Ferric citrate reductase activity in laccaria laccata, an ectomycorrhizal fungus

Abstract

We have assessed iron acquisition by Laccaria laccata ATCC 42217 growing in defined medium with adequate levels of iron to support growth. A series of enzyme tests were conducted with mycelium to establish optimum conditions for ferric citrate reductase activity and to assess enzyme ihibition by divalent cations and by redox‐active metal oxyanions. Greatest reduction of ferric ion by these fungal cells was observed at pH 6.0 when NADH and FMN were added. Riboflavin was found to be a suitable replacement for FMN and NADPH can be used as a substitute for NADH. The apparent K_m for ferric citrate, NADH and FMN was 1.9 nMm, 0.4 μM and 0.1 MM, respectively. We observed that salts of Ni²⁺, Co²⁺, Cu²⁺, Zn²⁺, TeO₃ ²⁻, CrO₄ ²⁻, SeO₃ ²⁻ and SeO₄ ²⁻ inhibited the reduction of Fe³⁺ by the fungal cells.