The association reaction of collagen model polypeptides (Pro‐Pro‐Gly)_n

Abstract

SynopsisThe characterization of recently synthesized (Pro-Pro-Gly),, n = 7 , s is described, along with melting profile studies of its association equilibrium, and thermal quenching studies of the kinetics of its association reaction. The order of the kinetic reaction is about 3, implying that three peptide chains are involved in the activated state of the rate-limiting step. The reaction rate was found to exhibit a negative temperature coefficient. With the (Pro-Pro-Gly)7 peptide, the concentration dependence of the (Pro-Pro-Gly), association equilibrium was observed for the first time.Detailed thermodynamic analysis for these n = 7, 8 data, together with literature data for n = 10, 15,20 were carried out for both the simple "all-or-none" binding model and for a series of complex equilibrium models. For the latter, all of the (Pro-Pro-Gly), data (in 10% acetic acid) are fit best with a maximally cooperative near-neighbor model with a standard enthalpy change AH = -650 cal/mole of residues, and a standard entropy change A S = -14.63 -.10/n cal/deg-mole of residues, wherein the -10 eu represents an end-effect contribution to the binding free energy.With regard to optical rotatory properties and thermodynamic parameters, the data for the new n = 7, 8 peptides match rather well with the literature data for the n = 10, 15, and 20 peptides.The enthalpic stabilization per residue of the triple-helical form of (Pro-Pro-Gly), was nearly an order of magnitude smaller than the enthalpic stabilization per additional proline obtained from diwct calorimetric measurements on native collagens of different (and much lower) proline contents by Privalov and Tiktopulo. [Biopolyrners (1970) 9, 127-139.1 Possible explanations for this phenomenon are discussed.

Investigation of the formation of triple helices between (pro‐pro‐gly)n's of different degrees of polymerization using gel filtration

“…Partly, the inadequacy of the model stemmed from the neglect of the effect of terminal residues which should contribute differently to the stability of the triple helix as compared to the interior residues. 16 When we compare the theoretically predicted results with the observed values, we have to take into account one more experimental fact, Figure 1 shows that the transition curve of the highest concentration (C, = 1.32%) is rather different from the others. Its [a1578 a t lower and higher temperature regions is distinctly larger than those of others.…”

“…The quantitative studies of the kinetics of helix formation of (Pro-Pro-Gly), were made by Sutoh and Nodal8 and Shaw and Schurr. 16 The half-time of the helix formation is of the order of 1 hr, in which the concentration and the temperature are 3 mg/ml and 15°C for (Pro-Pro-Gly)lS. indicate coils of (Pro-Pro-Gly),, and (Pro-Pro-Gly),o, triple helices of (Pro-Pro-Gly),,?…”

“…[14][15][16] As Schwarz and Poland analyzed,14 the all-or-none-like behavior of the transition deviates as the degree of polymerization, n , increases. In Table I, the results of the numerical calculations are also listed using the enthalpy change AH, = -7.4 kcal/mol and the entropy change ASu = -20 e.u.…”

Conformations of different gelatins in solutions and in films an analysis of circular dichroism (CD) measurements

“…Numerous investigations of helix-random coil transitions and estimatons of helix contents were performed by measurements of optical rotation at a wavelength outside the characteristic bands [2,22,[51][52][53][54][55][56][57]. Because measurements in the region of an optical active absorption band give greater, more precise informarion, we have performed CD measurements in the wavelength range of the characteristic spectrum of the collagen triple helix.…”

Higher order structure of (1,3)‐β‐D‐glucans and its influence on their biological activities and complexation abilities

“…The imperfectly organized regions might be duplex segments, where the third chain makes a loop that subsequently merges into the triplex, or three chains strand separated in individual sequences. The average length of the triplex parts corresponding to the cooperative length can be obtained from the partition function with the appropriate thermodynamic parameters 36, 59, 60. The repeating primary structure opens for imperfect matching in the structure, resulting in loop formation.…”