Ralph W. G. Wyckoff

THE ISOLATION OF TOBACCO RING SPOT AND OTHER VIRUS PROTEINS BY ULTRACENTRIFUGATION

A high molecular weight crystalline protein, possessing the properties of ring spot virus and differing markedly from tobacco mosaic virus protein in its physical, chemical and serological properties, has been isolated by means of an ultracentrifuge from Turkish tobacco plants diseased with tobacco ring spot virus. Ultracentrifugal methods were also used to demonstrate that high molecular weight proteins are characteristic of other virus diseases. The concentration of the different virus proteins in the host was found to differ greatly. The quantity ultracentrifuge, used in conjunction with an analytical ultracentrifuge, has proven to be a powerful tool for the concentration, purification and crystallization of high molecular weight virus proteins and to be indispensable in the case of unstable viruses existing in low concentration in the host.

X-Ray Diffraction Patterns from Reprecipitated Connective Tissue

For a number of years 1 it has been known that tendon gives excellent crystalline reflections. Recently 2 large spacings have been observed which provide strong evidence for the view that collagenous structures may be fibrous arrays of true crystals composed of very large molecules. Most forms of tendon from adult animals cannot be put into solution without obvious chemical disintegration. The work of Nageotte and of others 3 has, however, demonstrated that optically active fibrous precipitates can be obtained from weakly acid solutions made from the tail tendon of adult rats and from many connective tissues of foetal animals. The optical appearance of these precipitates suggests that they are at least similar to the tissue from which they were dissolved. We have carried out a series of experiments to determine: (a) whether reprecipitated tendon is really crystalline and (b) whether its X-ray diffraction pattern is like that of the original tissue. Reprecipitated connective tissue was obtained according to the procedures outlined by Nageotte. Pieces of freshly excised tail tendon from adult rats were placed in dilute (1 to 25,000) acetic acid. In such acid the tendon swells and a portion of it dissolves to form a clear but highly viscous solution. The reprecipitated tissue is obtained from this solution by salting out with 5% NaCl. Series of X-ray diffraction studies have been made of a number of these preparations. Some of these diffraction photographs were made with the usual short crystal-to-film distances; others were made with very small slit systems and with the large camera radii needed to record spacings of the order of 100 A.

Improvements in the Air‐Driven Ultracentrifuge for Molecular Sedimentation

A description is given of the following improvements in an air‐driven ultracentrifuge intended for molecular sedimentation: (1) A driving mechanism equipped (A) with reversing air jets that provide for smooth and rapid stopping and (B) with spring compression screws for adjustment to eliminate vibrations. (2) A head which makes it possible to centrifuge considerable volumes of solution in a field sufficiently great to concentrate and crystallize large protein molecules. (3) The use of a high pressure mercury arc in place of the usual direct‐current lamp as light source for both absorption and refractive index measurements. (4) A device for automatically taking the series of photographs needed for determinations of rate of sedimentation.

Ultracentrifugal Concentration of a Homogeneous Heavy Component from Tissues Diseased with Equine Encephalomyelitis

With the demonstration of the existence of a heavy protein in plant tissues diseased with tobacco mosaic virus 1 it became inevitable that similar proteins should be sought in other kinds of virus-infected tissues. Most viruses are more or less unstable towards the chemicals which would naturally be used in efforts to concentrate and purify them. The air-ultracentrifuge 2 has, however, furnished a new tool 3 which has been successful in extracting and purifying several of the less stable virus proteins causing plant diseases 4 and in preparing a similar substance 5 from virus-induced rabbit papillomas (Shope). The same type of ultracentrifugal examination has now been made of tissues diseased with the virus of equine encephalomyelitis.∗ As in the previous ultracentrifugal concentrations an angle-centrifuged tissue suspension was ultracentrifuged for one to one and a half hours in a maximum field of ca 50,000 times gravity. All but a trace of the virus activity was thus sedimented. The translucent pellet formed at the bottom of the tube by this ultracentrifugation was resuspended in a suitable solvent and the aggregated colloidal matter thrown down by another low speed centrifugation. Ultracentrifugation of this solution furnished a smaller but cleaner pellet. On occasion the purification of this pellet was carried further by a repetition of the cycle of centrifugation, ultracentrifugation and resuspension. The virus of equine encephalomyelitis is not thermostable; it rapidly becomes non-infectious at room temperature and cannot be relied upon to preserve its activity for long periods of time in the icebox. Therefore all manipulations, including the ultra-centrifugations, were carried out without delay and in the cold. Both the original suspensions and those resulting from the ultra-centrifugations were examined with an analytical ultracentrifuge arranged for photography according to the classical absorption method of Svedberg.

Light Metal Rotors for the Molecular Ultracentrifuge

Tests have been made of the range of usefulness of light metal rotors in the ultracentrifuge for molecular sedimentation. These experiments prove that duralumin 14 ST is definitely superior to the other alloys tested. They also indicate a shape of seven‐inch diameter rotor which if made of 14 ST can safely be used for centrifuging at speeds up to 900 r.p.s. (field at center of cell = 215,000 times gravity). For much more intense fields special steels must be used or the rotor diameter reduced.

The Effects of X-rays, Cathode, and Ultra-violet Rays on Yeast

Introduction THE following experiments, which form part of a series of quantitative studies of the action of radiation upon simple cells, are intended as a preliminary investigation of the way high velocity electrons, soft X-rays and ultra-violet light destroy yeast. Besides early observations1 of a qualitative character, some quantitative measurements2 bearing upon this problem have recently been described. In so far as they can be compared, our data, which were at hand before these others appeared, are in substantial agreement with them. Technic A parent culture of Saccharomyces cerevisiae (Variety 40) was obtained from the Fleischmann Laboratory. Transplants upon Naegelis agar medium were carried fifteen days before use in order to bring the cells to a resting stage. Cultures, prepared by spreading a suspension in NaCl of these resting cells upon the surface of the agar medium, were irradiated as soon as dry. After incubation for 24 hours at 22° C. the numbers of single cells and of groups of 2, 3–4, 5...

A Simple Self-rectifying Gas X-ray Tube

THIS tube was originally developed because of the need in some biological experiments for a constant and more intense source than is given by the commercially available X-ray tubes. It has proved to be so simple and reliable in everyday operation, however, that in this laboratory it has replaced commercial tubes for the preparation of the different kinds of photographs used in crystal analysis. Self-rectifying gas tubes have been made familiar to many through the Shearer tube, as manufactured by the firm of Adam Hilger. There is, however, a wide range of tube dimensions over which self-rectification can be obtained. The amount of high voltage current which a tube will pass unilaterally depends upon its total volume, the size of its cathode, the shape and size of the anode end and other details of its design. A number of forms have been made and tried out in this laboratory. The one to be described is undoubtedly not the best possible, but it has fulfilled our requirements sufficiently well to make further...

IX. Die Kristallstruktur von β-Cristobalit SiO2 (bei hohen Temperaturen stabile Form)

Einleitung. /S-Gristobalit ist die zwischen U 7 0 ° u n d 1710° G stabile Form) von kristallinem Siliziumdioxyd. Sie hält sich bis herab zu Temperaturen von etwa 230° G. In der Nähe dieses Punktes tritt eine Umwandlung in die zu niedrigeren Temperaturen gehörende a-Cristobalitmodifikation ein. Merkwürdigerweise liegt die Umwandlungstemperatur zwischen der ßund α-Form nicht ganz fest, sondern hängt von der thermischen Vorgeschichte des betreffenden Kristalls ab. Stellt man Cristobalit bei sehr hohen Temperaturen dar, so liegt der Umwandlungspunkt für β a bei etwa 240°, für a + ß bei etwa 270° C; für Gristobalite, die bei niederen Temperaturen entstanden sind, liegen die entsprechenden Punkte bis herab zu 198° bzw. 220° C. Die Symmetrie des Gristobalits bei Zimmertemperatur ist unbekannt. Die /i-Form hingegen soll kubisch sein. Sie ist optisch isotrop) und an einigen mangelhaft entwickelten Kristallen wurden die im kubischen System zu erwartenden Flächen nachgewiesen). Aus diesem Grunde schien es aussichtsvoller, eine volle Strukturbestimmung von /?-Cristobalit zu erhalten, als von irgendeiner der anderen kristallinen Modifikationen von SiOi, und dies gab den Grund zur vorliegenden Untersuchung ab.

The electron micrography of plant virus-antibody mixtures.

Summary Shadowed electron micrographs of mixtures of purified southern bean mosaic and bushy stunt viruses with their specific antisera show their spherical elementary bodies aggregated into microflocs in which the particle-separations seem to be about twice their normal values. More detailed electron micrographic study of these systems is underway.

The Crystal Structure of Thiourea

Sound knowledge of the atomic arrangements in crystals of the more important and complex organic Compounds can be gained only after a thorough study of several simple aliphatic and aromatic substances. The following determination of the structure of thiourea, as one of these simple Compounds, is interesting partly for itself and partly for the understanding it gives of some of the difficulties encountered when quantitative X-ray data are sought from organic crystals. Two previous investigations^) agree in finding four molecules of (NH2)20S in a unit cell based on the space group and having the approximate dimensions üo = 5.50 Ä, bo = 7.68 A, c^ = 8.57 Ä.