The binding of DNA to water soluble carbodiimide modified proteins

Bovine serum albumin and human serum transferrin modified by the water soluble carbodiimides N-ethyl-N'-(3-dimethyl propylamino) carbodiimide (CDI) or N-ethyl-N'-(3-trimethyl propylammonium) carbodiimide (Me+CDI) to yield N-acylurea proteins bind pBR322 DNA reversibly showing electrostatic and non-electrostatic components in the binding energies (delta G overall). It is proposed that initially an electrostatic interaction arises from ion pair formation between the DNA phosphates and the N-acylurea entities. This is consolidated, in single stranded regions, by a second event in which it is suggested that the base guanine interacts with elements of the N-acylurea moieties through hydrogen bonding or a glyoxal-type addition.