During the 1950s, linear and multichain poly-a-amino acids were synthesized by polymerization of the corresponding N-carboxy-amino acid anhydrides in solution in the presence of suitable catalysts. The resulting homo- and heteropolymers have since been widely employed as simple protein models. Under appropriate conditions, poly-a-amino acids, in the solid state and in solution, were found to acquire conformations of an a-helix and of (^-parallel and antiparallel pleated sheets, or to exist as random coils. Their use in experimental and theoretical investigations of helix-coil transitions helped to shed new light on the mechanisms involved in protein denaturation. Poly-a-amino acids played an important role in the deciphering of the genetic code. In addition, analysis of the antigenicity of poly-a-amino acids led to the elucidation of the factors determining the antigenicity of proteins and peptides. Interest in the biological and physicochemical characteristics of poly-a-amino acids was recently renewed because of the reported novel findings that some copolymers of amino acids are effective as drugs in multiple sclerosis, and that glutamine repeats and reiteration of other amino acids occur in inherited neurodegenerative diseases. The presence of repeating sequences of amino acids in proteins, and of nucleotides in DNA, raises many interesting questions about their respective roles in determining protein structure and function, and gene performance and regulation.
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