Chemical Reagent Factory, China. E. coli DH 5α was
purchased from Beijing Dingguo Changsheng Biotechnology
Co., Ltd., China. Peptone and yeast extract were
purchased from OXOID Co. Ltd., UK. DCP was purchased
from Aldrich, USA. Solutions of potassium ferricyanide,
obtained from Sinopharm Chemical Reagent Beijing Co.,
Ltd., China, were made up fresh, wrapped in aluminum
foil and stored in the dark until use