Coproporphyrinogenase in tobacco (Nicotiana tabacum L.)

[摘要]

1. Coproporphyrinogenase was extracted and purified from tobacco (Nicotiana tabacum L.). Enzyme activity was mainly located in mitochondria rather than in chloroplasts. The enzyme was purified by differential centrifugation, ammonium sulphate fractionation, calcium phosphate gel adsorption and dialysis. A 69-fold final purification was obtained. 2. An apparent K_m value of 3.6×10⁻⁵m was found, the value being largely dependent on the amount of coproporphyrin III recovered after reduction with sodium amalgam to coproporphyrinogen III. Protoporphyrin formation was linear up to 3h and decreased with further incubation. The enzyme activity increased with the concentration of enzyme protein up to 30μg/ml of solution. 3. Enzyme activity was greatly enhanced by increasing Fe²⁺ concentrations up to 0.5mm, beyond which inhibition occurred. Co²⁺ and Mn²⁺ were also found to activate at low concentrations (0.1mm) and inhibit at higher concentrations (5mm). Fe³⁺ and Cu²⁺, both at 0.1mm, and o-phenanthroline and EDTA, each at 1mm, were found to be inhibitory.