Ultracentrifuge - AbsoluteAstronomy.com

The ultracentrifuge is a centrifuge

Centrifuge

A centrifuge is a piece of equipment, generally driven by an electric motor , that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis...

optimized for spinning a rotor at very high speeds, capable of generating acceleration as high as 2,000,000 g (approx. 19,600 km/s²). There are two kinds of ultracentrifuges, the preparative and the analytical ultracentrifuge. Both classes of instruments find important uses in molecular biology, biochemistry and polymer science.

History

Theodor Svedberg

Theodor H. E. Svedberg was a Swedish chemist and Nobel laureate, active at Uppsala University. His work with colloids supported the theories of Brownian motion put forward by Einstein and the Polish geophysicist Marian Smoluchowski...

invented the analytical ultracentrifuge in 1925, and won the Nobel Prize in Chemistry

Nobel Prize in Chemistry

The Nobel Prize in Chemistry is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of chemistry. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895, awarded for outstanding contributions in chemistry, physics, literature,...

in 1926 for his research on colloids and proteins using the ultracentrifuge.

The vacuum ultracentrifuge was invented by Edward Greydon Pickels. It was his contribution of the vacuum

Vacuum

In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...

which allowed a reduction in friction

Friction

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...

generated at high speeds. Vacuum systems also enabled the maintenance of constant temperature

Temperature

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

.

In 1946, Pickels cofounded Spinco (Specialized Instruments Corp.) and marketed an ultracentrifuge based on his design. Pickels, however, considered his design to be complicated and developed a more “foolproof” version. But even with the enhanced design, sales of the technology remained low, and Spinco almost went bankrupt. The company survived and was the first to commercially manufacture ultracentrifuges, in 1947. In 1949, Spinco introduced the Model L, the first preparative ultracentrifuge to reach a maximum speed of 40,000 rpm. In 1954, Beckman Instruments (now Beckman Coulter

Beckman Coulter

Beckman Coulter Inc., is a company that makes biomedical laboratory instruments. Founded by Caltech professor Arnold O. Beckman in 1935 as National Technical Laboratories to commercialize a pH meter that he had invented, the company eventually grew to employ over 10,000 people, with $2.4 billion in...

) purchased the company, forming the basis of its Spinco centrifuge division.

Analytical ultracentrifuge

In an analytical ultracentrifuge, a sample being spun can be monitored in real time through an optical detection system, using ultraviolet light absorption and/or interference optical refractive index sensitive system. This allows the operator to observe the evolution of the sample concentration versus the axis of rotation profile as a result of the applied centrifugal field. With modern instrumentation, these observations are electronically digitized and stored for further mathematical analysis. Two kinds of experiments are commonly performed on these instruments: sedimentation velocity experiments and sedimentation equilibrium experiments.

Sedimentation velocity experiments aim to interpret the entire time-course of sedimentation, and report on the shape and molar mass of the dissolved macromolecules, as well as their size-distribution. The size resolution of this method scales approximately with the square of the particle radii, and by adjusting the rotor speed of the experiment size-ranges from 100 Da

Atomic mass unit

The unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of...

to 10 GDa can be covered. Sedimentation velocity experiments can also be used to study reversible chemical equilibria between macromolecular species, by either monitoring the number and molar mass of macromolecular complexes, by gaining information about the complex composition from multi-signal analysis exploiting differences in each components spectroscopic signal, or by following the composition dependence of the sedimentation rates of the macromolecular system, as described in Gilbert-Jenkins theory.

Sedimentation equilibrium experiments are not concerned only with the final steady-state of the experiment, where sedimentation is balanced by diffusion opposing the concentration gradients, resulting in a time-independent concentration profile. Sedimentation equilibrium distributions in the centrifugal field are characterized by Boltzmann distributions. This experiment is insensitive to the shape of the macromolecule, and directly reports on the molar mass of the macromolecules and, for chemically reacting mixtures, on chemical equilibrium

Chemical equilibrium

In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...

constants.

The kinds of information that can be obtained from an analytical ultracentrifuge include the gross shape of macromolecule

Macromolecule

A macromolecule is a very large molecule commonly created by some form of polymerization. In biochemistry, the term is applied to the four conventional biopolymers , as well as non-polymeric molecules with large molecular mass such as macrocycles...

s, the conformational changes in macromolecules, and size distributions of macromolecular samples. For macromolecules, such as protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s, that exist in chemical equilibrium

Chemical equilibrium

with different non-covalent complexes, the number and subunit stoichiometry

Stoichiometry

Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers...

of the complexes and equilibrium constant

Chemical equilibrium

constants can be studied.

Analytical ultracentrifugation has recently seen a surprising rise in use due to the development of an NIH supported software package, SedFit.

Visit The AUC Wiki and The NIH SedFit page for more information.

Preparative ultracentrifuge

Preparative ultracentrifuges are available with a wide variety of rotors suitable for a great range of experiments. Most rotors are designed to hold tubes that contain the samples. Swinging bucket rotors allow the tubes to hang on hinges so the tubes reorient to the horizontal as the rotor initially accelerates. Fixed angle rotors are made of a single block of metal and hold the tubes in cavities bored at a predetermined angle. Zonal rotors are designed to contain a large volume of sample in a single central cavity rather than in tubes. Some zonal rotors are capable of dynamic loading and unloading of samples while the rotor is spinning at high speed.

Preparative rotors are used in biology for pelleting of fine particulate fractions, such as cellular organelles (mitochondria, microsome

Microsome

In cell biology, microsomes are vesicle-like artifacts re-formed from pieces of the endoplasmic reticulum when eukaryotic cells are broken-up in the laboratory; by definition, microsomes are not ordinarily present in living cells....

s, ribosomes) and virus

Virus

A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

es. They can also be used for gradient

Gradient

In vector calculus, the gradient of a scalar field is a vector field that points in the direction of the greatest rate of increase of the scalar field, and whose magnitude is the greatest rate of change....

separations, in which the tubes are filled from top to bottom with an increasing concentration of a dense substance in solution. Sucrose

Sucrose

Sucrose is the organic compound commonly known as table sugar and sometimes called saccharose. A white, odorless, crystalline powder with a sweet taste, it is best known for its role in human nutrition. The molecule is a disaccharide composed of glucose and fructose with the molecular formula...

gradients are typically used for separation of cellular organelles. Gradients of caesium

Caesium

Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C , which makes it one of only five elemental metals that are liquid at room temperature...

salts are used for separation of nucleic acids. After the sample has spun at high speed for sufficient time to produce the separation, the rotor is allowed to come to a smooth stop and the gradient is gently pumped out of each tube to isolate the separated components.

Visit http://www.thermo.com/eThermo/CMA/PDFs/Various/File_6810.pdf

Hazards

The tremendous rotational kinetic energy

Kinetic energy

The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...

of the rotor in an operating ultracentrifuge makes the catastrophic failure

Catastrophic failure

A catastrophic failure is a sudden and total failure of some system from which recovery is impossible. Catastrophic failures often lead to cascading systems failure....

of a spinning rotor a serious concern. The stresses of routine use and harsh chemical solutions eventually cause rotors to deteriorate. Proper use of the instrument and rotors within recommended limits and careful maintenance of rotors to prevent corrosion and to detect deterioration is necessary to avoid this hazard.

External links

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

History

Analytical ultracentrifuge

Preparative ultracentrifuge

Hazards

See also

External links