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This paper by Alfred G. Hildebrandt and Ronald W. Estabrook at the University of Texas (Southwestern) Medical School, led to the concept of cytochrome b(5) (b(5)) as an auxiliary protein facilitating some cytochrome P450 (P450) reactions in the liver and other tissues. The gist of the paper is that DPNH (now known as NADH) enhanced rates of TPNH (now NADPH)-supported N-demethylation of O-ethylmorphine in rat liver microsomes. The conclusion was that b(5) was providing an electron to the ferrous-oxy form of P450 (Fe(2+)O(2)), which was supported by some spectral observations on the oxidation state of b(5) in the microsomes in the steady state. This observation led to a flurry of activity, which is still in progress. This paper has been cited 678 times in Google (558 in Clarivate), and I have often cited it myself. A PubMed search for the terms P450 and b(5) yielded 2,244 results.