Max A. Lauffer

Entropy-driven processes in biology.

entropy-driven processes in biology , entropy-driven processes in biology , کتابخانه دیجیتالی دانشگاه علوم پزشکی و خدمات درمانی شهید بهشتی

Functions and properties related to the tail fibers of bacteriophage T4

Abstract It is shown that adsorbability of T4 is regularly correlated with the extended state of the tail fibers, suggesting that in T4 fiber extension is a necessary condition for adsorption. Furthermore the extension and retraction of fibers is correlated with the dual sedimentation of T4 observed during ultracentrifugation. For T4, 38, which requires tryptophan for adsorption, electron microscopy shows the tail fibers to be extended in the presence of tryptophan and retracted in its absence. Phages with retracted fibers (no tryptophan) show a faster sedimentation than those with extended fibers (with tryptophan). In the absence of tryptophan T4, 38 does not show fiber extension even at pH 7, a condition sufficient for nontryptophan-requiring T4, whose fibers are retracted at pH 5. A conditional lethal mutation in gene 37 of phage T4D results in phages which lack tail fibers entirely. These phages no longer adsorb. In the ultracentrifuge, only the fast form can be observed whether at pH 7 or 5. Phages with extended fibers are more rapidly inactivated by ultrasonic waves than phages with retracted fibers. Measurements on electron micrographs show that the head size of T4 is invariant. A model of the functioning fiber apparatus is proposed and discussed.

Structure of the Tobacco Mosaic Virus Particle; Polymerization of Tobacco

Publisher Summary The chapter describes a critical analysis of the molecular weight of tobacco mosaic virus (TMV) and with polymerization of TMV protein. TMV has a very high molecular weight and measurements of double refraction of flow led to the conclusion that the particles are rod-shaped. The molecular weight of TMV has been determined adequately by physicochemical methods and measurements with the electron microscope. These yielded with fair uniformity a value close to 40 million. A value of about 23 A for the pitch of the helix of the virus was determined from X-ray diffraction measurements, and pertains to the virus in wet gels. In the determination of molecular weight with the electron microscope, it is desirable to utilize a technique that does not depend upon the retention of the wet particle dimensions. Some of the earliest determinations of molecular weight were done by sedimentation and diffusion. Molecular weights obtained by this method do not depend on assumptions about the molecular configuration. Light scattering has been used extensively for the determination of particle weight. The method is particularly useful because of its sensitivity over a wide range of particle sizes and its ability to provide information on particle shape. Subsequent studies have established the correctness of the assumption that water is released upon polymerization. TMV, a protein seems to be a trimer of the chemical subunit. Its polymerization has been studied primarily by light scattering and osmotic pressure methods. Within certain limits, the polymerization can be interpreted quite accurately in terms of the mathematics of condensation polymerization. Accompanying the release of water molecules upon polymerization is an increase in partial specific volume. Hydrogen ions are bound during polymerization.

Serum Lipid Levels in Normal Persons Findings of a Cooperative Study of Lipoproteins and Atherosclerosis

Measurements of Sf 12-20, Sf 20-100, and total serum cholesterol made on 10,690 men and 3,404 women are reported and the relation of lipid level to race, source, age, sex, blood pressure, and weight is described. Distributions for men 40 to 59 are reported in detail. The groups studied, while not selected as representative of the population at large, were remarkably similar in their lipid levels. The lipid levels of only 2 of the 33 groups—Los Angeles and the prisoners—differed significantly from the average. No convincing explanation for either of these exceptions was discovered. The data in this study were mainly from a white population. Data for nonwhites came primarily from 2 aberrant groups and were too meager to allow a clear characterization of lipid levels. The levels for nonwhites from these 2 sources were closer to those of the white members of these groups than to the levels of the general population. Cholesterol levels for men and women were found to be about the same at age 20. For both sexes the level rises with age but at first the rise is much greater for men than women. Above age 50, however, the level is higher for women than men and the level for women continues to rise after that age—at least within the age series for this study. The level for men reaches a peak at age 55, after which it declines. The relation of age and sex with lipid level for Sf 12-20 and Sf 20-100 appeared to be similar to that for cholesterol. Correlations of lipid levels with blood pressure and weight were positive but very low. Hypertension or obesity, however, is associated with some elevation of lipid levels. Sf 20-100 was found to be the most sensitive of the 3 lipid measures to sex and race differences. In the age group 40 to 59 it was the only one that exhibited a definite race and sex differential. In addition, it had the highest correlation with weight and with blood pressure.

Electrophoresis and phage susceptibility studies on a filament-producing variant of the E. coli B bacterium.

Abstract A variant of E. coli B bacterium, which we have called the F variant, has been found to exist in two distinct forms, fast and slow, which differ by a factor of almost two in electrophoretic mobility. The lower mobility of the slow form has been shown to be due to the presence of filaments, visible in electron micrographs, which exert a viscous drag. The filaments can be stripped off by mechanical agitation. De-filamented slow bacteria have the same mobility as non-filamented fast bacteria, indicating that the surface charge density is the same for the two forms. The bacteria are not killed by the stripping process and their progeny are filamented. The F variant appears to be similar to a phage semi-resistant variant, reported by Wahl 10 , which can exist in two states, refractory and receptive. The filamented bacteria are less susceptible to infection by a number of the T phages than de-filamented bacteria, and a preparation of filaments inactivated these phages. Bacteria selected for resistance to T 1 were found to be non-filamented and remained so on subculturing. The transition between the filamented and the non-filamented forms is rapid as is the transition between the refractory and receptive states. The probability of the transition is of the order of IO −3 per bacterium per division and is the same in both directions. It was noted that the filamented bacteria have a greater tendency to agglutinate spontaneously than the non-filamented. The same difference exists between smooth and rough forms. However, no detailed study was made of the colony morphology of the filamented variants.

The hydration of viruses.

Publisher Summary The size and shape of virus nucleoprotein particles can be evaluated unambiguously only when the degree of hydration is known. This chapter discusses several methods that are available for the determination of the hydration of protein crystals. These include the gravimetric analysis of crystals before and after drying, density determinations of crystals, analyses of secondary solute concentrations in equilibrium with crystals, X-ray diffraction analyses of crystal lattice dimensions in the hydrated and in the unhydrated state, and optical analyses of crystals. Only the X-ray diffraction and the optical methods actually have been applied to the crystals of virus nucleoproteins. Most methods of investigating hydration, particularly hydration of particles in solution, fall into three categories. The first category provides information about the total displacement of the hydrated particle. This category includes the direct displacement method of Lauffer and Taylor and methods involving various combinations of sedimentation, diffusion, rotational diffusion, and viscosity. The second category evaluates the effective specific volume of the hydrated particle such as sedimentation in media of different densities. The third category evaluates directly the volume or the mass of solvate bound by the particle. This category includes the methods that presumably determine the amount of solvent not free to dissolve a secondary solute such as vapor pressure determinations, freezing point depressions, boiling point elevations, and the distribution of secondary solute among phases or across membranes. Direct gravimetric or chemical analyses and X-ray diffraction analyses of crystals also fall within this classification.

Electrophoresis by the microscope method: a simple experimental assembly.

Abstract 1. 1. A new assembly for microelectrophoresis is described. It consists of an electrode unit properly separated from the test suspension for the avoidance of contamination, and a Northrop-Kunitz cell arranged laterally, that is, with its long and short axes horizontal and its intermediate axis vertical. 2. 2. The performance of the new assembly has been compared with those of the conventional Abramson-Moyer horizontal and vertical cells by mobility studies on erythrocytes of man, guinea pig, and rabbit, and has been found equally reliable. 3. 3. It was concluded that the new arrangement is capable of performing satisfactorily all of the functions for which both the conventional horizontal and the conventional vertical arrangements have been used previously.

Polymerization-Depolymerization of Tobacco Mosaic Virus Protein: I. Kinetics

It was shown that a reversible endothermic association of TMV protein subunits (A protein) can take place at pH values below the isoelectric point as well as at pH 6.5. The polymerization occurring below the isoelectric point was found to be more complex than that at pH 6.5 probably because products other than the usual TMV-like rods were formed in addition to those rods and also because side-to-side aggregation of the rods took place readily. Kinetic studies indicated that polymerization can be treated as a second-order linear condensation. The rate of polymerization was found to be a critical function of pH, having a maximum value near pH 4.3. This behavior is at variance with the hypothesis that hydrogen-bonded carboxyl pairs play a dominant rate-determining role in the association of subunits. The dependence of the rate on pH was interpreted to indicate that electrostatic forces between subunits are a significant controlling factor in the polymerization of TMV protein.It was shown that a reversible endothermic association of TMV protein subunits (A protein) can take place at pH values below the isoelectric point as well as at pH 6.5. The polymerization occurring below the isoelectric point was found to be more complex than that at pH 6.5 probably because products other than the usual TMV-like rods were formed in addition to those rods and also because side-to-side aggregation of the rods took place readily. Kinetic studies indicated that polymerization can be treated as a second-order linear condensation. The rate of polymerization was found to be a critical function of pH, having a maximum value near pH 4.3. This behavior is at variance with the hypothesis that hydrogen-bonded carboxyl pairs play a dominant rate-determining role in the association of subunits. The dependence of the rate on pH was interpreted to indicate that electrostatic forces between subunits are a significant controlling factor in the polymerization of TMV protein.Abstract It was shown that a reversible endothermic association of TMV protein subunits (A protein) can take place at pH values below the isoelectric point as well as at pH 6.5. The polymerization occurring below the isoelectric point was found to be more complex than that at pH 6.5 probably because products other than the usual TMV-like rods were formed in addition to those rods and also because side-to-side aggregation of the rods took place readily. Kinetic studies indicated that polymerization can be treated as a second-order linear condensation. The rate of polymerization was found to be a critical function of pH, having a maximum value near pH 4.3. This behavior is at variance with the hypothesis that hydrogen-bonded carboxyl pairs play a dominant rate-determining role in the association of subunits. The dependence of the rate on pH was interpreted to indicate that electrostatic forces between subunits are a significant controlling factor in the polymerization of TMV protein.

The size of T3 DNA

The nucleic acid of the bacteriophage T3 has been studied with the electron microscope in order to determine whether it exists either as a single unit or as several pieces of equal or varying size. The nucleic acid strands, obtained by mild alkali treatment of the virus, were oriented on collodion films and shadowed perpendicular to their length. None of the strands exhibited any branching, being continuous from one end to the other, and their diameters were found to be relatively constant. Measurement of seven such strands revealed a mean length of 14·0 ± 0·6 μ . The relatively good agreement of this value with that arrived at from theoretical calculations can be interpreted to mean that all of the T3 DNA is in one piece.

Dual sedimentation of T2 bacteriophage of Escherichia coli

Abstract For T2 bacteriophage, diffusion coefficients of 3.25·10 −8 cm 2 /sec and 2.63·10 −8 cm 2 /sec were obtained in pH 5 and pH 7 buffers, respectively. The transition limits for dual sedimentation encompass approximately one-half pH units, with a central value at about pH 6.1. Sedimenting the virus from a medium of one pH directly into a second medium of greater density and different pH has indicated that the sedimentation rate change is quite sharp and complete within a few minutes after passing through the interface. s 5 / D 5 differs significantly from s 7 / D 7 but not enough to represent one-to-one aggregation. It is, therefore, assumed that the molecular weight is the same at pH 7 and pH 5. It follows from this assumption and the experimental results that f s 7 / f s 5 is significantly greater than f D 7 / f D 5 . A model has been found which can account for all of these facts. It is assumed that at pH 5 the particle is tadpole-shaped but that at pH 7 it projects thin filaments laterally from the tail. Such filaments have been demonstrated with the electron microscope. Calculations of friction coefficients made for complex ellipsoidal models approximating the actual models discussed above yield results consistent with the experimental observations, if it is assumed that the particles are oriented randomly during diffusion but sediment in the direction of their longest axis.