Use of Mutants to study the Electron Transport Pathway of Nitrate Reductase

NITRATE-INDUCIBLE TPNH (reduced triphosphopyridine nucleotide) cytochrome c reductase is believed to participate in nitrate reduction for the following reasons: (1) Sorger1 and Kinsky and McElroy2 showed that it is induced and repressed simultaneously with nitrate reductase by the same specific inducers and repressors. (2) Kinsky and McElroy2 observed that cytochrome c competes with nitrate in purified preparations of nitrate reductase. (3) These investigators also found that inhibitors of TPNH cytochrome c reductase inhibit nitrate reductase. (4) They further observed that the ratio of TPNH cytochrome c reductase to nitrate reductase remains constant throughout a fifty to seventy-fold purification by two procedures. (5) Sorger1,3 and Pateman et al.4 found that mutants at a single locus, lacking nitrate reductase, also lack nitrate-inducible TPNH cytochrome c reductase. (6) Sorger5 noted that the ratio of TPNH cytochrome c reductase to nitrate reductase remains constant during heat inactivation (at 31.1° C and 42.3° C) of crude extracts made from induced mycelium.