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M A Lauffer

Publications and source records attributed to M A Lauffer.

At least 19 recordsLinked to original sources
PubMed1985

Effect of dipolar ions on the entropy-driven polymerization of tobacco mosaic virus protein.

The effect of the dipolar ions, glycine, glycylglycine, and glycylglycylglycine on the polymerization of tobacco mosaic virus (TMV) protein has been studied by the methods of light scattering and ultracentrifugation. All three dipolar ions promote polymerization. The major reaction in the early stage is transition from the 4 S to the 20 S state. As in the absence of dipolar ions, the polymerization is enhanced by an increase in temperature; it is endothermic and therefore entropy-driven. The effect of the dipolar ions can be understood in terms of their action as salting-out agents; they increase the activity coefficient of TMV A protein, the 4 S material, and thus shift the equilibrium toward the 20 S state. The salting-out constants, K, for the reaction in 0.10 ionic strength phosphate buffer at pH 6.7 was found by the light scattering method to be 1.6 for glycine, 2.5 for glycylglycine, and 2.5 for glycylglycylglycine. A value of 2.7 was obtained by the ultracentrifugation method for glycylglycine in phosphate buffer at 0.1 ionic strength and pH 6.8 at 10 degrees C. For both glycine and glycylglycine, K increases when the ionic strength of the phosphate buffer is decreased. This result suggests that electrolytes decrease the activity coefficient of the dipolar ions, a salting-in phenomenon. However, the salting-in constants evaluated from these results are substantially higher than those previously determined by solubility measurements. The effect of glycine and glycylglycine on polymerization was studied at pH values between 6.2 and 6.8. The effectiveness of both dipolar ions is approximately 50% greater at pH 6.8 than at pH 6.2. The variation of the extent of polymerization with pH in the presence of the dipolar ions is consistent with the interpretation that approximately one hydrogen ion is bound for half of the polypeptide units in the polymerized A protein.

Capsid Proteins↗
PubMed1985

Entropy-driven polymerization of ribgrass virus protein.

Holmes ribgrass virus (HRV), because of serological results, is regarded as a distantly related strain of tobacco mosaic virus (TMV). HRV protein differs substantially in amino acid sequence from TMV protein, especially in that it contains one histidine residue and three methionine residues, compared to none of either for TMV protein. Ultracentrifugation and hydrogen ion titration data on HRV protein, similar to those obtained previously for the early stage polymerization of TMV and E66 proteins, demonstrated some similarities and more distinct differences from those of the other two proteins. The major similarities are that the early polymerization of HRV protein is entropy driven and the first major polymerized product is a 20 S component, presumably a double disk or two-turn helix, as in the case of the other proteins. The major differences are that the unpolymerized HRV protein sediments at 3 S rather than at the 4 S for the others; it is presumably a dimer of the polypeptide chain. The enthalpy of polymerization per mole of A protein, delta H*, is 18,400 cal for HRV protein, compared to about 30,000 for TMV protein. One mol of H+ ion/mol HRV A protein, compared to 1.5 for TMV and E66 proteins, is bound during polymerization to the 20 S state. Contrasted with the other proteins, very little if any electrical work contribution was detected for the HRV protein. A major difference was found in hydrogen ion titration. Unpolymerized HRV protein binds hydrogen ions significantly in the unpolymerized A protein state, unlike the A proteins from the other two viruses.

Hydrogen Bonding↗
PubMed1985

Comparison of the entropy-driven polymerization reactions of E66 and vulgare tobacco mosaic virus proteins.

The effects of temperature (T), ionic strength (mu), and pH on the polymerization of the coat protein of the E66 strain of tobacco mosaic virus (TMV) from the 4 S form (A), a trimer of the polypeptide chain, to the 20 S form (D) were investigated by the method of sedimentation velocity. Interpretations of thermodynamic parameters were based on only those data obtained in experiments for which reversibility could be demonstrated both by lowering temperature and by lowering concentration. E66 protein differed from vulgare TMV in that, in position 140, lysine replaced asparagine. Thus, E66 protein should be less hydrophobic than vulgare protein and K's, the salting-out constant, should be less. The charge on unpolymerized E66 protein was -3 proton units per polypeptide chain, compared to -4 for vulgare protein. The electrical work contribution, delta W*el, for E66 protein should be (-3/-4)2, or 0.5625 that for vulgare. The results were that delta W*el at pH 6.7, 15 degrees C, and mu = 0.1 was 0.700 kcal/mol for E66 protein compared to 1.22 for vulgare. The experimental ratio was 0.574; K's = 2.16 for E66 compared to 4.93 for vulgare. Hydrogen ions (1.5) were bound per A unit, or 0.5 per polypeptide chain, in the formation of D from A. delta H*, the enthalpy change per mole of A, was 33 kcal at pH 6.7 and 36 at pH 6.9, compared to 30 at both pH values for vulgare protein. delta S*, the entropy change per mole of A, was +132.1 e.u. for E66 compared to 127.4 for vulgare. Entropy-driven processes are found in dynamic biological situations. Ready reversibility at biological temperatures is a requirement, yet the polymer structures must be strong and well ordered. This is achieved through a large number of weak bonds between subunits, combined with ready reversibility under slightly changed conditions. The significant role of water is to facilitate depolymerization by binding to subunits.

Biopolymers↗
PubMed1983

Calcium ion binding by tobacco mosaic virus.

Calcium ion titrations were performed on solutions of tobacco mosaic virus using a calcium-specific ion-exchange electrode. Scatchard analyses were used to obtain the number of calcium ion binding sites per protein subunit (n) and the apparent stability constant for complex formation (beta' Ca). These experiments were performed on unbuffered solutions, in either water or 0.01 M-KCl, to allow a determination of the number of hydrogen ions released per calcium ion bound (chi). The results indicate that near neutrality, the virus particle possesses two calcium ion binding sites per subunit having apparent stability constants greater than 10(4) M-1. The results are interpreted as if these two sites are non-identical and titrate independently. The higher affinity site for the virus in water has a value of log beta' Ca, which varies from about 8.5 at pH 8.5 to about 3.9 at pH 5.0, and for the virus in 0.01 M-KCl has a value that varies from about 6.2 at pH 8.0 to about 3.7 at pH 5.5. The higher affinity site for the virus in water binds up to two competing hydrogen ions, one with an apparent pKH value greater than 8.5 and the other with a value that varies from 6.0 at pH 5.5 to 7.3 at pH 8.0. For the virus in 0.01 M-KCl, only the competing hydrogen ion binding with an apparent pKH value greater than 8.5 remains. The results could be interpreted as indicating that the electrical charge on the virus particle has a constant value in the pH range 5.5 to 8.0 despite the fact that hydrogen ion titration curves for the intact virus particle indicate that the charge should vary from about -1 per subunit at pH 5.5 to about -4 at pH 8.0.

Binding Sites↗
PubMed1983

Calcium ion binding by isolated tobacco mosaic virus coat protein.

Calcium ion titrations were performed on solutions of tobacco mosaic virus coat protein using a calcium-specific ion-exchange electrode. Isolated coat protein was found incapable of binding calcium ions under equilibrium conditions at pH values above its iso-ionic point (pH 4.3 to 4.6). However, calcium ions were found to bind to coat protein under non-equilibrium conditions, which suggests that the isolated coat protein has the proper conformation to bind calcium ions at the iso-ionic point.

Binding Sites↗
PubMed1983

Calcium and potassium ion binding by tobacco mosaic virus ribonucleic acid.

Calcium and potassium ion titration experiments were performed on solutions of tobacco mosaic virus RNA using ion-specific electrodes. The data obtained were analyzed using Scatchard and Klotz plots for the number of binding sites per nucleotide (n), and the apparent stability constant for complex formation, beta Me. The experimental design also allowed for the determination of the number of protons released per metal ion bound, chi. The calcium ion titration in water yielded values of 0.45 for n, 6.03 for log beta Ca and 0.24 for chi. When this titration was repeated in 0.01 M-KCl, the values were found to be 0.11 for n, 5.08 for log beta Ca and zero for chi. An aqueous potassium titration was also performed, with values for n, log beta K and chi of 0.25, 2.96 and less than 0.10, respectively.

Binding Sites↗
PubMed1983

Polymerization of tobacco mosaic virus protein without and with hydrogen ion binding.

When tobacco mosaic virus (TMV) protein is polymerized at pH values above 7 in unbuffered solutions, either by raising temperature at constant ionic strength or by increasing ionic strength at constant temperature, a 20 S component is formed having bound only the very small amount of H+ ion supplied by the unpolymerized protein. When hydrogen ion is added by titration during polymerization so as to keep pH constant, as would occur automatically if a buffer were present, a 20 S component is formed with one H+ ion bound each for half of the subunits. Thus, a 20 S form with and a 20 S form without bound H+ ion exist. Furthermore, the 20 S form without bound H+ ion binds H+ ion when supplied by titration to produce a 20 S form with the same amount of bound H+ ion as when H+ ion is supplied during the polymerization.

Hydrogen Bonding↗
PubMed1982

Frederik B. Bang.

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History, 20th Century↗
PubMed1981

Scanning calorimetric investigation of the polymerization of the coat protein of tobacco mosaic virus.

The endothermic polymerization of the coat protein of tobacco mosaic virus has been studied by high-sensitivity differential scanning calorimetry, with control experiments involving turbidimetry and sedimentation velocity measurements. The variation of the apparent extent of polymerization under conditions close to equilibrium as the temperature is raised follows a course which is difficult to duplicate on the basis of simple models for the process. The enthalpy of polymerization at low protein concentration varies from 12.5 kcal (mol of monomer)-1 (17500 daltons) under conditions where the product is largely a mixture of short helical rods to 6.0 kcal ol-1 for the formation of double disks containing 34 monomer units. In the former case, the polymerization is accompanied by a decrease in apparent heat capacity of 350 cal K-1 mol-1 while in the latter there is an increase of 150 cal K-1 mol-1. These results constitute evidence that these two types of polymerization involve intersubunit bonds of quite different chemical character.

Calorimetry, Differential Scanning↗