Molecular dynamics simulations of N-terminal peptides from apo-myoglobin with several lengths were executed to study their stability to testify the possibility of cotranslational folding. By analyzing 10 us MD simulations in water, we found that the secondary and tertiary structures of a short N-terminal peptide (36 residues) are unstable whereas those of longer N-terminal peptides (snore than 77 residues) are relatively stable. In addition, we confirmed that the structural changes are driven by the free energy. Our results suggest that a nascent apo-myoglobin chain starts to form a-helix structures after elongation of at least 77 amino acid residues. (c) 2006 Elsevier B.V. All rights reserved.