RT Journal Article SR Electronic(1) A1 Poole, Robert K. A1 Scott, Robert I. A1 Chance, BrittonYR 1981 T1 The Light-reversible Binding of Carbon Monoxide to Cytochrome a1 in Escherichia coli K12 JF Microbiology, VO 125 IS 2 SP 431 OP 438 DO https://doi.org/10.1099/00221287-125-2-431 PB Microbiology Society, SN 1465-2080, AB Difference spectra at 77 K of intact Escherichia coli K12 grown under oxygen-limited conditions revealed the presence of cytochrome a 1. In the presence of CO, the band of the reduced form, observed in both the α and λ regions of the spectrum, was decreased. Dualwavelength scanning spectrophotometry at sub-zero temperatures revealed a flash-dissociable CO-binding pigment with a broad band around 595 nm, identified as cytochrome a 1 Photolysis in the presence of O2 revealed no such band in difference spectra where the reference spectrum was that of the CO-liganded form, a result consistent with the binding of O2 to cytochrome a 1. Repeated cycles of photolysis and recombination of the cytochrome with CO were demonstrated at −46 °C. The apparent energy of activation for the reaction with CO was 10·9 kcal mol−1 (45·6 kJ mol−1). The results are discussed in relation to previous assumptions and results regarding ligand binding to cytochrome a 1 and the function of this cytochrome in bacterial respiration., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-125-2-431