The speed limit for protein folding measured by triplet-trlplet energy transfer

摘要

A direct measure of intramolecular chain dif fusion is obtained by the determination of triplet-triplet energy- tansfer rates between a donor and an acceptor chroinophore attached at defined points on a polypeptide chain. Singie expo- nenfial kinetics of contact formation are observed on the nano- arond time scale for polypeptides in which donor and acceptor are linked by repeating units of glycine and serine residues. The rates depend on the number of peptide bends (N) separating donor and acceptor and show a maxiinum for the shortest peptides (N = 3) with a time constant (t = 1/k) of 20 ns. This sets an upper limit for the speed of formation of the first side-chain contacts during protein folding.