Inverse Temperature Transition Research Articles

Solvent deuteration enhancement of hydrophobicity: DSC study of the inverse temperature transition of elastin-based polypeptides

As previously shown, the polypentapeptide of elastin, (Val{sup 1}-Pro{sup 2}-Gly{sup 3}-Val{sup 4}-Gly{sup 5}){sub n} or simply poly(VPGVG), undergoes an inverse temperature transition which is seen macroscopically as a phase separation with a dense viscoelastic phase of about 60% water, 40% peptide by weight and which is characterized molecularly by increase in intra- and intermolecular order as evidenced by formation of specific hydrophobic contacts. Furthermore, from an extensive study of polypentapeptides of the composition poly(f{sub x}(VPGXG), f{sub v}(VPGVG)), where f{sub x} + f{sub v} = 1 and X is any of the amino acid residues with apolar (hydrophobic) side chains, it has been shown that the temperature of the transition decreases and the heat of the transition increases with increased hydrophobicity. In the present paper differential scanning calorimetry has been utilized to determine the effect of D{sub 2}O on the temperature and heats of the inverse temperature transitions for poly(VPGVG), poly(IPGVG), poly(LPGVG), and poly(VPAVG) and in the latter case in the presence of 0.5 and 1.0 N NaCl and of 1,2, and 3 M urea. In all cases, the effect of D{sub 2}O as compared to H{sub 2}O is to lower the transition temperature about 2 C and to increase themore » heat of the transition about 10%, and this occurs also in the presence of NaCl, which itself lowers the temperature and increases the heat, and in the presence of urea, which itself raises the temperature and decreases the heat of the transition. It is concluded that the effect of replacement of H{sub 2}O by D{sub 2}O by D{sub 2}O in these polypeptides is to effect a small but consistent increase in the expression of hydrophobicity.« less

Pressure effect on inverse temperature transitions: biological implications

Elastic protein-based polymers of the form poly [ f x(VPGXG), f v(VPGVG)], where f x and f v are mole fractions with f x+ f v=1, exhibit inverse temperature transitions in the form of a phase separation in which folding and aggregation of polymer chains into more-ordered states of the condensed (coacervate) phase occurs on raising the temperature. When X = Trp, Phe or Tyr, an increase in pressure causes a substantial increase in the temperature of the transition. The data are interpreted to indicate that water molecules surrounding the aromatic side chains of Trp(W), Phe(F) or Tyr(Y) occupy less volume than water molecules in bulk water. The calculated volume change for poly[0.8(GVGVP), 0.2(GFGVP)], for example, on going from coacervate phase, where hydrophobic associations have largely eliminated waters of hydrophobic hydration, to be dispersed in water where the hydrophobic moieties are surrounded by water is 80 cm 3/mol of mean pentamers or some 400 cm 3/mol of (GFGVP). The results provide an understanding of the source of pressure effects in biological systems and for the capacity to design materials capable of exhibiting baromechanical transduction.

Phosphorylation and dephosphorylation modulation of an inverse temperature transition

Poly[15(IPGVG),(RGYSLG)], where RGYSLG is a protein kinase site, was synthesized. On raising the temperature of a 5 mg/ml solution, this polypeptide undergoes an inverse temperature transition at 18°C in which it folds into a contracted state by optimizing intramolecular hydrophobic interactions. Averaging the data of five experiments, phosphorylation by means of a 3′:5′ cyclic AMP dependent protein kinase to the extent of one phosphate in 360 residues raises the temperature of the folding transition to 32°C. The shift is completely reversed on dephosphorylation by alkaline phosphatase. Phosphorylation is hereby shown to be the most potent chemical perturbation known for shifting the temperature of an inverse temperature transition, which has been shown to be an efficient mechanism for achieving chemomechanical transduction (mechanochemical coupling).

Temperature of polypeptide inverse temperature transition depends on mean residue hydrophobicity

Temperature of polypeptide inverse temperature transition depends on mean residue hydrophobicity

Differential scanning calorimetry studies of NaCl effect on the inverse temperature transition of some elastin‐based polytetra‐, polypenta‐, and polynonapeptides

Differential scanning calorimetry studies of the effect of NaCl on protein-based polymer self-assembly has been carried out on six elastin-based synthetic sequential polypeptides--i.e., the polypentapeptide (L-Val1-L-Pro2-Gly3-L-Val4-Gly5)n and its more hydrophobic analogues (L-Leu1-L-Pro2-Gly3-L-Val4-Gly5)n and (L-Val1-L-Pro2-L-Ala3-L-Val4-Gly5)n; the polytetrapeptide (L-Val1-L-Pro2-Gly3-Gly4)n and its more hydrophobic analogue (L-Ile1-L-Pro2-Gly3-Gly4)n; and the polynonapeptide (a pentatetra hybrid), (L-Val1-L-Pro2-Gly3-L-Val4-Gly5-L-Val6-L-Pro7-Gly8-Gly9++ +)n. Previous physical characterizations of the polypentapeptides have demonstrated the occurrence of an inverse temperature transition since increase in order of the polypentapeptide, as the temperature is raised from below to above that of the transition, has been repeatedly observed using different physical characterizations. In the present experiments, it is observed that the transition temperatures of the polypeptides studied are linearly dependent on NaCl concentration. The molar effectiveness of NaCl in shifting the transition temperature delta Tm/[N], is about 14 degrees C/[N], with the dependence on peptide hydrophobicity being fairly small. Interestingly, however, the delta delta Q/[N] does depend on the hydrophobicity of a polypeptide.

?-Spiral conformations of the elastomeric polytetrapeptides, (VPGG)n and (IPGG)n, by 2DNMR and molecular mechanics studies

The synthetic polytetrapeptide using the repeating sequence VPGG found in the fibrous protein, elastin, exhibits a reversible inverse temperature transition, i.e., the molecular order increases on raising the temperature of the polypeptide in aqueous solutions. The matrices formed from the coacervate by γ-irradiation-induced cross-linking exhibit an elastic modulus and temperature dependence of elastomeric force with similarity to that of fibrous elastin. As demonstrated on poly(VPGVG), which forms a β-spiral structure with recurring Type II β-turns, the molecular structure of the elastin-based polypeptides is fundamental to an understanding of the mechanism of elasticity. It was found previously that the repeating unit VPGG in the polytetrapeptide forms a Type II β-turn with a hydrogen bond between Val1 CO and Gly4 NH. This secondary structural feature is confirmed in this report by 2D NMR data as indicated by specific NOE cross-peaks, particularly, dNN(3,4), dαN(2,3), dαN(2,4), and dγN(1,4). The same secondary structural feature is found in the 2D NMR data for its analog polypeptide, poly(IPGG). The NMR data provide conclusive evidence for the Type II β-turn secondary structure. Molecular mechanics computations were performed to develop a more detailed tertiary structure for the polytetrapeptides. The ECEPP/2 potential field and build-up strategy were employed in mapping conformational space of VPGG and its high polymer. In addition, helical structures are sought using the Go–Scheraga condition, on the assumption that the repeated sequence would preferentially adopt a helical or nearhelical conformation on optimization of intramolecular hydrophobic contacts. A number of structures with helically recurring β-turns was obtained and can be used as starting structures in future studies that are to include hydration. The structures were also evaluated in terms of potential energy using the CHARMm force field.

Differential scanning calorimetry studies of the inverse temperature transition of the polypentapeptide of elastin and its analogues

Differential scanning calorimetry studies have been carried out on the sequential polypeptide of elastin, (L-Val1-L-Pro2-Gly3-L-Val4-Gly5)n, abbreviated as PPP, and its more hydrophobic analogues (L-Leu1-L-Pro2-Gly3-L-Val4-Gly5)n, referred to as Leu1-PPP, and (L-Ile1-L-Pro2-Gly3-L-Val4-Gly5)n, referred to as Ile1-PPP Consistent with inverse temperature transitions, the temperatures of the transitions for which maximum heat absorption occurs are inversely proportional to the hydrophobicities of the polypentapeptides (31 degrees C for PPP, 16 degrees C for Leu1-PPP, and 12 degrees C for Ile1-PPP), and the endothermic heats of the transitions are small and increase with increasing hydrophobicity, i.e., 1.2, 2.9, and 3.0 kcal/mol pentamer for PPP, Leu1-PPP, and Ile1-PPP, respectively. Previous physical characterizations of the polypentapeptides have demonstrated the occurrence of an inverse temperature transition since increase in order, as the temperature is raised above that of the transition, has been repeatedly observed using different physical characterizations. Furthermore, the studies demonstrated identical conformations for PPP and Il21-PPP above and below the transition. Both heats and temperatures of the transitions vary with hydrophobicity, but not in simple proportionality.

Cyclododecapeptide analog of the polyhexapeptide of elastin: 2-D NMR and molecular dynamics studies

The hexapeptide, (APGVGV), is one of the repeating sequences found in the natural protein, elastin. The cyclododecapeptide, cyclo( L-Ala ’-~-Pro~-Gly’-~-Val 4-Gly5-~-Va16)2, was synthesized and was found to undergo an inverse temperature transition leading to crystallization. Extensive NMR experiments have been carried out previously to evaluate its secondary structure in comparison to that of its linear counterpart, polyhexapeptide ( APGVGV),, directly and in terms of the concept of cyclic conformations with linear conformational correlates. Building on the previous work, this report adds 2-D NMR and molecular dynamics studies on the molecular structure of the cyclododecapeptide. From the 2-D COSY and 2-D NOESY experimental results, a reversal of the previous Gly’ and Gly’ resonance assignments in the cyclododecapeptide is reported. And in the 2-D NOESY study, a prominent NOE is found between the NH’s of the two valine residues at position 4 and 6. Because the Val4 and Val6 residues are not adjacent to each other sequentially, the proximity ofthese two backbone hydrogens is used as an imposed constraint in constructing the molecular Structure of the cyclododecapeptide. Molecular dynamics investigations were employed using the information from the 1-D and 2-D NMR experiments to arrive at potential molecular structures of the cyclododecapeptide. The characteristic secondary structural feature obtained is the expected Type 11 Pro2-Gly3 D-turn consisting of the 10-membered hydrogen bond between the residue-4 NH and the residue-1 C=O, a feature previously found in this and all other repeating peptides in elastin which contain the Pro2-Gly3 sequence.

Synthesis of 4% Glu-containing Val1 and Ile1-polypentapeptides: Model protein systems for demonstrating mechanochemical coupling

The synthesis of 4% Glu-polypentapeptide (PPP) (i.e., 4 Glu residues per 100 amino acid residues) and 4% Glu-Ile1-PPP, in which Val1 is substituted by a more hydrophobic Ile residue, is carried out by copolymerizing the p-nitrophenyl-active esters of GE(OMe)GVP and GE(OMe)GIP with their parent pentamers GVGVP and GVGIP in 1:4 ratios, respectively. After removal of the methyl ester on the side chain of Glu, these polymers exhibited a remarkable pH dependence of the temperature for their inverse temperature transitions, which are followed as turbidity development at 300 nm. On gamma-irradiation crosslinking, the elastomeric bands obtained exhibited a pH-mediated contraction and relaxation. Thus, for the first time, mechanochemical coupling is demonstrated in a synthetic polypeptide system. That the basic mechanism involves the hydrophobic effect (chemical modulation of an inverse temperature transition) and not ion-ion electrostatic repulsion is also discussed.

Elastomeric Polypeptide Biomaterials: Structure and Free Energy Transduction

AbstractThe primary, secondary, tertiary and quaternary structures are presented and discussed for elastomeric polypeptides capable of undergoing inverse temperature transitions, that is, these polypeptides fold with the extrusion of water on raising the temperature through a transition. The elastomeric polypeptides, which are comprised of repeating peptide sequences, appear to be dominantly entropic elastomers. As these elastomers exhibit preferred secondary, tertiary and quarternary structure, they are not properly characterized as the random chain networks commonly ascribed to entropic elastomers. Instead, a mechanism of damping of internal chain dynamics on extension is described and referred to as the librational entropy mechanism of elasticity. Indeed, there are emerging a set of structural concepts for elastomeric polypeptides.Of particular interest is that these elastomers are capable of exhibiting free energy transduction, e.g., thermomechanical and chemomechanical. A principle is stated for thermomechanical transduction and a postulate is given for chemomechanical transduction which is supported by prediction and experimental verification. The underlying mechanism is considered to be an aqueous(hydration) mediated apolar(hydrophobic)-polar interaction free energy which arises out of a competition between apolar and polar groups for limited waters of hydration. In general, there emerges a simple structural perspective of free energy transduction in elastomeric polypeptide biomaterials that involves thermal, mechanical or chemical means of altering the equilibrium between folded and unfolded states, where the folded states are dynamic helices called β-spirals with dominantly hydrophobic intramolecular interturn contacts and the unfolded states have the hydrophobic groups exposed to water.

Chemical potential driven contraction and relaxation by ionic strength modulation of an inverse temperature transition

Chemical potential driven contraction and relaxation by ionic strength modulation of an inverse temperature transition

Mechanochemical coupling in synthetic polypeptides by modulation of an inverse temperature transition.

For the polypentapeptide of elastin, (L-Val-L-Pro-Gly-L-Val-Gly)n, and appropriate analogs when suitably cross-linked, it has been previously demonstrated that development of elastomeric force at fixed length and length changes at fixed load occur as the result of an inverse temperature transition, with the temperature of the transition being inversely dependent on the hydrophobicity of the polypeptide. This suggests that at fixed temperature a chemical means of reversibly changing the hydrophobicity could be used for mechanochemical coupling. Evidence for this mechanism of mechanochemical coupling is given here with a 4%-Glu-polypentapeptide, in which the valine in position 4 is replaced in 1 out of 5 pentamers by a glutamic acid residue. Before cross-linking, the temperature for aggregation of 4%-Glu-polypentapeptide is remarkably sensitive to pH, shifting from 25 degrees C at pH 2 to 70 degrees C at pH 7.4 in phosphate-buffered saline (PBS). At 37 degrees C, the cross-linked 4%-Glu-polypentapeptide matrix in PBS undergoes a pH-modulated contraction and relaxation with a change from pH 4.3 to 3.3 and back. The mean distance between carboxylates at pH 4.3 in the elastomeric matrix is greater than 40 A, twice the mean distance between negatively charged species in PBS. Accordingly, charge-charge repulsion is expected to make little or no contribution to the coupling. Mechanochemical coupling is demonstrated at fixed load by monitoring pH dependence of length and at constant length by monitoring pH dependence of force. To our knowledge, this is the first demonstration of mechanochemical coupling in a synthetic polypeptide and the first system to provide a test of the recent proposal that chemical modulation of an inverse temperature transition can be a mechanism for mechanochemical coupling. It is suggested that phosphorylation and dephosphorylation may modulate structure and forces in proteins by locally shifting the temperatures of inverse temperature transitions.

Entropic elastic processes in protein mechanisms. II. Simple (passive) and coupled (active) development of elastic forces.

The first part of this review on entropic elastic processes in protein mechanisms (Urry, 1988) demonstrated with the polypentapeptide of elastin (Val1-Pro2-Gly3-Val4-Gly5)n that elastic structure develops as the result of an inverse temperature transition and that entropic elasticity is due to internal chain dynamics in a regular nonrandom structure. This demonstration is contrary to the pervasive perspective of entropic protein elasticity of the past three decades wherein a network of random chains has been considered the necessary structural consequence of the occurrence of dominantly entropic elastomeric force. That this is not the case provides a new opportunity for understanding the occurrence and role of entropic elastic processes in protein mechanisms. Entropic elastic processes are considered in two classes: passive and active. The development of elastomeric force on deformation is class I (passive) and the development of elastomeric force as the result of a chemical process shifting the temperature of a transition is class II (active). Examples of class I are elastin, the elastic filament of muscle, elastic force changes in enzyme catalysis resulting from binding processes and resulting in the straining of a scissile bond, and in the turning on and off of channels due to changes in transmembrane potential. Demonstration of the consequences of elastomeric force developing as the result of an inverse temperature transition are seen in elastin, where elastic recoil is lost on oxidation, i.e., on decreasing the hydrophobicity of the chain and shifting the temperature for the development of elastomeric force to temperatures greater than physiological. This is relevant in general to loss of elasticity on aging and more specifically to the development of pulmonary emphysema. Since random chain networks are not the products of inverse temperature transitions and the temperature at which an inverse temperature transition occurs depends on the hydrophobicity of the polypeptide chain, it now becomes possible to consider chemical processes for turning elastomeric force on and off by reversibly changing the hydrophobicity of the polypeptide chain. This is herein called mechanochemical coupling of the first kind; this is the chemical modulation of the temperature for the transition from a less-ordered less elastic state to a more-ordered more elastic state. In the usual considerations to date, development of elastomeric force is the result of a standard transition from a more-ordered less elastic state to a less-ordered more elastic state.(ABSTRACT TRUNCATED AT 400 WORDS)

Free energy (chemomechanical) transduction in elastomeric polypeptides by chemical potential modulation of an inverse temperature transition

Data and analyses are presented on the first synthetic polypeptide system to exhibit mechanochemical coupling; the mechanochemical coupling can also be demonstrated to be both polymer-based and solvent-based with respect to where the result of the change in the chemical potential is focused. Both polymer-based and solvent-based processes are the result of chemomechanical transduction in which the change in chemical potential results in a change in the temperature at which an inverse temperature transition occurs. In the polymer-based process, the contraction/relaxation occurs due to a change in the chemical nature of the polypeptide; in the solvent-based process there is no change in the chemical nature of the polypeptide on contraction or relaxation, but rather the change in chemical potential changes the state of hydration of the polypeptide. The new mechanochemical system provides an experimental system with which to clarify and to quantitate what may be called aqueous mediated apolar–polar interaction energies in polypeptides and proteins with hydrophobic groups that may be variously exposed to the aqueous solution or buried within the folded polypeptide or protein. Furthermore, it is noted that any conformational change exhibited by a polypeptide or protein that is the result of a binding of a chemical moiety, the change in chemical nature of a bound moiety or the change in chemical potential of the medium can be viewed in terms of mechanochemical coupling or chemomechanical transduction.

Entropic elastic processes in protein mechanisms. I. Elastic structure due to an inverse temperature transition and elasticity due to internal chain dynamics.

Numerous physical characterizations clearly demonstrate that the polypentapeptide of elastin (Val1-Pro2-Gly3-Val4-Gly5)n in water undergoes an inverse temperature transition. Increase in order occurs both intermolecularly and intramolecularly on raising the temperature from 20 to 40 degrees C. The physical characterizations used to demonstrate the inverse temperature transition include microscopy, light scattering, circular dichroism, the nuclear Overhauser effect, temperature dependence of composition, nuclear magnetic resonance (NMR) relaxation, dielectric relaxation, and temperature dependence of elastomer length. At fixed extension of the cross-linked polypentapeptide elastomer, the development of elastomeric force is seen to correlate with increase in intramolecular order, that is, with the inverse temperature transition. Reversible thermal denaturation of the ordered polypentapeptide is observed with composition and circular dichroism studies, and thermal denaturation of the crosslinked elastomer is also observed with loss of elastomeric force and elastic modulus. Thus, elastomeric force is lost when the polypeptide chains are randomized due to heating at high temperature. Clearly, elastomeric force is due to nonrandom polypeptide structure. In spite of this, elastomeric force is demonstrated to be dominantly entropic in origin. The source of the entropic elastomeric force is demonstrated to be the result of internal chain dynamics, and the mechanism is called the librational entropy mechanism of elasticity. There is significant application to the finding that elastomeric force develops due to an inverse temperature transition. By changing the hydrophobicity of the polypeptide, the temperature range for the inverse temperature transition can be changed in a predictable way, and the temperature range for the development of elastomeric force follows. Thus, elastomers have been prepared where the development of elastomeric force is shifted over a 40 degrees C temperature range from a midpoint temperature of 30 degrees C for the polypentapeptide to 10 degrees C by increasing hydrophobicity with addition of a single CH2 moiety per pentamer and to 50 degrees C by decreasing hydrophobicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Dielectric relaxation studies on analogs of the polypentapeptide of elastin

Abstract : Dielectric measurements of the complex permittivity of coacervate concentrations of two analogs of the polypentapeptide of elastin, were taken over the frequency range of 1 MHz to 1000 MHz and over the temperature range of 0 to 60 C. Two relaxation processes were observed in each polypentapeptide. One with a frequency centered in the low MHz frequency range which has been attributed to a low frequency librational mode within the polypeptide. The other relaxation is located near the GHz frequency range. The magnitude of the dielectric increment of the librational mode of each polypentapeptide analog increases with increasing temperature from near zero at 0 c to approximately 40 at 60 C, showing an inverse temperature transition to a more-ordered structure. Conversely the magnitudes of the dielectric increment of the high frequency relaxation decrease on increasing the temperature and differ in approximate proportion to the hydrophobicity of the pentamer for the polypentapeptide of elastin and the two analogs at temperatures below the inverse temperature transition. It is suggested that clathrate-like water surrounding hydrophobic side chains contributes to the high frequency relaxation.

Entropic elastomeric force in protein structure/function

Briefly noting earlier studies on the polypentapeptide of elastin, (Val1-Pro2-Gly3-Val4-Gly5)n, and on elastin, it is emphasized that entropic elastomeric force can be exhibited by nonrandom, anisotropic polypeptide systems and therefore that entropic elastomeric force does not necessarily result from isotropic random chain networks as required by the classical theory of rubber elasticity, nor does it result from solvent entropy effects as deduced from the slow loss of elastomeric force on thermal denaturation. Instead entropic protein elasticity can be the result of internal chain dynamics, specifically of librational processes that become damped on chain extension. This new mechanism of entropic protein elasticity allows for an understanding not only of elastin but also of the passive tension of striated muscle, of the voltage-dependent interconversion between open and closed conductance states in the sodium channel of squid nerve, and of protein elastic forces producing strain in a substrate bond during enzyme catalysis. Because entropic elastomeric force develops as a result of an inverse temperature transition, it becomes possible to shift the temperature of the transition to higher or lower temperatures by decreasing or increasing, respectively, the hydrophobicity of the elastomeric polypeptide chain. In warm-blooded animals this allows for biochemical modulation of the relaxation or development of entropic elastomeric force by an enzymatically modulated decrease or increase of the hydrophobicity, as for example, by phosphorylation or dephosphorylation of the elastomeric polypeptide chain. This understanding provides a mechanism for modulating protein function, whether for example enzymatic or channel, a mechanism for the remarkable reversible structural processes that attend parturition, and a mechanism for the connective tissue anomalies of wound repair and enviromentally induced lung disease.

Polytetrapeptide of elastin

High molecular weight polytetrapeptide of elastin, (L.Val1-L.Pro2-Gly3-Gly4)n, was synthesized using activation of the (GGVP) permutation for polymerization. The temperature-dependence of aggregation was characterized as a function of concentration and the circular dichroism spectra were obtained in the 20 degrees to 70 degrees C temperature range. The latter showed an inverse temperature transition centered near 50 degrees C in which polypeptide order increased on raising the temperature. A concentration of 0.6 g of polytetrapeptide in 1 g of water was gamma irradiation cross-linked (20 Mrad) to form an elastomeric matrix. A study of the temperature-dependence of elastomeric force demonstrated a transition toward increased force on raising the temperature with a midpoint of the transition near 50 degrees C. Thus, there is a correlation between increase in intramolecular order and elastomeric force development. These results are compared to previous results on the polypentapeptide of elastin, (VPGVG)n and on an analog, (IPGVG)n, to demonstrate that the temperature of the transition is proportional to the hydrophobicity of the repeating unit. The point is noted that the elastomeric force development correlates better with intramolecular ordering than with intermolecular processes.

Temperature-correlated force and structure development in elastomeric polypeptides: the Ile1 analog of the polypentapeptide of elastin.

AbstractThe Ile1 analog of the polypentapeptide of elastin, (L · Ile1‐L · Pro2‐Gly3‐L · Val4‐Gly5)n, abbreviated as Ile1‐PPP, was synthesized with n > 100 to determine the effect of the increased hydrophobicity of the pentamer resulting from Val1 replacement by Ile1 on the previously characterized inverse temperature transition of the polypentapeptide of elastin (PPP). Ile1‐PPP, dissolved in water at 4°C, was found to aggregate, forming a viscoelastic coacervate on raising the temperature. The onset of aggregation was 8°C for Ile1‐PPP, as compared to 24°C for PPP. Characterization by CD demonstrated an increase in intramolecular order on raising the temperature from 8°C to 25°C, and demonstrated similar conformations for PPP and Ile1‐PPP before and after their respective transitions. The CD‐characterized transition also occurred at a temperature some 15°C lower than that of PPP. By means of 20‐Mrad γ‐irradiation cross‐linking of the Ile1‐PPP coacervate, an elastomeric matrix was formed with an elastic modulus, similar to that of 20‐Mrad cross‐linked PPP. The temperature dependence of elastomeric force of cross‐linked Ile1‐PPP showed an abrupt increase from essentially zero at 8°C to three‐quarters of full force at 10°C and essentially full force by 20–25°C. This development of elastomeric force for the more hydrophobic Ile1‐PPP matrix, which parallels the increase in intramolecular order characterized by the CD studies, also occurs at a temperature some 15°C lower than that for the PPP matrix. Thus, in these elastomeric polypeptides, development of elastomeric force is coupled to an inverse temperature transition, the temperature of which depends inversely on the hydrophobicity of the constituent pentamer. It appears that a series of elastomeric polypeptide biomaterials are possible in which the temperature over which elastomeric force develops can be varied.

Carbon-13 NMR relaxation studies demonstrate an inverse temperature transition in the elastin polypentapeptide.

Carbon-13 NMR longitudinal relaxation time and line-width studies are reported on the coacervate concentration (about 60% water by weight) of singly carbonyl carbon enriched polypentapeptides of elastin: specifically, (L-Val1-L-[1-13C]Pro2-Gly3-L-Val4-Gly5)n and (L-Val1-L-Pro2-Gly3-L-Val4-[1-13C]Gly5)n. On raising the temperature from 10 to 25 degrees C and from 40 to 70 degrees C, carbonyl mobility increases, but over the temperature interval from 25 to 40 degrees C, the mobility decreases. The results characterize an inverse temperature transition in the most fundamental sense of temperature being a measure of molecular motion. This transition in the state of the polypentapeptide indicates an increase in order of polypeptide on raising the temperature from 25 degrees C to physiological temperature. This fundamental NMR characterization corresponds with the results of numerous other physical methods, e.g., circular dichroism, dielectric relaxation, and electron microscopy, that correspondingly indicate an increase in order of the polypentapeptide both intramolecularly and intermolecularly for the same temperature increase from 25 to 40 degrees C. Significantly with respect to elastomeric function, thermoelasticity studies on gamma-irradiation cross-linked polypentapeptide coacervate show a dramatic increase in elastomeric force over the same interval that is here characterized by NMR as an inverse temperature transition. The temperature dependence of mobility above 40 degrees C indicates an activation energy of the order of 1.2 kcal/mol, which is the magnitude of barrier expected for elasticity.