Kinetics of the decomposition of [2Fe–2S] ferredoxin from spinach: implications for iron bioavailability and nutritional status

The decomposition of spinach ferredoxin has been studied, at 37°C, in the presence of: buffer (pH 7.5); water; 0.01 M hydrochloric acid; and 0.01 M hydrochloric acid with pepsin enzyme (0.09, 0.19 and 0.38%). The hydrolysis of the protein appears to occur slowly in the presence of water alone, but is greatly accelerated by the addition of acid. This hydrolysis reaction is proposed to involve the denaturation of the protein chain to the extent that the [2Fe–2S] core is released from the protein. In the presence of 0.01 M HCl, total iron release occurs. Pepsin appears to then breakdown the peptide linkages within the apoprotein. UV–visible spectroscopy has demonstrated a two stage reaction with loss of the peak at 422 nm correlating with breakdown and loss of the [2Fe–2S] cluster, and loss of the peak at 277 nm demonstrating breakdown of the protein chain. Uniphasic kinetics were observed at 422 nm with the observed pseudo-first order rate constant having a linear dependence on ferredoxin concentration.