Validation of the Welch Allyn 'Vital Signs' blood pressure measurement device in pregnancy and pre-eclampsia.

OBJECTIVE: To establish the accuracy the Welch Allyn 'Vital Signs' blood pressure monitor in pregnancy and pre-eclampsia according to a modified British Hypertension Society protocol. DESIGN: Prospective observational study. SETTING: Maternity Unit/Obstetric Ward, Guy's and St Thomas' Hospital, London, UK. POPULATION: Forty-three pregnant women of whom 12 had pre-eclampsia. METHODS: Nine sequential same-arm measurements were taken from each woman by two trained observers, alternating between a mercury sphygmomanometer and the device. The last seven readings were analysed according to the British Hypertension Society protocol. The accuracy of the device was determined using the grading scale indicated by the British Hypertension Society protocol (grade A/B = pass, grade C/D = fail). MAIN OUTCOME MEASURES: Grading criteria of the British Hypertension Society Protocol. RESULTS: The Welch Allyn 'Vital Signs' monitor achieved a grade A for both systolic and diastolic pressures in pregnant women who did not have pre-eclampsia. In those women with pre-eclampsia, it achieved a grade D and B for systolic and diastolic pressures, respectively. The mean differences between the observers and the device in women without pre-eclampsia were -2.6 (6.4) and -1.5 (7.2) mmHg for systolic and diastolic pressures [and in pre-eclamptic women -7.8 (6.3) and -5.5 (6.5)mmHg]. It therefore fulfils criteria set by the Association for the Advancement of Medical Instrumentation (mean <5 mmHg and standard deviation <8 mmHg) in pregnancy, but not in pre-eclampsia. CONCLUSION: This is the first automated device suitable for robust clinical use that can be recommended for use in pregnancy. However, it should be borne in mind that-similar to other devices--it significantly under--recorded readings obtained in pre-eclamptic women.

Coulombic interactions between partially charged main-chain atoms not hydrogen-bonded to each other influence the conformations of alpha-helices and antiparallel beta-sheet. A new method for analysing the forces between hydrogen bonding groups in proteins includes all the Coulombic interactions.

An angle named gamma has been employed to describe the geometry at a hydrogen bond between main-chain atoms of polypeptides. In antiparallel beta-sheet, gamma is normally positive, whereas, in parallel beta-sheet and alpha-helices, it is negative. Although intriguing, no particular explanation has been offered to explain this result. We provide evidence that, in each case, the angular preference maximises the favourable Coulombic interaction between the partial negative charge on the carbonyl oxygen atom and the partial positive charge on the carbonyl carbon atom adjacent to the NH group to which it is hydrogen-bonded. Analyses of helices and beta-sheets in native proteins using Lennard-Jones potentials suggest that these carbonyl-carbonyl interactions are significant components of the attractive forces holding main-chain CONH groups together and are even in some cases larger than the hydrogen bonds themselves. A novel technique for analysing the forces holding together hydrogen-bonding groups in proteins is presented. It can be regarded as a development of the Kabsch and Sander method of calculating the energy of hydrogen bonds between main-chain atoms. In their program, electrostatic interactions are calculated between appropriate pairs of atoms, i.e. NH binding to CO. Instead, in our method, the four N, H, C, and O atoms, in a peptide bond are taken as a unit and the interaction between two NHCO groups calculated. We also use a Lennard-Jones potential, rather than just measuring the Coulombic interaction. With this approach, account is taken of all types of interactions between partially charged atoms, not only the hydrogen bonds.

Coulombic attractions between partially charged main-chain atoms stabilise the right-handed twist found in most beta-strands.

The use of Lennard-Jones potentials gives rise to an expected energy distribution for main-chain polypeptide conformations in the Ramachandran plot that matches well the observed distribution of phi, psi values in high-resolution proteins. The position of the energy minimum in the beta-strand conformation region is situated where there is a substantial contribution from the electrostatic attraction between the partial charge of the carbonyl carbon atom of one amino acid residue and that of the carbonyl oxygen atom of an adjacent residue. This attraction gives rise to a preference for the right-twisted beta-strand conformation compared with the left-twisted conformation. The majority of beta-sheets are twisted, almost always in one direction. Looking along a single strand, the twist is to the right. This twist also helps provide a rationale for the characteristic topology of the strand-helix-strand unit often observed in alpha/beta proteins. The electrostatic explanation for the twist we propose has not, to our knowledge, been explicitly suggested previously. The factor that has been most widely proposed to explain the twist is steric hindrance involving side-chain atoms. We provide evidence that the electrostatic effect is of comparable significance. Right-twisted beta-strands are geometrically closely related to polyproline II helices and to collagen helices, both of which are left-handed. Short regions of polyproline II type helices, which are sometimes, but not always, rich in proline residues, are common at protein surfaces. We point out that these helices are stabilised by the same carbonyl-carbonyl interactions as in right-twisted beta-strands.

Common ring motifs in proteins involving asparagine or glutamine amide groups hydrogen-bonded to main-chain atoms.

We report the frequent occurrence in proteins of motifs consisting of either 9-membered or 11-membered rings that involve the side-chain amide groups of asparagine and glutamine residues. The syn CO and NH groups of these amide groups are hydrogen-bonded to the main-chain NH and CO groups of other amino acid residues. The main-chain part of both the 9-membered and 11-membered rings has the conformation of a beta-strand. One such ring motifs occurs, on average, in half of all the proteins we examined. Similar conformations are found for most examples of the 9-membered and 11-membered rings. One of the 11-membered rings is distinct, compared to the others, in that its main-chain part has a mirror-image conformation. Another of the 11-membered rings occurs at the interior of the variable domains of some antibodies and assists in linking the two beta-sheets. We observe one 9-membered ring structure in a dihydrofolate reductase complex in which the amide in the nicotinamide group of the ligand NADP is bound to the enzyme. Groups that can form hydrogen bonds in a similar way to amide groups occur in several nucleotide bases; we find one example of a 9-membered ring involving adenine and main-chain atoms in the FAD-protein complex of glutathione reductase. Both have conformations like those of the other 9-membered rings.

Displaying inter-main chain hydrogen bond patterns in proteins.

Two computer graphics techniques for displaying hydrogen bonds between the main chains of different proteins are described, and illustrated for two thiol proteases. (The X-ray crystallography was performed by Kamphuis et al. in 1984, and by Baker and Dodson in 1980.) One is a three-dimensional model that can be manipulated in space; the hydrogen bonds are represented with the smoothed alpha-carbon plot of the polypeptide chain. In the other type of display, hydrogen bonds are viewed in relation to the one-dimensional sequence. Both types of picture facilitate visualization of hydrogen bond patterns, such that loop motifs, as well as alpha-helices and beta-sheets, can be examined easily. We suggest that such displays are useful as a general means of displaying whole proteins and whole domains because they reveal more information than do conventional simplified pictures of proteins, which focus exclusively on alpha-helices and beta-sheets. These techniques can be implemented on a UNIX-based computer graphics workstation. (UNIX is a trademark of Bell Telephone laboratories.)

One type of gamma-turn, rather than the other gives rise to chain-reversal in proteins.

Gamma-turns may be defined by a hydrogen bond between the carbonyl group of one amino acid residue and the amino group of the acid two residues ahead in the sequence. They occur as two types, inverse gamma-turns and classic gamma-turns (classic gamma-turns are usually called just gamma-turns but we prefer to add the adjective classic to distinguish them from the word gamma-turn, referring collectively to both). Of the two, classic gamma-turns are less common and are considered by all authors to be extreme rarities in proteins. However, we find that a number do occur in a sample of proteins of known three-dimensional structure. One occurs at the edge of the second hypervariable region of the light chain in some immunoglobulins. All classic gamma-turns except one are associated with a reversal in the main chain direction. In most cases, the turn lies at the loop end of a beta-hairpin. By contrast, inverse gamma-turns, although giving rise to a kink in the chain, rarely occur within beta-hairpins and are seldom situated at a position of reversal, by 180 degrees, in chain direction.

Four classes of beta-hairpins in proteins.

We show that beta-hairpins can be divided into four classes, each with a number of members. Hairpins from a single class are readily interconverted by loss or gain of hydrogen bonds, but interconversion between classes requires complete unzipping and reformation of the entire beta-hairpin. Sibanda & Thornton [(1985) Nature (London) 316, 170-174] have classified beta-hairpins as either two-residue, three-residue, four-residue etc., loops. We point out that their nomenclature, by itself, gives rise to ambiguities, but that, if the class (one of the four mentioned above) is also specified, the description of beta-hairpins becomes straightforward. A range of proteins of known three-dimensional structure has been examined; it provides examples of hairpins of each of the four classes and give some indication of their frequency of occurrence. The distribution observed is substantially different from that described by Sibanda & Thornton [(1985) Nature (London) 316, 170-174].

Sequential electrochemical reduction, solvent partition, and automated thiol colorimetry for urinary captopril and its disulfides.

Analysis of urinary captopril was necessary for dosage form bioavailability and dose titration studies. The necessity for long-term storage of samples prior to analysis and the presence of an oxidation-prone thiol of captopril required development of an acid-chelate stabilization method for urinary captopril. An electrochemical reduction released disulfide-conjugated captopril for thiol colorimetry. Of several rugged reduction cells evaluated, one with a porous glass disk separating the anode and the mercury pool cathode was preferred. Methylene chloride partitions from acidified salt-saturated urines, before and after reduction, allowed the measurement of free and disulfide-conjugated captopril. The drug partitioned into the solvent, whereas the aqueous phase retained acid protonated, amino group-bearing thiols like cystine. Subsequent solvent evaporation volatilized other potential colorimetric interferences. An automated thiol colorimetry of 25 samples/hr was developed for analysis of the aqueous reconstitutes. Results were confirmed by a subsequently developed HPLC method with electrochemical detection.

High-pressure liquid chromatography of nadolol and other beta-adrenergic blocking drugs.

A high-pressure liquid chromatographic assay was developed for the analysis of the beta-adrenergic blocking agent nadolol as a bulk material or formulated in a tablet. Other beta-adrenergic blocking drugs such as acebutolol, alprenolol, atenolol, metoprolol, oxprenolol, pindolol, practolol, propranolol, sotalol, and timolol can be chromatographed in this system. An ethylsilane column and a mobile phase consisting of 35% methanol-65% aqueous 0.0005 M hydrochloric acid-0.05 M sodium chloride are used. Detection is either at 254 nm with a variable-wavelength detector. As exemplified by nadolol, the drug content can be quantitated with or without atenolol as an internal standard.