Chemical activity of simple basic peptides.

Alternating all-L poly(leucyl-lysyl) increases markedly the rate of hydrolysis of oligoribonucleotides. Pure D poly (leucyl-lysyl) is as active as the all-L polymer. The homochiral polypeptides adopt a beta-sheet structure when complexed to the oligonucleotides. Alternating poly(D,L-Leu-D,L-Lys) made of racemic amino acids is much less efficient and is unable to adopt a beta-sheet structure. A set of alternating poly (leucyl-lysyl) ranging from the racemic to the homochiral all-L polymer has been checked. Their conformations can be described as a mixture of random coil and beta-sheet conformations, the amount of beta-sheet increasing with the optical purity of the polymer. The hydrolytic activity follows the proportion of beta-sheets, suggesting that the chemical activity is related to the geometry of the chain. Short peptides were prepared in order to evaluate the critical chain length required for the hydrolytic activity. A decapeptide is long enough to present 90% of the activity of the corresponding polypeptide.