 below 3600 Dalton (unit)s. Further studies by Schiffmann and colleges found that cultures of growing Escherichia coli released oligopeptides of between 150 and 1500 daltons that appeared to have a free Carboxylic acid group but not a free Amine group.Given these clues and knowledge that bacteria transcribe (see Transcription (genetics)) proteins starting with "N"-formylmethionine whereas eukaryotic cells mostly initiate protein synthesis with non-formylated methionine, Schiffmann, Corcoran, and Wahl theorized and then showed that "N"-formyl-methionine and a series "N"-formyl-methionyl dipeptides and tripeptides stimulated the chemotaxis of neutrophils isolated from rabbit peritoneal exudates as well as of macrophages isolated from guinea pig peritoneal exudates.In further studies of various "N"-formylated oligopeptides, fMLF proved the most potent in stimulating rabbit neutrophil chemotaxis.