Nickel transport in nickel-resistant strains ofNeurospora crassa

Abstract

Transport of Ni²⁺ has been studied in three Ni²⁺-resistant strains ofNeurospora crassa (Ni^R1, Ni^R3) and Ni^R3) and in the parent wild strainN. crassa Em 5297a. Several strainspecific differences have been found. Rates of Ni²⁺ uptake were Ni^R2>Ni^R1>Em>>Ni^R3. While K_m for Ni²⁺ uptake was similar, V_max values were sharply different, with Ni^R3 having the lowest value. Observed uptake was entirely due to transport into the intracellular phase. Transport was strongly pH dependent only in Em, Ni^R1, and Ni^R2, which had a pH optimum at 4; optimum was at pH 5 for Ni^R3. Mg²⁺ was powerfully inhibitory to Ni²⁺ uptake in Ni^R1 and Ni^R2, but was less efficient in Ni^R3; in contrast, Mn²⁺ was most inhibitory in Ni^R3. It has been suggested that Ni²⁺ resistance in Ni^R3 is specifically due to lowered levels of the Ni²⁺ transport system herein.