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 degreesC, i n 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 hydro lysis of the protein appears to occur slowly in the presence of water alone , but is greatly accelerated by the addition of acid. This hydrolysis react ion is proposed to involve the denaturation of the protein chain to the ext ent 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 th e peptide linkages within the apoprotein. UV-visible spectroscopy has demon strated a two stage reaction with loss of the peak at 422 nm correlating wi th 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 ob served at 422 nm with the observed pseudo-first order rate constant having a linear dependence on ferredoxin concentration. (C) 2001 Elsevier Science Ltd. All rights reserved.