Ribonuclease heat denatured

The model polypeptide acetyltetraglycine ethyl ester (ATGEE) behaves in this manner. Citrates, sulfates, phosphates, acetates, and chlorides salt out ATGEE whereas phenol, perchlorates, tosylates, trichloroacetates, thiocyanates, iodides, and bromides salt in (8). The heat denaturation of ribonuclease also fits this cTass. 

The criterion however applies only to uncross-linked proteins, so that no conclusion can be drawn from the rather small increase, circa 20%, in the Stokes radius Rs upon heat denaturation measured by dynamic light scattering (DLS) for chymotrypsinogen, ribonuclease, and lysozyme [98], and for ribonuclease [99] for comparison, 5 M GuCl causes a 45% increase to / s of unreduced lysozyme [100],... 

Fig. 1 is a diagrammatic representation of a) the reductive denaturation of ribonuclease in 8 M urea with thioethanol (2-mercaptoethanol), b) its reoxidation in 8 M urea to one of the 105 possible disulfide bridge isomers, and c) its renaturation to the enzymically active form in urea-free medium, by disulfide exchange in the presence of traces of thioethanol. Formation of completely disordered structures results in irreversible denaturation, e. g. heat denaturation of ovalbu-... 

The reversible denaturation of polypeptides and proteins in dilute solutions can be studied by a variety of techniques, most commonly by observation of changes in optical rotatory properties (Yang and Doty, 1956, 1957). For example, Harrington and Schellman (1956) showed that bovine ribonuclease at pH 6.5 is reversibly heat denatured. This reversible transformation has been investigated at a variety of pH values (Hermans and Scheraga, 1961a, b) and the data are shown in Fig. 51. The transition tem-... 

Heat affects the conformation of proteins, and most proteins undergo fairly rapid heat denaturation somewhere between 333 and 363 A series of experiments was made by Roscoe and Fuller in which the surface adsorption behavior of bovine )8-lactoglobulin A, hen egg-white lysozyme and bovine pancreatic ribonuclease A was studied at a platinum electrode as a function of temperature using cyclic voltammetry. The protein solution and the electrochemical cell were separately immersed in the thermostated bath and allowed to equilibrate for 30 mins. The protein... 

Fig. 4. Temperature dependence of the specific enthalpy of denaturation of myoglobin and ribonuclease A (per mole of amino acid residues) in solutions with pH and buffer providing maximal stability of these proteins and compensation of heat effects of ionization (see Privalov and Khechinashvili, 1974). The broken extension of the solid lines represents a region that is less certain due to uncertainty in the A°CP function (see Fig. 2). The dot-and-dash lines represent the functions calculated with the assumption that the denaturation heat capacity increment is temperature independent.

In summary the deleterious effects of alkali on the proteins and the large-scale impracticality of the heat-shock (endogeneous ribonuclease) process, plus the accompanying proteolysis and denaturation of proteins, clearly indicate the need for better methods to facilitate the large-scale separation of nucleic acids from yeast proteins. 

Amino acid sequence - Secondary and tertiary structures can usually be destroyed (called denaturation) by heating a protein or changing the solvent environment (pH, salt content, organic content, etc.) in which the protein is dissolved. When the characteristic structure of a protein molecule in its physiological environment is lost, so too is the protein s normal function. If ribonuclease is heated to 80 C, it is converted from its normal, native state to a denatured state (Figure 6.20), which is unable to catalyze the cleavage of RNA. 

Analogous shifts in protein spectra have been observed as a result of conformational changes associated with denaturation. Initial reports on this phenomenon (see Ref 24) attributed the spectral difference to the transfer of the aromatie amino acids from the hydrophobic interior of the protein to the more aqueous surface environment as a result of the conformational change. Spectral changes for several proteins correlated well with independent measurements of denaturation such as intrinsic viscosity, circular dichroic spectra, and heat capacity measurements. For example, Edelhoch [26] compared the ribonuclease UV spectrum in buffer with that obtained in 6M guanidine hydrochloride (GuHCI). 

One of the most effective uses of optical rotation is in the study of kinetics and equilibria of protein denaturation. For example, Harrington and Schellman (1956) found that the values of [ ]d of ribonuclease become more negative if the protein is heated at pH 6.5 (see Fig. 101). This curve is... 

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