An efficient freeze-drying apparatus

Summary A freeze-drying apparatus with a practical temperature regulating system is described. Degassing, drying and embedding all take place in the drying chamber. The drying temperature can be set at a number of fixed temperature levels which may be chosen anywhere between -70° C and +60° C.     

A simple method for freeze-drying of macromolecules and macromolecular complexes

We present a simple approach for effective freeze-drying and rotary shadowing of large molecules, molecular assemblies, and cell organelles. Simply, a suspension of specimen is adsorped to a glass coverslip, stabilized, and rinsed with 30% methanol. A second coverslip is "sandwiched" on top, and excess methanol is withdrawn from the edges then frozen by plunging into liquid nitrogen and split. Following either rotary or unidirectional shadowing and replication, the coverslip is dissolved in hydrofluoric acid. In addition to avoiding the problems encountered with air-drying specimens for rotary shadowing, the technique also reproducibly provides the thin layer of solution necessary for proper freeze-drying, regardless of how hydrophobic the sample is. The "glass sandwich" technique allows modification of the glass substrate (making it hydrophobic with carbon or hydrophilic by soaking it in alcian blue) which clearly alters the shape of macromolecular assemblies such as myosin filaments and decorated thin filaments.     

A simple automatic dispensing apparatus

A simple dispenser using a 2-ml disposable syringe is described. The range of operation is 0.02–1.5 ml and an unusual accuracy is obtained by employing a new principle for dispensers: the dispensed volume is only a fraction of total tidal flow of fluid in the dispenser.     

A simple apparatus for measuring cell settling velocity

Accurate cell settling velocity determination is critical for perfusion culture using a gravity settler for cell retention. We have developed a simple apparatus (a "settling column") for measuring settling velocity and have validated the procedure with 15-μm polystyrene particles with known physical properties. The measured settling velocity of the polystyrene particles is within 4% of the value obtained using the traditional Stokes' law approach. The settling velocities of three hybridoma cell lines were measured, resulting in up to twofold variation among cell lines, and the values decreased as the cell culture aged. The settling velocities of the nonviable cells were 33-50% less than the corresponding viable cells. The significant variation of settling velocities among cell populations and growth phases confirms the necessity of routine measurement of this property during long-term perfusion culture.     

A simple pressure filtration apparatus for field use

A simple apparatus for pressure-filtering water samples in the field is described. It is used in conjunction with the low pressure outlet of a standard regulator attached to an aqualung. The apparatus is useful in situations where electricity to run electric vacuum pumps is not available and is superior to conventional hand vacuum pumps.     

A simple, continuous-flow ultrafiltration apparatus

A continuous-flow, inverted ultrafiltration apparatus has been made, which permits protein solutions to be concentrated rapidly and has allowed the fractionation of some binary model mixtures. A major problem, which prevents such fractionations in conventional apparatus, has been identified. The design avoids shearing and overheating of labile solutions and appears to be suitable for both micro- and macro-scale applications.     

A simple,reliable rapid-mixing apparatus for continuous-flow studies

We have developed a simple and economical system for rapid mixing of solutions where a continuous-flow, chemically quenched mode of operation is appropriate. This has proved especially useful for studies of pyruvate dehydrogenase which produces a stable, enzyme-bound intermediate when the terminal acceptors are absent. It has also proved convenient for studies of the overall reaction in which fluorescence of pyridine nucleotide can be measured after quenching in alkaline solution.Syringes containing reactants are driven by a Harvard infusion pump, which provides sufficient speed and power (torque) to give good mixing with conventional commercially available mixing chambers and delay lines. Liquid chromatography fittings and valves are used for the switching operations necessary in the continuous-flow mode.