Abstract
Stripped chloroplasts were prepared from young leaves of a tomato wild type (Lycopersicon esculentum Mill.) and its mutant chloronerva. Several morphological and biochemical abnormalities of this mutant are caused by the total lack of the plant-endogenous Fe 2+ chelator nicotianamine (NA). The ferrochelatase activity was estimated by determination of 59 Fe incorporated into haem. A mercaptoethanol concentration of 250 mM was necessary to maintain full enzyme activity. The reducing agent supported the reduced state of the active site of the enzyme more than that of the iron as revealed by use of ferrous and ferric ion-providing compounds as substrates. Chloroplasts of both genotypes exhibited a similar enzyme activity. NA inhibited this activity by nearly 100% depending on the concentration applied. On the basis of the formation constant of the Fe(ll)-NA complex and the concentrations of iron and NA in the enzyme assay as well as in the tomato shoot apex region it is proposed that ferrochelatase acts in vivo with an iron level at the attomolar range which is provided by NA.
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