Polypeptide solutions

Dissolve the protein or peptide to be conjugated at a concentration of lOmg/ml in 0.5M sodium carbonate, pH 9.5. Mix the activated liposome suspension with the polypeptide solution at the desired molar ratio to effect the conjugation. Mixing the equivalent of 4 mg of protein per mg of total lipid usually results in acceptable conjugates. 

Since Robinson [1] discovered cholesteric liquid-crystal phases in concentrated a-helical polypeptide solutions, lyotropic liquid crystallinity has been reported for such polymers as aromatic polyamides, heterocyclic polymers, DNA, cellulose and its derivatives, and some helical polysaccharides. These polymers have a structural feature in common, which is elongated (or asymmetric) shape or chain stiffness characterized by a relatively large persistence length. The minimum persistence length required for lyotropic liquid crystallinity is several nanometers1. 

Now we consider an experiment in which a static electric field is suddenly applied to a dilute polypeptide solution. If the rates of interconversions between helix and random-coil units are much faster than those of rotational motions of the entire dissolved polymer molecule as well as of local segments of it, there will be an increase in the dielectric constant which approaches a constant value (ds)ch with time t. This relaxation process is a kind of chemical relaxation, because the helix-coil interconversions responsible for it may be regarded as chemical reactions. Its detailed study should provide information about such elementary processes as those illustrated in Eqs. (E-13) and (E-15). This is Schwarz s basic idea. 

C. Robinson. Trans. Faraday Soc. 52, 571-92 (1956). Birefringence of liquid-crystalline polypeptide solutions. 

Formation of Liquid Crystals in Polypeptide Solutions 1.1 Introduction... 

Fig. 1. Temperature-composition phase diagram of polypeptide solutions...

The phase diagram of the polypeptide solutions is shown schematically in Fig. 1. According to the Flory theory, the relation between the concentration at the A point (Vja) and the axial ratio (r) is represented as follows ... 

However, only limited experimental studies on the thermodynamic properties of polypeptide solutions have been carried out. The results of vapor sorption studies for PBLG and poly(P-benzyl L-aspartate) solutions at high polymer concentrations by Flory and Leonard could not be explained by the Flory model, but could be explained by assuming that mixing of solvent with flexible side chains dominates the thermodynamic behavior at high concentrations. Rai and Miller obtained similar results for the PBLG-dimethylformamide (DMF) system at high concentrations. They also showed that the results could be explained by the Wee-MiUer theory in which modification of Flory s lattice theory to allow for side chain... 

Miller et al. have initiated studies to elucidate the kinetics of forming the ordered phase in the polypeptide solutions. When the isotropic solution is temperature-jumped across the biphasic region into the region in which the ordered phase is stable, the kinetics can be described by a nucleation and growth mechanism with many similarities to the kinetics of polymer crystallization. They have also shown that the kinetic process can be divided into two time scales the conversion of the randomly oriented rods to a random array of locally oriented rod domains, followed by growth of some domains at the expense of others. 

Kimura, H. Hosino, M. Nakano, H. Statistical theory of cholesteric ordering in hard-rod fluids and liquid crystalline properties of polypeptide solutions. J. Phys. Soc. Jpn. 1982, 51 (5), 1584-1590. 

Other Variables. The effect of the polypeptide molecular weight upon a has not yet been conclusively established for any polypeptide-organic solvent system. Recent extensive studies of the charge-induced transition of polyglutamic acid in aqueous solution have shown an increase in a with a reduction in molecular weight 15). Similarly the influence of polypeptide solute concentration is not yet clear, though Ackermann and Riiterjans 1) have demonstrated a remarkably large effect of this variable upon AH0 in PBG. Neither of these points is discussed further in the present paper. 

All of the above experiments were performed on dilute solutions of the polymers in order to reduce molecular interactions to a minimum. We have recently become interested in concentrated polypeptide solutions and their behavior when subjected to an ordering field. Solutions of PBLG in benzene and dioxane were originally reported to be extremely viscous (4) and presumably highly aggregated in an end-to-end manner. 

How many ATP equivalents are consiuned with the incorporation of an amino acid into a polypeptide SOLUTION... 

LCs were the earliest studied structures, in which polypeptide homopolymer rods pack in an ordered manner to form smectic, nematic, and cholesteric phases. The smectic LCs are mainly formed by polypeptide homopolymers with identical polymer length. The cholesteric phase can be prepared by synthetic polypeptides with polydisperse chain length. The nematic phase can be regarded as a special example of the cholesteric phase with an infinite cholesteric pitch. The cholesteric pitch and chirahty in the polypeptide LCs are dependent on many factors, such as temperature, polymer concentration, solvent nature, and polypeptide cOTiformation. Deep understanding of such phenomena is necessary for preparation of ordered polypeptide assembles with delicate stmctures. The addition of denaturing solvent to polypeptide solution can lead to an anisotropic-isotropic reentrant transition at low temperatures where the intramolecular helix-coil transformation occurs. However, the helical structure is more stable in LC phase than in dilute solution due to the conformational ordering effect. 

Robinson C (1961) Liquid-crystalline structures in polypeptide solutions. Tetrahedron 13 219-234... 

Robinson C, Ward JC, Beevers RB (1958) Liquid crystalline structure in polypeptide solutions. Part 2. Discuss Earaday Soc 25 29-42... 

Although instances of lyotropic PLCs predate studies of thermotropic PLCs, as they involved solutions of comparatively esoteric species — virus particles and helical polypeptides — studies of these liquid crystals were isolated to a few laboratories. Nevertheless, observations on these lyotropic PLCs did stimulate the first convincing theoretical rationalizations of spontaneously ordered fluid phases (see below). Much of the early experimental work was devoted to characterizing the texture of polypeptide solutions. (23) The chiral polypeptides (helical rods) generate a cholesteric structure in the solution the cholesteric pitch is strongly dependent on polymer concentration, dielectric properties of the solvent, and polymer molecular weight. Variable pitch (<1 - 100 pm) may be stabilized and locked into the solid state by (for example) evaporating the solvent in the presence of a nonvolatile plasticizer.(24)... 

In the last section of the book, lyotropic systems are treated. These concern derivatives of cellulose in various solvents as well as solutions of synthetic PLCs in low molecular mass liquid crystal solvents and polypeptide solutions in water. The last article illustrates the tremendous variety of polymeric bio-mesogens encountered in living matter. 

We observe that the transition from the isotropic to liquid crystalline state at a critical concentration of the rod-like helical polypeptide solute is manifested dramatically in each of the six properties that were examined [16,17] (Table 11.1). 

Priftis, D., Tirrell, M., 2012. Phase behaviour and complex coacervalion of aqueous polypeptide solutions. Soft Matter 8, 9396—9405. 

On the contrary, it is observed that with some proteins, the viscosity actually decreases when they are treated with 6 M guanidinium chloride. In such cases, one assumption is that the protein may be fibrous in nature and that denaturation has given it more flexibility as a random eoil. An example of such a case is afforded by poly(Y-benzyl-L-glutamate). The viscosity of this polypeptide solution actually decreases upon denaturation meaning that this polypepUde exists as a rigid rod in its native eondition and the random coil conformation upon denaturation is the more flexible form. The same is true about the protein collagen also. 

Cameretti, L.R and Sadowski, G., 2008. Modeling of aqueous amino acid and polypeptide solutions with PC-SAFT. Chem. Eng. Proc., 47 1018. 

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