Stability, protein

Under these conditions, it is possible to evaluate protein stability from denaturation experiments. This is not a subject of simply academic interest the increasing use of proteins in everyday use, for example as additives in washing powders, has made protein stability a matter of great practical importance, the more so since protein engineering has been used to improve stability properties. 

The equilibrium constant for the interaction between the two conformational forms is given by the expression  

The value of AG 0 can be determined from the observed values of AG in the region of the unfolding transition from the equation 

Experimentally, it is important that the urea and guanidinium chloride solutions used in stability studies are of the highest quality available. Urea solutions must be freshly prepared, since the compound undergoes decomposition in aqueous solution to form ammonium cyanate. Guanidinium chloride is a stronger denaturant than urea, but it cannot be used for studies of the dependence of stability on ionic strength. 

Unfolding can also be induced by temperature, and thermal denaturation curves (melting curves) are experimentally easier to obtain, since measurements are carried out only on a single protein solution. It is also easy to check the reversibility of the process by slowly cooling the denatured protein solution. The parameter A G°s can be obtained from melting curves provided either that the van t Hoff plot 

The other important elements in the engineering of a process to produce microspheres are the reproducibility, scalability, and aseptic operation of the process. The overall process must yield microspheres with the same characteristics from batch to batch. As there are a number of variables in the process (as listed in Table IV), the reproducibility of the overall process may be quite difficult to achieve. However, only a few variables are critical to the final microsphere characteristics, and, thus, if these variables are well regulated, the process should reproducibly manufacture the desired microspheres. One consideration often neglected by developers of novel methods for encapsulation is the scalability of the process. Many processes 

The development of a stable protein formulation for microencapsulation also includes consideration of the potential for protein-polymer interactions. For example, proteins that are very basic (high PI) may interact with the free acid groups generated by the degradation of polylactides. In this case, it may be necessary to add excipients such as polyionic compounds (anionic for protein binding, cationic for polymer binding) that prevent or reduce the interaction between the protein and the polymer. For polylactides, it may be unlikely that the protein will form a covalent adduct with 

CASE STUDIES OF DRUG DELIVERY FROM BIODEGRADABLE MICROSPHERES 

In the process of developing microsphere formulations for LHRH agonists, several different aspects of the formulation and the process were investigated. Ogawa and colleagues at Takeda Chemical Industries initially 

To verify that the in vitro and in vivo release rates were comparable, Ogawa and co-workers injected the microspheres into rats (Sprague-Daw-ley) and measured the amount of peptide remaining at the injection site over time (Ogawa et al, 1988c). The in vivo release was then compared to the release in vitro, which was performed by incubation of the microspheres in 33 mM phosphate buffer, pH 7.0, 0.05% Tween 80. As shown in Fig. 6, the in vivo and in vitro release were similar up to 21 days. However, the in vivo release decreased after 21 days, and 20% of the peptide remained after 35 days. Since significant bioerosion of the PLGA had occurred by 28 days, it 

Furthermore this means that the heat capacity difference between two states N and D, given by equation 6 

These parameters permit calculation of the standard Gibbs energy difference between the states of the protein. For a simple two-state transition of the type 

Using these relations the variation with temperature of the standard Gibbs energy change can be expressed in the following form 

This property is defined as the stability of the protein . The function described by eq. 13 is the so-called stability curve . By recalling the relation between the equilibrium constant K T) and the standard Gibbs 

Equation 13 is valid for the simple two-state 1 1 transition mechanism involving a constant A Cp value. For different transition stoichiometries or a temperature dependent A Cp value the stability equation will assume a more complex form (see below). 

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Water-soluble globular proteins usually have an interior composed almost entirely of non polar, hydrophobic amino acids such as phenylalanine, tryptophan, valine and leucine witl polar and charged amino acids such as lysine and arginine located on the surface of thi molecule. This packing of hydrophobic residues is a consequence of the hydrophobic effeci which is the most important factor that contributes to protein stability. The molecula basis for the hydrophobic effect continues to be the subject of some debate but is general considered to be entropic in origin. Moreover, it is the entropy change of the solvent that i... 

Inactivation and Removal of Viruses. In developing methods of plasma fractionation, the possibiHty of transmitting infection from human vimses present in the starting plasma pool has been recognized (4,5). Consequentiy, studies of product stabiHty encompass investigation of heat treatment of products in both solution (100) and dried (101) states to estabHsh vimcidal procedures that could be appHed to the final product. Salts of fatty acid anions, such as sodium caprylate [1984-06-17, and the acetyl derivative of the amino acid tryptophan, sodium acetyl-tryptophanate [87-32-17, are capable of stabilizing albumin solutions to 60°C for 10 hours (100) this procedure prevents the transmission of viral hepatitis (102,103). The degree of protein stabilization obtained (104) and the safety of the product in clinical practice have been confirmed (105,106). The procedure has also been shown to inactivate the human immunodeficiency vims (HIV) (107). 

Disulfides. The introduction of disulfide bonds can have various effects on protein stability. In T4 lyso2yme, for example, the incorporation of some disulfides increases thermal stability others reduce stability (47—49). Stabili2ation is thought to result from reduction of the conformational entropy of the unfolded state, whereas in most cases the cause of destabili2ation is the introduction of dihedral angle stress. In natural proteins, placement of a disulfide bond at most positions within the polypeptide chain would result in unacceptable constraint of the a-carbon chain. 

Cell Disruption Intracellular protein products are present as either soluble, folded proteins or inclusion bodies. Release of folded proteins must be carefully considered. Active proteins are subject to deactivation and denaturation, and thus require the use of gentle conditions. In addition, due consideration must be given to the suspending medium lysis buffers are often optimized to promote protein stability and protect the protein from proteolysis and deactivation. Inclusion bodies, in contrast, are protected by virtue of the protein agglomeration. More stressful conditions are typically employed for their release, which includes going to higher temperatures if necessaiy. For native proteins, gentler methods and temperature control are required. 

T Lazaridis, G Archontis, M Karplus. Enthalpic contribution to protein stability Atom-based calculations and statistical mechanics. Adv Protein Chem 47 231-306, 1995. 

Alber, T. Mutational effects on protein stability. Annu. Rev. Biochem. 58 765-798, 1989. 

Kellis, J.T., et al. Contribution of hydrophobic interactions to protein stability. Nature 333 784-786, 1988. 

Matsumura, M., Signor, G., Matthews, B.W. Substantial increase of protein stability by multiple disulfide bonds. Nature 342 291-293, 1989. 

With a knowledge of the methodology in hand, let s review the results of amino acid composition and sequence studies on proteins. Table 5.8 lists the relative frequencies of the amino acids in various proteins. It is very unusual for a globular protein to have an amino acid composition that deviates substantially from these values. Apparently, these abundances reflect a distribution of amino acid polarities that is optimal for protein stability in an aqueous milieu. Membrane proteins have relatively more hydrophobic and fewer ionic amino acids, a condition consistent with their location. Fibrous proteins may show compositions that are atypical with respect to these norms, indicating an underlying relationship between the composition and the structure of these proteins. 

Both attractive forces and repulsive forces are included in van der Waals interactions. The attractive forces are due primarily to instantaneous dipole-induced dipole interactions that arise because of fluctuations in the electron charge distributions of adjacent nonbonded atoms. Individual van der Waals interactions are weak ones (with stabilization energies of 4.0 to 1.2 kj/mol), but many such interactions occur in a typical protein, and, by sheer force of numbers, they can represent a significant contribution to the stability of a protein. Peter Privalov and George Makhatadze have shown that, for pancreatic ribonuclease A, hen egg white lysozyme, horse heart cytochrome c, and sperm whale myoglobin, van der Waals interactions between tightly packed groups in the interior of the protein are a major contribution to protein stability. 

GPCR function has been shown to be regulated by several different mechanisms. The number of receptors on the plasma membrane may be regulated by transcription, mRNA stability, biosynthetic processing, and protein stability. In addition, the function of receptors in the plasma membrane can be influenced by regulatory phosphorylation and by association with other proteins that determine the subcellular location of receptors relative to other signaling molecules. 

Linder ME, Deschenes RJ (2007) Palmitoylation policing protein stability and traffic. Nat Rev Mol Cell Biol 8 74—84... 

Strohmeier W (1968) Problem und Modell der homogenen Katalyse. 5 96-117 Sugiura Y, Nomoto K (1984) Phytosiderophores - Structures and Properties of Mugineic Acids and Their Metal Complexes. 58 107-135 Sun H, Cox MC, Li H, Sadler PJ (1997) Rationalisation of Binding to Transferrin Prediction of Metal-Protein Stability Constants. 88 71-102 Swann JC, see Bray RC (1972) II 107-144... 

The mechanism by which these solutes exert their influence on protein stability is uncertain. The phenomenon has been extensively studied by Timasheff and his colleagues and their conclusion is that all of the protein structure-stabilising compounds are preferentially excluded from contact with the surface of the protein (Timasheff, 1982). This explanation is rather different from that invoked in the water replacement hypothesis. 

VHL Regulator of protein stability Renal cell cancer... 

Because of the multiple degradation pathways that may take place at elevated temperature, protein stability monitoring data may not conform to the Arrhenius relationship, and the maximum temperature selected for accelerated stability studies must be carefully selected. Gu et al. [32] described the different mechanisms of inactivation of interleukin-1 (3 (IL-1 (3) in solution above and below 39°C. In this example, the multiple mechanisms precluded the prediction of formulation shelf life from accelerated temperature data. In contrast, by working at 40° C and lower, Perlman and Nguyen [33] were able to successfully extrapolate data from stability studies of tissue plasminogen activator down to 5°C. 

Properly folded native proteins tend to aggregate less than when unfolded. Solution additives that are known to stabilize the native proteins in solution may inhibit aggregation and enhance solubility. A diverse range of chemical additives are known to stabilize proteins in solution. These include salts, polyols, amino acids, and various polymers. Timasheff and colleagues have provided an extensive examination of the effects of solvent additives on protein stability [105]. The unifying mechanism for protein stabilization by these cosolvents is related to their preferential exclusion from the protein surface. With the cosolvent preferentially excluded, the protein surface is... 

Globular proteins are known to act as polymeric stabilizers of protein structure in solution. Wang and Hanson [106] review the mechanisms of protein stabilization by serum albumin, and it has been included in... 

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