Cytochrome c (cyt c) is an evolutionarily conserved globularprotein often used as a model for studying the protein stability and folding. Although its role as an electron carrier in the electron transport chain is well documented, findings about its role as a protein that could trigger apoptosis upon its release from mitochondria have reignited interest in cyt c structure and function. We have studied the role of two alanine‐to‐cys mutants that were designed in the omega loop of the cytochrome c. The importance of this loop is evident from the finding that the only reported natural variants associated with disease in human cyt c are found in this loop. Also, in vitro studies have shown that mutations in this loop impact the apoptotic function of cyt c. Our DSC data suggests that the A44C and A51C mutants are less stable than the wild type protein. A44C being least stable while the A51C's stability being intermediate between A44C and the wild type, as judged by the decline in their Tm. Additionally, the preliminary results from the in vitro cell free caspase 3 activity assay indicate altered apoptotic activities of these mutants. Results from the secondary structure comparison using CD suggests that the secondary structure of these mutants is not changed much while a change in the tertiary structure is clearly evident. We propose that on mutating Ala to Cys at these locations a possible conformational change occurs which could facilitate the change in caspase activity while decreasing the overall stability of the protein.Support or Funding InformationThis work was supported in part by the Institute for Functional Nanomaterials (NSF Cooperative Agreement 1002410)