The rates of deamidation in pH 7.5, 0.15 M, 37.0°C phosphate buffer of pentapeptide models of the sequences found near asparaginyl and glutaminyl residues in cytochrome c were measured. These rates were used to calculate a sequence‐determined half‐life for non‐deamidated cytochrome c. The sequence‐determined deamidation rates of the pentapeptide models were compared with the in vivo and in vitro deamidation rates of cytochrome c and the in vivo turnover rate of cytochrome c. Deamidation of the peptides during synthesis and purification was also measured. The implications of these measurements for deamidation as a biological molecular timer and deamidation during peptide synthesis are d