Femtosecond X-ray protein nanocrystallography

X-ray crystallography provides the vast majority of macromolecular structures, but the success of the method relies on growing crystals of sufficient size. In conventional measurements, the necessary increase in X-ray dose to record data from crystals that are too small leads to extensive damage before a diffraction signal can be recorded. It is particularly challenging to obtain large, well-diffracting crystals of membrane proteins, for which fewer than 300 unique structures have been determined despite their importance in all living cells. Here we present a method for structure determination where single-crystal X-ray diffraction 'snapshots' are collected from a fully hydrated stream of nanocrystals using femtosecond pulses from a hard-X-ray free-electron laser, the Linac Coherent Light Source. We prove this concept with nanocrystals of photosystem I, one of the largest membrane protein complexes. More than 3,000,000 diffraction patterns were collected in this study, and a three-dimensional data set was assembled from individual photosystem I nanocrystals (～200?nm to 2?μm in size). We mitigate the problem of radiation damage in crystallography by using pulses briefer than the timescale of most damage processes. This offers a new approach to structure determination of macromolecules that do not yield crystals of sufficient size for studies using conventional radiation sources or are particularly sensitive to radiation damage.     

Active immunotherapy of mouse RC 19 and E ♀ K1 leukaemias applied after the intravenous transplantation of the tumour cells

Résumé L'immunothérapie active non spécifique ou mixte, appliquée 24 h après la greffe isogénique de la leucémie RC 19, possède une action considérable; appliquée dans les mêmes conditions après la greffe de la leucémie E K1, elle possède une action modérée mais significative. Ces résultats confirment l'effet antileucémique de l'immunothérapie active appliquée après le début de la maladie et montre qu'elle est même efficace sur les cellules tumorales disséminées.

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This work has been carried out with the aid of INSERM, contract No. 66-235.     

Circles in spermatocyte chromatin loops. Electron microscopy and AgAs-NORs studies

Summary We describe the production of circles in chromomeric loops during the pachytene stage of the spermatocytes. These circles are found attached to chromatin or already free in the nucleoplasm. Each circle measures an average of 3700 Å in circunference. We suggest that such circles might indicate the presence of tandem repetitions.This work was supported by grants from Brazilian National Research Council-CNPq, Fundaçaó de Amparo à Pesquisa do Estado de S. Paulo-FAPESP and Instituto Butantan Research Found-FEDIB.We are grateful to Dr A. Brunner, Jr, for the permission to use the electron microscope.     

Fast and slow myosin within single skeletal muscle fibres of adult rabbits.

There is good evidence for the coexistence of different myosin types both in developing muscles and in Purkinje cells from adult chicken hearts. In skeletal muscle fibres of adult animals, however, coexistence of fast (FM) and slow (SM) myosin has only been demonstrated after long-term electrical stimulation. The term 'promiscuity' has recently been coined to describe the coexistence of different myosin isoenzymes within a single fibre. Using novel, refined immunological methods we demonstrate here the presence of both FM and SM within single fibres of the musculus tibialis anterior of adult rabbits. Essentially identical results were also obtained with other muscles. Our findings imply that the genes coding for FM and SM can be expressed simultaneously within the same cell throughout an animal's entire life, and not only during development or after artificial electrical stimulation.     

Depth perception by means of ambient sounds in a small mammal

Summary Golden hamsters placed on a jumping stand from which they can descend onto a shallow or deep landing platform prefer to descend on to the shallow platform, even when tested under IR-light without tactile cues. This preference disappears for subjects with plugged ears. The simultaneous recording of the animal's behaviour and possible emission of ultrasound as well as experiments in which the external acoustical conditions or the sound-reflecting properties of the jumping apparatus were altered suggest that the animals use certain parameters of the ambient sound field for depth perception. Acknowledgments. This research was supported by the Fonds National Suisse de la Recherche Scientifique, grant No. 3.349.74.     

Influence de différents types de diurèse sur l'excrétion rénale de l'urée étudiée chez le rat, à l'aide des microponctions rénales

Summary The renal tubular fate of urea, as studied in the rat by free-flow micropunctures of cortical tubules, is shown to vary with different types of diuresis (urea overloading, iso- or hypertonic saline diuresis). Under certain experimental conditions, the renal tubular handling of urea appears to differ in the cortical and the juxtamedullary nephrons.

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Ce travail bénéficie du soutien du Fond National suiss de la Recharche Scientifique (crédit Nos. 4495 et 4983).