Helix-Coil Transition in Synthetic Polypeptides and their IMM

2 Helix-Coil Transition in Synthetic Polypeptides and their IMM 

The changes in IMM during the conformational helix-coil transformation in synthetic polypeptides have also been studied by PL The polymer used was poly(glutamic acid) (PGA) with anthracene-containing luminescent markers in the side chains (one marker per 1000 monomer units). The structure and the position of the marker are  

The plots of I IP vs. (T/rj) at 25 °C for aqueous solutions of PGA at various pH in the range of the helix-coil transition are shown in Fig. 6. The lifetime of luminescence Tf was measured with a phase fluorometer. The values of the parameter of hi -frequency twisting vibrations of the marker I/P q are listed in Table 4 and the dependence of the IMM of PGA on pH is shown by the plot of t vs. pH (Fig. 7, curve 1). 

The change in the optical activity of PGA, the dependence of bo vs. pH (Fig. 7, curve 4) is an indication of the helix-coil transition. These data show that the breakdown of the a-helix in PGA is accompanied by a threefold increase in the IMM of the chain occurring cooperatively at the same pH at which bo (the fraction of a-helical sequences of PGA) changes. 

A comparison of (pH) and Te(pH) in relative units (t is the time describing the mobility of the chain end) suggests that during structure formation not only the mobility of the in-chain units of the polypeptide main chain changes but also the mobility of its end. 

The LM3 marker is an anthrylacyloxymethane group at the end of the side chain of the Glu unit (1 LM per 1000 monomer units) 

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