Tests of an asymmetric monochromator to provide increased flux on a synchrotron radiation beamline

Asymmetric channel-cut monochromators have been tested at the SRS. Results from both focused and unfocused beamlines have shown a threefold improvement in flux when compared with the flux obtained from a symmetric cut Si(111) monochromator. Some problems with using such monochromators and possible modifications are described.

Matching electrostatic charge between DNA and coat protein in filamentous bacteriophage. Fibre diffraction of charge-deletion mutants

The virion of Ff (fd, f1, M13) filamentous bacteriophage consists of a long tube of coat protein subunits in a shingled, helical array, surrounding a genome of circular single-stranded DNA. Modified fd virions have been generated by a mutation (K48A) that removes one positive charge from each coat protein subunit in the C-terminal region of the polypeptide chain facing the DNA. The number of nucleotides in the mutant DNA is unchanged, but the K48A virions are 35% longer than wild-type. We have measured the X-ray diffraction attributable to single virions in hydrated gels of wild-type and K48A bacteriophages. Most of the diffraction pattern shows no significant difference between wild-type and K48A. Since the DNA is only about 12% by weight of the wild-type virion, the diffraction pattern is dominated by the protein contribution, and the absence of significant differences indicates that there are no significant changes in the symmetry or structure of the protein coat. But there is a change in the diffraction pattern in a region where the DNA and protein contributions are comparable. The diffraction pattern of the K48A mutant shows an increase in intensity of one of the weaker equatorial peaks, relative to wild-type, in a region where the protein contribution has negative sign but the DNA contribution has positive sign. This is consistent with a decrease in the ratio of DNA:protein per unit length of the K48A mutant. The results support the view that the protein forms a sheath lined with positive charges interacting electrostatically and non-specifically with a negatively charged DNA core of matching charge density. The lower positive charge density lining the capsid in the K48A mutant means that correspondingly fewer nucleotides can be packaged per coat protein subunit, which in turn requires an elongation of the DNA inside the virion. A longer virion is thus required to package the same amount of DNA. Within the error of measurement, the number of positive charges on the protein interacting with the DNA is the same in K48A as in the wild-type, despite the fact that the mutant is 35% longer than the wild-type.

Radiation damage in protein crystals at low temperature

This paper describes the study of the effects of radiation damage on the quality of data collected from a protein crystal at 100 K. It is shown that radiation damage causes measurable effects in the diffraction pattern. This implies that, even at liquid nitrogen temperatures, there is a limit to the size of a crystal from which a complete data set can be collected.

[Infectious endocarditis in dentistry practice: recent controversies and modes of the use of antibiotic prophylaxis]

A survey by questionnaire to assess the daily practice of the antibiotic prophylaxis of infective endocarditis by physicians attending post-graduate schools of the Institutes of Oral Surgery and Stomatology (Group A n = 83) and Cardiology (Group B n = 46) of the Second University of Naples has been conducted. They were asked about dental procedure and cardiopathies that require prophylaxis for infective endocarditis, the relationship between infective endocarditis and rheumatic disease and the provision of antibiotic. Extraction of tooth and dental and oral surgery have been reported as the most risky procedures. Moreover provision of antibiotic prophylaxis was suggested to patients not at risk (pacemaker or coronary artery bypass), and was not suggested in high risk conditions (mitral valve prolapse with regurgitation and hypertrophic cardiomyopathy). Most of the 50-60% practitioners usually start the prophylaxis 24-48 hours before the procedure and prolong it for 48-72 hours. These results underline the need for improvement of the knowledge for the antibiotic prophylaxis of infective endocarditis.

[Surgical treatment of incessant atrial tachycardia: description of a case]

A 50 year old woman with no evidence of structural heart disease was referred for ectopic incessant repetitive atrial tachycardia uncontrolled by medical therapy. Intracavitary and transesophageal simultaneous recordings revealed the earliest atrial electrical activity to be located in the left atrium. Intraoperative electrophysiologic mapping demonstrated that the site of earliest atrial activation was in a small diverticulum of the left atrial appendage. Excision of the appendage and isolation of left atrium was carried out with restoration of sinus rhythm. The patient was arrhythmia-free till 24 months later. Surgical treatment appears to be an effective therapeutic option for drug-resistant ectopic atrial tachycardia.

[Double ventricular response to a single atrial stimulation caused by simultaneous anterograde conduction through two atrioventricular nodal pathways]

In a patient with atrioventricular nodal reentrant tachycardia, during programmed stimulation, an atrial extrastimulus induced a double ventricular response due to a single atrial depolarization, with simultaneous and delayed anterograde conduction through fast and slow pathways, and induced the tachycardia. Pacing-induced type I block involving both pathways put these pathways out of phase, so that the distal conduction system and the ventricle responded to both the fast and slow pathways anterograde impulses.

Molecular models and structural comparisons of native and mutant class I filamentous bacteriophages Ff (fd, f1, M13), If1 and IKe

The filamentous bacteriophages are flexible rods about 1 to 2 microns long and 6 nm in diameter, with a helical shell of protein subunits surrounding a DNA core. The approximately 50-residue coat protein subunit is largely alpha-helix and the axis of the alpha-helix makes a small angle with the axis of the virion. The protein shell can be considered in three sections: the outer surface, occupied by the N-terminal region of the subunit, rich in acidic residues that interact with the surrounding solvent and give the virion a low isoelectric point; the interior of the shell, including a 19-residue stretch of apolar side-chains, where protein subunits interact mainly with each other; and the inner surface, occupied by the C-terminal region of the subunit, rich in basic residues that interact with the DNA core. The fact that virtually all protein side-chain interactions are between different subunits in the coat protein array, rather than within subunits, makes this a useful model system for studies of interactions between alpha-helix subunits in a macromolecular assembly. We describe molecular models of the class I filamentous bacteriophages. This class includes strains fd, f1, M13 (these 3 very similar strains are members of the Ff group), If1 and IKe. Our model of fd has been refined to fit quantitative X-ray fibre diffraction data to 30 A resolution in the meridional direction and 7 A resolution in the equatorial direction. A simulated 3.3 A resolution diffraction pattern from this model has the same general distribution of intensity as the experimental diffraction pattern. The observed diffraction data at 7 A resolution are fitted much better by the calculated diffraction pattern of our molecular model than by that of a model in which the alpha-helix subunit is represented by a rod of uniform density. The fact that our fd model explains the fd diffraction data is only part of our structure analysis. The atomic details of the model are supported by non-diffraction data, in part previously published and in part newly reported here. These data include information about permitted or forbidden side-chain replacements, about the effect of chemical modification, and about spectroscopic experiments.(ABSTRACT TRUNCATED AT 400 WORDS)

[Linking in a phase-3 branch block: the electrocardiographic manifestations]

Two cases of phase 3 intraventricular block and linking phenomenon of type 1 and type 2 (or bigeminal rhythm linking) are presented. In the first case, complexes that follow the extrasystolic blocked beat are wide, although they are associated with relative long R-R cycle:type 1 linking. In the second case, bundle branch block and normal conduction alternate in bigeminal extrasystolic beats:type 2 linking. The linking phenomenon is due to concealed retrograde penetration of the bundle branch that is blocked in anterograde direction. It delays the cycle and the refractory period of the bundle branch. Therefore, in type 1 linking, the subsequent stimulus, although occurring with a long R-R cycle, is again blocked in the same bundle branch. In type 2 linking, the R-R cycle and refractory period, occurring after bundle branch block, are shorted because comprised between retrograde activation by extrastimulus and anterograde activation by subsequent sinus stimulus. The subsequent ectopic impulse, although premature, is normally conducted.

[Slow and fast AV nodal pathways in tachycardia complicating Wolff-Parkinson-White syndrome: report of a case]

Electrophysiologic studies in a patient with intermittent ventricular pre-excitation revealed several types of paroxysmal narrow-QRS tachycardia (PSVT). One type of PSVT was characterized by normal retrograde atrial sequences with P waves occurring simultaneously with QRS. This type of PSVT reflected AV nodal reentry with anterograde slow pathway and retrograde fast pathway conduction. A second PSVT reflected alternation of anterograde fast and slow AV nodal pathway conduction and retrograde anomalous pathway conduction. A third PSVT reflected anterograde slow AV nodal pathway and retrograde anomalous pathway conduction. Moreover, discontinuous AV nodal conduction curves (A1A2/H1H2), characteristic of dual AV nodal pathway conduction, were obtained with programmed atrial extra stimulation. These observations suggest that dual AV nodal pathway conduction can coexist with abnormal bypass tract and can be the cause of PSVT in patients with Wolff-Parkinson-White syndrome.

[Electric alternans of QRS: its electrophysiologic significance in narrow QRS supraventricular paroxysmal tachycardia]

The results of 22 patient's transesophageal electrophysiologic studies were analyzed to value the meaning of QRS alternans during narrow QRS tachycardia. Standard ECG showed ventricular pre-excitation in eight patients. QRS alternans were in six of them: heart rate was included between 230 and 374 m/sec (301.8 +/- 42 m/sec); in the remaining 16 patients, heart rate was included between 240 and 450 m/sec (350.0 +/- 42 m/sec). Our findings suggest that QRS alternans is related to the rate of tachycardia rather than to the presence of an accessory pathway.

[Phase 3 and phase 4 bundle of branch block]

Intermittent left bundle branch blocks are present in the ECGs of 1 patient with mitral valve disease. By occurring either after short or long cycles they represent respectively phase 3 and phase 4 blocks. Such mechanisms emphasize the relationship between automatism and conduction. The occurrence of block and of normal conduction during cycles of the same length, its correlation with the conduction of the previous cycle, demonstrate the presence of a functional linking between successive impulses. This linking may occur every time a potential or active macroreentry circuit exist. In our case the circuit is formed by the 2 bundle branches which join distally in the ventricular septum.

[Ergometric test in the diagnostic and prognostic evaluation of arrhythmia]

One thousand three hundred patient's stress tests were analyzed to value arrhythmia outline and its relationship with anamnesis and clinical data. The patients were divided into two groups: group A, with no arrhythmias at rest, and group B with arrhythmias at rest. All classic nosographic arrhythmias were considered. In some teenager patients with arrhythmias at rest and no organic cardiopathy, anomalies disappeared during stress, showing the benignity of the phenomenon. Supraventricular stress induced arrhythmias has 1.2% of incidence in normal subjects, but 81% in heart disease patients. Supraventricular tachycardia was induced in 6 patients. Ventricular stress induced arrhythmias are found in 4.9%. Two cases of sudden death occurred in our groups.

[Permanent atrial standstill and atrial disease]

A case of permanent atrial standstill suspected upon electrocardiogram is reported, and confirmed by electrophysiological investigation. The originality of this case resides in the fact that the atrial standstill marks the developmental outcome of a bradycardia-tachycardia syndrome. This developmental sequence is the subject on discussion. It is concluded that a combination of auricular muscle lesion and sinus node tissue remains the most plausible anatomical and pathophysiological substratum of the bradycardia-tachycardia syndrome which developed into atrial standstill.

[EGG and arrhythmia in subjects with implanted dual-chamber VDD and DDD pacemakers]

The ECGs of four patients with implanted dual chamber VDD and DDD PMKs are shown to demonstrate the difficulty of their interpretation and show some arrhythmias related to dual chamber pacing. In the first patient the DDD PMK caused a high ventricular frequency synchronizing on the atrial fibrillation "f" waves which occurred suddenly some time after PMK implantation; this problem was solved by programming the PMK in VVI. The second and third case, with implanted DDD and VDD PMK respectively, exemplify atrial sensing dysfunction due to atrial catheter displacement. In the fourth patient, with implanted VDD PMK, VDD stimulation periods and VVI ones alternated due to non-adjusted programming. Therefore, the paper re-emphasizes the need for accurate and periodic controls of patients with implanted PMK to correct dysfunction or undesirable patterns of stimulation.

X-ray diffraction evidence for the existence of 102.0- and 230.0-nm transverse periodicities in striated muscle

Synchrotron radiation techniques have enabled us to record meridional x-ray diffraction patterns from frog sartorius muscle at resolutions ranging from approximately 2,800 to 38 nm (i.e., overlapping with the optical microscope and the region normally accessible with low angle diffraction cameras). These diffraction patterns represent the transform of the low resolution structure of muscle projected on the sarcomere axis and sampled by its repeat. Altering the sarcomere length results in the sampling of different parts of this transform, which induces changes in the positions and the integrated intensities of the diffraction maxima. This effect has been used to determine the transform of the mass projection on the muscle axis in a quasicontinuous fashion. The results reveal the existence of maxima arising from long-range periodicities in the structure. Determination of the zeroes in the transforms has been used to obtain phase information from which electron density maps have been calculated. The x-ray diffraction diagrams and the resulting electron density maps show the existence of a series of mass bands, disposed transversely to the sarcomere axis and distributed at regular intervals. A set of these transverse structures is associated with thin filaments, and their 102.0-nm repeat suggests a close structural relationship with their known molecular components. A second set, spaced by approximately 230.0 nm, is also present; from diffraction theory one has to conclude that this repeat simultaneously exists in thick and thin filament regions.

The information available from anomalous scattering on fibres at different wavelengths

The contribution of a particular atom in a molecule to the total X-ray scattering can be altered by varying the wavelength in the region of the absorption edge of the atom. It is shown that only the changes in the real part of the anomalous scattering of the atom provide significant changes in a pattern from a fibre containing molecules with helical symmetry. Changes due to the imaginary component are small and Friedel differences cannot be observed, owing to the fibre disorder. The information which can be obtained is equivalent to that given by a truly isomorphous heavy-atom derivative. For the general case this is not sufficient to provide unambiguous phase information. If a twofold axis is present at right angles to the fibre axis then the amplitudes are real and the phase problem can, in favourable cases, be solved.

The solution conformations of the subclasses of human IgG deduced from sedimentation and small angle X-ray scattering studies

The solution conformations of human immunoglobulin G subclass molecules have been investigated by sedimentation and small-angle X-ray scattering techniques. Both methods qualitatively indicate IgG3 to be an extended molecule relative to IgG1. Sedimentation data have been collected for a number of paraproteins of all four subclasses and the hinge-deleted IgG1Dob protein. The known crystal structure of Dob allows the use of this protein as a basis for the proposal of models of the average conformations of IgG subclasses which are consistent with experimental s(0)20,w values. IgG1 is suggested to have a hinge length of 0-15 A and non-coplanar Fab arms; IgG2 to be effectively hingeless with folded-back Fab arms; IgG3 to have an extended hinge of the order of 100 A and IgG4 to be effectively hingeless and T-shaped. The possible correlation of these conformations with subclass function is discussed.