title: Photodissociation of cytochrome oxidase-nitric oxide at low temperatures.
abstract: Spectrophotometric studies revealed the irreversible photodissociation of reduced cytochrome oxidase-nitric oxide (NO) at 5 K. The dissociated NO recombined as the sample temperature was raised, and the half-recombination temperature was 65 K. The photodissociation at 5K was also confirmed by a change in the EPR spectrum; that is, ferroheme a-NO signals at gx=2.09 and gm=2.006 were replaced by a new signal at gm=2.03, and this change was reversed at the temperature of liquid nitrogen. Comparison of such behavior with that of cytochrome oxidase-carbon monoxide led us to propose that on photodissociation of NO from heme iron, the NO was trapped specifically at a site near the heme iron producing a new paramagnetic species. Its identification will require further studies.
mesh_terms: D000818:Animals; D002417:Cattle; D055598:Chemical Phenomena; D002621:Chemistry; D003080:Cold Temperature; D004578:Electron Spin Resonance Spectroscopy; D003576:Electron Transport Complex IV / Q000528:radiation effects*; D008027:Light; D009569:Nitric Oxide / Q000528:radiation effects*; D010084:Oxidation-Reduction; D013057:Spectrum Analysis
chemical_list: D009569:Nitric Oxide; D003576:Electron Transport Complex IV