Independent versus Cooperative Binding in Polyethylenimine–DNA
and Poly(l‑lysine)–DNA Polyplexes
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Abstract
The mechanism of polyethylenimine–DNA
and poly(l-lysine)–DNA complex formation at pH 5.2
and 7.4 was studied
by a time-resolved spectroscopic method. The formation of a polyplex
core was observed to be complete at approximately N/P = 2, at which
point nearly all DNA phosphate groups were bound by polymer amine
groups. The data were analyzed further both by an independent binding
model and by a cooperative model for multivalent ligand binding to
multisubunit substrate. At pH 5.2, the polyplex formation was cooperative
at all N/P ratios, whereas for pH 7.4 at N/P < 0.6 the polyplex
formation followed independent binding changing to cooperative binding
at higher N/Ps