Stabilization of ferrochelatase via lysine residues on the carboxyl terminal extension.

There are accumulating evidences suggesting that ferrochelatase is involved in different cellular functions other than heme biosynthesis. The carboxyl-terminal extension of the enzyme may play a role associated with its stability and signaling process. Two transcript variants encoding different isoforms have been found for this ferrochelatase-coding gene. Variants encoding different isoforms have been found for this gene and were implicated in novel cellular activities including gene expression. Deficiency in ferrochelatase variants is believed to be associated with its stability. In this study, mutagenesis study of the lysine residues at 357, 360 and 365 was conducted. The relative change in activity by measurement of fluorescence intensity of the mutant enzyme revealed that K365L retained > 40% activity, while the mutant K365I retained 24% activity. Other mutants with K357S and K360Q showed little enzyme activity (< 4%). The change in the tryptophan fluorescence intensity after Guanidinium chloride-induced denaturation of the mutants indicated that the enzyme become unfolded under the assay condition. The K365L mutation suggests a structural role of tryptophan in the enzyme. The stability of the enzyme attributed to conservation of lysine residues in the C-terminal extension of the enzyme. The lysine and tryptophan residues serve as a structure determinant of ferrochelatase.