Buffer components, crystallization

Nucleation outcomes from solutions with initially the same composition may vary as a consequence of impurities, rates at which supersaturation was created, thermal histories, experimental techniques employed to detect precipitation, and solution volumes in which nucleation occurred. This is illustrated by comparing results of the selective crystallization of buffer components during freezing from various labora-tories.f The initial salt concentrations and the crystallization behavior of disodium phosphate during the freezing of sodium phosphate buffer solutions are shown in Table 1. Murase et report... 

Buffers are often added to control pH, but caution must be exercised when buffers are used in a formulation to be freeze dried. As discussed earlier, crystallization of either buffer component (acid or base) during freezing may cause a significant pH shift during freezing, thereby causing greater pH variation than would have been obtained in an unbuffered system. 

Crystal Structures.—Crystallization, a pre-requisite for diffraction studies, is a notoriously and unpredictably difficult exercise with new proteins. Carter and Carter have introduced a method which searches a large number of experimental variables (e.g., buffer components and pH) that can influence rates of crystallization. Random combinations of the variables are used to attempt crystallization and the resulting precipitated protein scored on an arbitrary crystallinity scale. After applying the appropriate statistic, a complete factorial experiment is set up using the conditions which promoted crystallization in the first experiment. 

The immediate question is How does one add a single component k from an external reservoir to the crystal according to Eqn. (2.4) without violating any structural constraints, that is, the fixed relations between the numbers of sublattice sites We denote a particular sublattice containing atoms (ions) of component k by x (x = 1,2,..., K) and write the exchange reaction between external reservoir (= buffer P) and crystal sublattice as... 

With electrochemical methods, we determine thermodynamic potentials of components in systems which contain a sufficiently large number of atomic particles. Since the systematic investigation of solid electrolytes in the early 1920 s, it is possible to change the mole number of a component in a crystal via the corresponding flux across an appropriate electrolyte (1 mA times 1 s corresponds to ca. 10 s mol). Simultaneously, the chemical potential of the component can be determined with the same set-tip under open circuit conditions. Provided both the response time and the buffer capacity of the galvanic cells are sufficiently small, we can then also register the time dependence of the component chemical potentials in the reacting solids. ... 

Lente insulin is a mixture of 30% semilente (an amorphous precipitate of insulin with zinc ions in acetate buffer that has a relatively rapid onset of action) with 70% ultralente insulin (a poorly soluble crystal of zinc insulin that has a delayed onset and prolonged duration of action). These two components provide a combination of relatively rapid absorption with sustained long action, making lente insulin a useful therapeutic agent. As with regular insulin, the time of onset, time to peak, and duration of action are dose-dependent. 

Once some crystals, even if only microcrystals, are observed and shown to be of protein origin (and one ardently hopes for this event) then optimization begins. Every component in the solution yielding crystals must be noted and considered (buffer, salt, ions, etc.), along... 

The Streptomyces PLD consists of two highly interacting components of similar topology [13]. Overall, the structure is very similar to die Nuc dimer. Each component consists of a /1-sheet of 8-9 strands surrounded by nine a-helices. The catalytic center is also very similar to that of the Nuc dimer. Crystallization with a phosphate buffer indicates that the phosphate head group of the substrate lies in contact with His, Lys and Asn residues contributed from both HKD domains [13]. 

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