Mixed monolayers of polypeptides

Abstract

Mixed monolayers of two polypeptides, poly-F-methyl-L-glutamate and poly-L-alanine, in the same ce-helix surface conformation, were studied at the water/air interface.From a comparison of the experimental n-A isotherms with Hugglns' theory and from the examination of the MIR spectra for the two components and their mixtures, it was possible to deduce that poly-y-methyl-L-glutamate and poly-L-alanine were totally miscible at the surface with prevalently attractive interactions and that the mixtures maintained the conformation of the two components.The low values of the interaction parameters, deduced by applying Joos' theory to the collapse pressures of the mixtures, demonstrated that the interactions were prevalently hydrophobic.

Polypeptides mixed monolayers: collapse mechanism

“…As can be easily noted, the collapse pressure varied as the molar ratios varied; this has been previously reported [2] and agrees with miscibility in monolayers. Since the contemporary separation of the two polypeptides seemed to be possible, in order to have information concerning miscibility in the collapsed phase, the respective compositions of the two polypeptides in the collapsed phase were calculated by applying theJoos theory [14] and using the determined ,c values of the components and the mixtures and of already obtained [2] values of the interaction factors. In particular, it can be noted that the richest mixture of I~MG had a zone with an arrest nearly independent of the characteristic zone of PTMG whereas the richest mixture of PLA had, in the same zone, a longer inflection typical of PLA but with less slope.…”

“…The materials and methods for this study, as well as the conditions necessary to obtain both the pure components and their mixtures in c~-helix form, are described elsewhere [2]. Since, as is known [7], the collapse pressure and its kinetic behavior depends strongly on the velocity and on the modality of compression, particular care was taken in establishing and maintaining these conditions" the pressure-area isotherms were obtained in a discontinuous manner; the readings were made every 0.03 m/mg; the time interval between two successive readings was gradually increased from 5 to t0 rain in order to obtain a thermodynamic equilibrinm before each new compression, as has been done for other substances [4].…”

“…Previous works have demonstrated [1] monolayer compatibility at the water/air interface of two polypeptides with the same macromolecular conformation, especially in the a-helix [2,3] conformation. It has also been demonstrated [4] that the study of the collapse mechanism of mixed monolayers could provide information concerning the reciprocal miscibility of the components in condensed monolayers as well as in the collapsed phase.…”

“…The choice of these substances was justified because of their stability in bidimensional phases and because of the knowledge of the behavior of their bidimensional mixtures at the water/air interface under equilibrium conditions [2].…”

Mixed monolayers of polymethacrylic esters containing aromatic and aliphatic groups

“…The following equation was used Fig. Actual z values may be computed according to Singer theory [13] as described in previous works [14] but they appear to be useless in case of mixtures when strong approximations should be made to account for non-ideality. Joos' parameters and the interaction energies for all the mixtures at various temperatures were calculated, as in previous papers [12], from the relationship A-~kT ~kT z~--6 (2) zl = 6 in closely packed monolayers where zl and ~ are the interaction energy and interaction parameter respectively.…”