Effect on protein

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. 

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

Drought also has a profound effect on protein synthesis. In many plant tissues, a reduced water potential causes a reduction of total protein synthesis and a rapid dissociation of polyribosomes. The latter has been shown not to be the consequence of increase in ribonuclease activity (Hsiao, 1973 Dhindsa Bewley, 1976). For a specific protein, Jacobsen, Hanson Chandler (1986) have shown in barley leaves that water stress enhances the synthesis of one of the a-amylase isozymes. Using a cDNA probe they found that water-stressed leaves contained much more a-amylase mRNA than unstressed plants. 

Biochemical and genetic experiments in yeast have revealed that the b poly(A) tail and its binding protein, Pablp, are required for efficient initiation of protein synthesis. Further studies showed that the poly(A) tail stimulates recruitment of the 40S ribosomal subunit to the mRNA through a complex set of interactions. Pablp, bound to the poly(A) tail, interacts with eIF-4G, which in turn binds to eIF-4E that is bound to the cap structure. It is possible that a circular structure is formed and that this helps direct the 40S ribosomal subunit to the b end of the mRNA. This helps explain how the cap and poly(A) tail structures have a synergistic effect on protein synthesis. It appears that a similar mechanism is at work in mammalian cells. 

The nondihydropyridine calcium channel blockers have been shown to also decrease protein excretion in patients with diabetes,20 but the reduction in proteinuria appears to be related to the reductions in blood pressure. The maximal effect of nondihydropyridine calcium channel blockers on proteinuria is seen with a blood pressure reduction to less than 130/80 mm Hg and no additional benefit is seen with increased doses. Dihydropyridine calcium channel blockers, however, do not have the same effects on protein excretion, and may actually worsen protein excretion.17... 

T. W. Randolph, Phase separation of excipients during lyophilization Effects on protein stability, J. Pharm. Sci., 86(11), 1198 (1997). 

S. T. Tzannis and S. J. Prestrelski, Moisture effects on protein-excipient interactions in spray dried powders. Nature of destabilizing effects of sucrose, J. Pharm. Sci, 88(3), 360 (1999). 

Eggers, D.K. and Valentine, J.S. (2001) Crowding and hydration effects on protein conformation a study with sol-gel encapsulated proteins. Journal of Molecular Biology, 314, 911-922. 

This process of cross-linking does not appear have a major effect on protein secondary structure at room temperature. However, cross-links formed by reactions of formaldehyde with proteins retard, but do not eliminate, protein denaturation that occurs when proteins are heated to a temperature of approximately 70°C or above.7... 

It is obvious that the oxidation of protein molecules can have detrimental effects on protein structure and function. However, there are some unique methods in bioconjugation wherein controlled and purposeful oxidation is done to study protein-protein interactions (Chapter 28, Section 4). 

Note Some protocols avoid a reduction step, as it can lead to disulfide bond cleavage and detrimental effects on protein activity. As an alternative to reduction, add 50 pi of 0.2 M lysine in 0.5 M sodium carbonate, pH 9.5 to each ml of the conjugation reaction to block excess reactive sites. Block for 2 hours at room temperature. Other amine-containing small molecules may be substituted for lysine—such as glycine, Tris buffer, or ethanolamine. 

It is well known that solvents have a profound effect on protein conformation. It is often beneficial to apply the phenomena to the optimization of enzymatic reactions. For example, in the synthesis of the GABA... 

Oguchi). Thermal Effects on Protein, Nucleic Acid, and Viruses 5 189... 

Theory Cortisol (or hydrocortisone) was introduced in the year 1951, for the treatment of rheumatoid arthritis. It has a significant effect on protein metabolism. It also exerts widespread effects on carbohydrates, lipid and protein synthesis (or anabolism). The cardinal side effects such as excessive potassium excretion and sodium retention, enhanced gastric acidity, oedema, psychosis and negative nitogen balance are some of the exaggerated manifestations of the normal metabolite functions of cortisol. 

A protein, of course, is a polypeptide chain made up of amino acid residues linked together in a definite sequence. Amino acids are handed (except for glycine, in which the normally asymmetric o-carbon has two hydrogens), and naturally occurring proteins contain only L-amino acids. That handedness has far-reaching effects on protein structure, as we shall see, and it is very useful to be able to distin-... 

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