, associated with higher LP(a) levels, were comparable between the two race groups. These data indicate that the observed differences in mean LP(a) levels between whites and blacks may be accounted for by the size variation at the APO(a) structural locus.

Measuring the Electron's Charge and the Fine-Structure Constant by Counting Electrons on a Capacitor

The charge of the electron can be determined by simply placing a known number of electrons on one electrode of a capacitor and measuring the voltage, V_s, across the capacitor. If V_s is measured in terms of the Josephson volt and the capacitor is measured in SI units then the fine-structure constant is the quantity determined. Recent developments involving single electron tunneling, SET, have shown bow to count the electrons as well as how to make an electrometer with sufficient sensitivity to measure the charge.

Comparison of locations used in cotton-breeding trials

Cotton-breeding trials are conducted annually throughout the commercial growing regions of eastern Australia. Accumulated yield data for the period 1974-85 were assembled into an incomplete cultivar x location x year table. This table was then analysed in order to compare test locations. The method involved analysing cultivar x location tables separately for each year, using symmetric joint regression analysis. Results were then collected into location x year tables and further analysed. Four criteria for comparing test locations were developed. The discrimination criterion is important when locations are evaluated in terms of their ability to display cultivar differences. The representation criterion measures the ability of a location to mirror the relative performance of cultivars over all locations. The other 2 criteria are concerned with the mean yield at test locations and the stability of location yields over years. Based on the 4 criteria, preferred test locations are recommended.

Molecular basis of a unique African variant (A-IV 5) of human apolipoprotein A-IV and its significance in lipid metabolism

Human apolipoprotein A-IV (apoA-IV) exhibits a genetically determined structural polymorphism amenable to analysis by isoelectric focusing and immunoblotting techniques. We have determined the allele frequency and molecular basis of a unique ApoA-IV*5 allele which is widely distributed among blacks but is absent in other populations. The frequency of the ApoA-IV*5 allele in blacks (N = 308) was estimated to be 3.2%. In comparison to the common ApoA-IV*1 allele, analysis of coding and non-coding sequences of the ApoA-IV*5 allele revealed an in-frame insertion of 12 nucleotides near the carboxyl terminal region of the mature protein. The insertion involves an exact duplication of the second of the four repeats and codes for 4 amino acids glutamic acid (GAA), glutamine (CAG), glutamine (CAG), and glutamine (CAG) and is responsible for the charge shift of the the apoA-IV 5 isoform slightly toward the anode as compared to the wild type apoA-IV 1 isoform on the isoelectric focusing gel. This in-frame insertion occurs in a region which is highly conserved among rat, mouse, and humans. In addition to the 12 nucleotide insertion, the four individuals sequenced for the ApoA-IV*5 allele also revealed a same-sense mutation by replacing G to T at the third position of codon 316. Our preliminary data suggest that this unique black allele marker may be of potentially significance in studies of human lipid metabolism and in microevolution.

Irrigated plot trials in cotton: quantifying end effects and the influence of plot size upon intergenotypic competition

Individual rows of irrigated, multi-row plots in a cotton breeding trial were harvested, and seed cotton yields were measured. Intergenotypic competition had occurred between the neighbouring long sides of the oblong plots. A further trial was conducted to measure competition in three- and four-row plots and to establish which system gave the least biased genotype means for lint yield (kg/ ha). However, competition in this experiment was minimal and both systems gave comparable results. The effect of bare ground at the end of plots was investigated. When bare ground, as compared to a discarded border, was present during their growing season, then end plants, for seven out of eight genotypes, were larger and plot yields were inflated. These results provided no conclusive evidence that current practices for field trials with cotton should be changed.

High resolution and tandem fourier-transform mass spectrometry with californium-252 plasma desorption

For ions formed by plasma desorption (PD) in a Fourier-transform mass spectrometer, high resolution measurements are demonstrated, such as 65,000 (FWHH) for the protonated molecularion of gramicidin S (MW 1140.7). Resolution is substantially improved by delaying measurements until a significant ion concentration has built up in the cell, and by collisionally deactivating the orbital kinetic energy of the ions. This also makes the ions available for subsequent dissociation steps, so that tandem mass spectrometry can be demonstrated for PD ions. With this for larger ions, collisionally activated dissociation (CAD) is effected with > 85% efficiency. The CAD spectra of (M + Na)(+) and of fragment ions from the PD of gramicidin S provide structurally useful information.

Surface-induced dissociation of peptide ions in Fourier-transform mass spectrometry

Peptide molecular ion species up to m/z 3055 introduced into a Fourier-transform mass spectrometer can be made to undergo extensive fragmentation by electrically floating the ion cell. The proportion of ions dissociated increases with increasing voltage, with 48 eV producing the highest absolute abundance of fragment ions above m/z 200. At this energy, spectra closely resemble those from photodissociation at 193 nm, indicating an internal energy deposition of 6-7 eV; change of product abundances with kinetic energy resembles a conventional breakdown curve. The precursor ions apparently are electrostatically attracted to strike screen wires across the ion cell entrance, producing daughter ions of low kinetic energy.

193 nm Laser photoionization and photodissociation for isomer differentiation in Fourier-transform mass spectrometry

Energetic (6.4 eV) multiphoton ionization (MPI) or photodissociation, effected interchangeably in a Fourier-transform mass spectrometer, can differentiate isomers that yield similar electron ionization spectra. Selectivity is shown for isomers of C7H8, C7H9N, C7H7F, C8H10, but not of C6H3Cl{3} and C14H10. The contrasting MPI fragmentations and ionization efficiencies, as well as high sensitivities, are of substantial analytical utility. The high ionization efficiency makes possible high resolution MPI spectra, such as 470,000 (FWHH) for the molecular ion of anthracene, from a single laser pulse.

Efficiency of collisionally-activated dissociation and 193-nm photodissociation of peptide ions in fourier transform mass spectrometry

For tandem mass spectrometry, the Fourier transform instrument exhibits advantages for the use of collisionally-activated dissociation (CAD). The CAD energy deposited in larger ions can be greatly increased by extending the collision time to as much as 120 s, and the efficiency of trapping and measuring CAD product ions is many times greater than that found for triple-quadrupole or magnetic sector instruments, although the increased pressure from the collision gas is an offsetting disadvantage. A novel system that uses the same laser for photodesorption of ions and their subsequent photodissociation can produce complete dissociation of larger oligopeptide ions and unusually abundant fragment ions. In comparison to CAD, much more internal energy can be deposited in the primary ions using 193-nm photons, sufficient to dissociate peptide ions of m/z > 2000. Mass spectra closely resembling ion photodissociation spectra can also be obtained by' neutral photodissociation (193-nm laser irradiation of the sample) followed by ion photodesorption.

Hadamard transform measurement of tandem Fourier-transform mass spectra

The simultaneous collection of multiple spectra using tandem (MS/MS) and multidimensional (MS/MS/MS) mass spectrometry from multiple precursors is demonstrated to yield correspondingly enhanced sensitivity. This approach utilizes Hadamard transform deconvolution and takes advantage of the multichannel dissociation capability of Fourier-transform mass spectrometry. By application of this to an 11-component mixture, the 11 spectra of the products of dissociating 11 different combinations of six of the component molecular ions are measured; Hadamard transformation yields individual spectra of the precursor ions exhibiting a signal-to-noise improvement of 1.8x over spectra measured separately, as predicted by theory. Precursor ion selection with high specificity and product formation with high abundance reproducibility are critical; spurious peaks resulting from imperfect reproducibility can be minimized by using simultaneous equation coefficients reflecting the degree of precursor dissociation. Extension of this technique to MSn spectra is demonstrated with simultaneous MS/MS/MS monitoring of three precursors and three daughters yielding nine spectra representing the nine possible dissociation pathways. For MSn spectra, coding the product relationships for each additional step (e.g., precursor----daughter, daughter----granddaughter) requires elimination of half of the remaining ions. No ions are lost for coding in an improved Hadamard approach in which the combined daughter spectrum of the selected half of the precursors is subtracted from that of the other half.

Fourier-transform mass spectrometry of large molecules by electrospray ionization

The multiply charged ions produced by electrospray ionization of peptides of molecular masses up to 29 kDa have been successfully introduced into a Fourier transform mass spectrometer of unique capabilities for tandem mass spectrometry, large ion dissociation, and resolution. Electrospray ionization places an unusually high number of charges on a peptide yielding mass/charge (m/z) values of 600-1500; in this range at normal operating pressures (approximately 10(-9) torr; 1 torr = 133.3 Pa) Fourier-transform mass spectrometry resolving power is greater than 100,000. Although only 10(-7) torr pressure has been obtained with the initial interface, the resulting resolving power of 5000 makes possible the resolution of isotopic peaks of multiply charged ions. Mass measuring accuracies of a few daltons for molecular masses up to 17 kDa have also been achieved.

Regional evaluation of cotton cultivars in eastern Australia, 1974-85

In 1974, a district cotton cultivar trial was initiated to assess the yield and fibre quality of promising cultivars in all major Australian cotton growing areas over 1 or more years. A nearly 5-fold range in site yields (595-2451 kg/ha) occurred across locations and years. Yields were usually higher in the last 6 years of the trial (overall mean 1688 kg/ha) than in the first half (overall mean 1223 kg/ha). Queensland sites (except Theodore) were lower yielding than average, while New South Wales sites (except Warren) were higher yielding. Deltapine cultivars from the U.S.A. have been the dominant commercial cultivars during 1974-85, and in the first 9 years of the trials USA. or Australian-bred Deltapine types produced the highest overall lint yields. Since 1982, Australian-bred Siokra lines have been the highest yielding with their resistance to bacterial blight apparently being an important factor in their performance. The rate of genetic gain in lint yield, as assessed from the overall year means and the mean yield of the 2 control cultivars (Deltapine 16 and Namcala) grown in all 12 years of the trials, was 2.3% per year. These yield increases were also accompanied by improvements in fibre strength and micronaire value in some of the recently developed lines or cultivars. A number of genotypes with mutant traits associated with host plant resistance to insect pests were compared with their near-isogenic counterparts. Superokra leaf yielded 6% less than normal leaf, nectariless yielded similarly to nectaried, and glabrous yielded similarly to delta-smooth pubescence. Frego bract yielded less in 1 comparison but in 2 others was similar to the normal counterpart, while glabrous and frego bract together led to reduced yields. Intra-varietal selection was shown to produce useful gains in yield between 3 to 6.5%.

The use of uniformity data in the design and analysis of cotton and barley variety trials

The results of two uniformity trials, one in furrow-irrigated cotton, the other in barley, are presented and the yield data analysed. The two data sets, while both showing significant row and column effects, exhibited markedly different types of variation over the test area. The cotton data were more uniform and had stronger trends in columns and rows. There was a strong autocorrelation between plots in the barley data which was not evident in the cotton data. These results support the current preferences of cotton breeders for row and column designs and of barley breeders for neighbour designs when conducting variety trials in the field.