The titration curves of protein fibres

Lloyd, Dorothy Jordan; Bidder, P. Betty

doi:10.1039/tf9353100864

Cited by 14 publications

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“…The assumption of an unfolding mechanism for the multilaminar proteins, however, implies th at a molecular sheet or ribbon is formed, the in dividual polypeptide chains of which are linked by, for example, dithio bonds. True fibre formation would be possible by prior or subsequent rupture of the, dithio and similar linkings and, with respect to blood-fibrinogen, interest in such a possibility is enhanced by consideration of the recent conclusion of Lyons (1945) th at the thrombase system contains a component capable of doing this, together with the earlier observations of B arrett (1920) on the filamentous nature of fibrin. A final point of interest concerns the solubility of the degradation products afforded by enzyme-or acid-hydrolysis of fibroin, a question th at at present is being further investigated.…”

Section: Chrmentioning

confidence: 99%

Studies on silk proteins I. The properties and constitution of fibroin. The conversion of fibroin into a water-soluble form and its bearing on the phenomenon of denaturation

Coleman¹,

Howitt²

1947

Proc. R. Soc. Lond. A

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[Plate 5]Some of the constituent amino-acids of fibroin (degummed silk) are determined. Special attention is directed to histidine, owing to its use in the calculation of the molecular weight of fibroin. A value of 0*45 % has been found by methods in which the histidine is isolated as nitranilate or di-(3:4-dichlorobenzenesulphonate). Other values obtained are serine 12*6%, threonine 1-5 %, tyrosine 10*6 %, and proline 1*5 %. Hydroxyproline appears to be absent, but the presence of small amounts of some hydroxyamino-acid other than serine and threonine is indicated.The mean residue weight of fibroin is determined by three methods, one of which is a new method based on analysis of the complex formed between fibroin and cupri-ethylenediamine. This method gives a Cu:fibroin-N ratio of 1: 1*92 and, if allowance is made for co-ordination with the tyrosine hydroxyl group, an equivalence of 1*964 atoms of peptide-nitrogen to 1 atom of copper is obtained. The three methods give an average value of 78*0 for the mean residue weight of fibroin. This value, together with the most acceptable data for amino-acid constituents, indicate that the unidentified anhydro-residues (about 20%) have a mean residue weight of about 107.Evidence is presented that fibroin contains no amide-nitrogen. Methods for the deter mination of amide-nitrogen at present in use, which indicate a content of 1 to 2 %, are considered to be unreliable.Fibroin dissolved in cupri-ethylenediamine gives, on neutralization and dialysis of the resulting solution, a water-soluble protein. The production of this water-soluble protein is attended by little or no degradation of the original fibroin as shown by determinations of fluidity, amino-nitrogen, and acid-and alkali-combining power.The water-soluble protein is precipitated by the normal protein-precipitating reagents, but in every instance examined the precipitated material exhibits an insolubility com parable with that of the original fibroin.Factors responsible for the solubilization process are investigated and data for molecular weight, titration values, ultra-violet absorption spectra, reducing activity, optical rotation, tryptic hydrolysis, and viscosity for both soluble and dispersed fibroin are given. Soluble fibroin has [a]^5 -53*1° and dispersed fibroin [a]*® -58*9°, both in aqueous media.The preparation and properties of films and filaments of fibroin are described. Films of fibroin can be prepared that are water-soluble. On stretching, these films show strainbirefringence, acquire considerable tensile strength, and become insoluble in water, but X-ray examination gives the /?-keratin pattern for both the stretched and unstretched films.Reasons are advanced for considering the water-soluble form of fibroin to be the native or renatured protein and the original protein to be the denatured form.The denaturation of fibroin is discussed on the basis that denaturation is essentially an unfolding of a coiled long-chain molecule. The subsequent aggregation of the uncoiled molecules to give an insoluble pr...

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Section: Chrmentioning

confidence: 99%

Studies on silk proteins I. The properties and constitution of fibroin. The conversion of fibroin into a water-soluble form and its bearing on the phenomenon of denaturation

Coleman¹,

Howitt²

1947

Proc. R. Soc. Lond. A

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“…The examination of measurements reported by Speakman and Hirst [43], 3 Lloyd and Bidder [34], and others leads to the conclusion that the titration curves of these three proteins, determined in the absence of salt, are distinguished from those of all soluble proteins so far studied 4 under the same conditions in three principal respects:…”

Section: Introductionmentioning

confidence: 99%

“…additional factors must be taken into account. A possible clue to the nature of the difference is suggested by the fact that the steeper slope characterizing the curves for the insoluble proteins may be described to a good degree of approximation by substituting (H+) 2 for (H+) in the mass law expression for egg albumin used by Cannan. It seems likely that these differences, characteristic not only of wool but of other high-molecular insoluble proteins as well [34], are necessarily associated with the presence of a separate phase. Nevertheless, many proteins which are relatively insoluble at their isoelectric points have hitherto been titrated in the presence of much undissolved material over at least part of the total range of the titration.…”

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“…Among those who have recognized the existence of these differences between the titration curves of dissolved and undissolved proteins, Speakman and his collaborators [43,44,45] and Lloyd and Bidder [34], have preferred to attribute them to fundamental differences between the structures of insoluble and soluble oroteins rather than to factors introduced by the existence of two-phase equilibria. Thus Speakman appears to believe that salt linkages, between acidic and basic groups, prevent the functioning of these groups in their customary ranges of acidity because certain minimal acid or base concentrations must be exceeded before such salt linkages are broken.…”

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Combination of wool protein with acid and base: hydrochloric acid and potassium hydroxide

Steinhardt¹,

Harris²

1940

J. RES. NATL. BUR. STAN.

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As an initial part of a general program for the study of the acidic and basic characteristics of textile fibers, a study has been made of the dependence on pH of the amounts of hydrochloric acid and of potassium hydroxide taken up by wool from aqueous solutions. The effect on this dependence of the maintenance of a constant ionic strength by additions of a neutral salt, potassium chloride, has also been determined. Most of the measurements were made at 0° C to minimize the effects of decomposition brought about by exposure to extreme concentrations of acid or base.The maximum acid-binding capacity, independent of ionic strength, is 0.82 millimole per gram; the maximum base-binding capacity is greater than 0.78 millimole. With salt absent, no appreciable binding of acid or base occurs in the pH interval, 5 to 10, but the amount bound increases very sharply as these limits are exceeded. When salt is present, the amount of acid or base bound changes with pH more gradually, and there is no wide region in which combination fails to occur; the point of zero combination is sharply defined and is near pH 6.4. The positions of the titration curves with respect to the pH axis are different at every ionic strength. The differences are larger than can be attributed to the effect of salts on the dissociation of acids; thus, in dilute solutions an n-fold change in the total concentration of chloride ions produces a change almost as great as would be produced by a similar n-fold change in the concentration of hydrogen ions. This approach to stoichiometric dependence of the acid bound on the concentration of anions as well as of hydrogen ions accounts for the greater steepness of the titration curve when the source of both ions is the acid alone.The dependence of acid bound on anion concentration or base bound on concentration of cations is explained by treating the electrostatic restrictions arising from the existence of two phases as a case of partial dissociation of protein salts. A possible alternative analysis by means of the Donnan equilibrium is also presented, and factors to be considered in making a final choice between the two treatments are described in detail. Either analysis predicts that the positions of the curves wi, th res~t to the pH axis should, at high salt concentrations, approach a limit which should correspond to the titration curve of the same protein in the dissolved state. This prediction is supported by the fact that the data for wool agree very closely at high salt concentrations with those for a similar but soluble protein, egg albumin.On the basis of this comparison, a detailed analysis is undertaken of the composition of the titration curve in terms of the constituent di-acidic and di-basic amino acids of wool. This analysis leads to the conclusion that the binding of acid and base by wool occurs at the free carboxyl, imidazole, amino, and guanidino groups, but that no combination of base with the tyrosine hydroxyl group takes place in the pH range of this investigation.I The state of comb...

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“…The manner in which the titration curves of the insoluble proteins, and especially of wool, differ from those of the soluble proteins has been discussed by Speakman and Hirst [1], 2 by Lloyd and Bidder [2] 1 Research Associates at the National Bureau of Standards, representing the Textile Foundation. , Figures in brackets indicate the literature references at the end of this paper.…”

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Combination of silk fibroin with acid and with base

Gleysteen¹,

Harris²

1941

J. RES. NATL. BUR. STAN.

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A study was made of the dependence on pH of the amounts of hydrochloric acid and of potassium hydroxide that are taken up by silk fibroin at 0° C. The effect of added potassium chloride on this dependence was also investigated, and was shown to be the binding of an increased quantity of acid or base at a given pH.The maximum acid-combining capacity of silk fibroin is 0.13 milliequivalent per gram; the maximum base-binding capacity is greater than 0.90 milliequivalent per gram. The presence of 0.13 to 0.17 milliequivalent of free carboxyl groups in silk fibroin is estimated from the titration curve. The great amount of base bound can be accounted for only if the phenolic hydroxyl groups of tyrosine take part in the equilibria with base. Further evidence that these groups bind base is provided by the greatly decreased amount of base bound by methylated fibroin. CONTENTS Page

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The titration curves of protein fibres

Cited by 14 publications

References 0 publications

Studies on silk proteins I. The properties and constitution of fibroin. The conversion of fibroin into a water-soluble form and its bearing on the phenomenon of denaturation

Studies on silk proteins I. The properties and constitution of fibroin. The conversion of fibroin into a water-soluble form and its bearing on the phenomenon of denaturation

Combination of wool protein with acid and base: hydrochloric acid and potassium hydroxide

Combination of silk fibroin with acid and with base

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