Synthesis and characterization of poly(LysAla 3 )

The synthesis and characterization of poly(LysAla 3 ) are described. The polytetrapeptide is a model for short sequences found in proelastin, and is presumably involved in desmosine or isodesmosine cross‐link formation in the native protein. Poly(LysAla 3 ) is found to possess a mixture of conformations in aqueous solution dependent on molecular weight and pH. Low‐molecular‐weight (ca. 3000) material appears to be a mixture of random and extended helix at neutral pH. However, as the molecular weight is increased an increasing amount of α‐helix is observed rising to >50% for mol wt = 21,000. The α‐helical chain segments are thermally stable, melting to a mixture of extended and random forms at T m = 25°C. High pH (10.5) promotes further α‐helix formation but at pH >11.0 the polypeptide becomes insoluble. The inference is that short chain segments of the peptide in elastin are unlikely to be α‐helical in the equilibrium state but may fluctuate through such a conformation.