Functional relationship between protein-bound and free factor F430 in Methanobacterium

Factor F430 is a nickel porphinoid present in all methanogenic bacteria. It is a component of methyl-CoM reductase to which it is tightly but not covalently bound. Evidence is presented that in Methanobacterium thermoautotrophicum grown on nickel sufficient medium only approximately 30% of total F430 is associated with methyl-CoM reductase and that 70% is present in a non-bound, free form. When such cells were transferred to a nickel deficient medium the bacteria continued to grow although synthesis of total F430 stopped. During growth in the absence of nickel the amount of total F430 per 1 culture remained constant and that per g cells decreased. The ratio of free F430 to bound F430, however, changed. Free F430 was converted into the protein-bound form until almost all of the free F430 had disappeared. The kinetics of labelling with 63Ni of free and bound F430 agreed rather well with that calculated for a precursor-product relationship between free and bound F430.