THE HIGH-SPIN CYTOCHROME O' COMPONENT OF THE CYTOCHROME BE-TYPE QUINOL OXIDASE IN MEMBRANES FROM ESCHERICHIA-COLI - FORMATION OF THE PRIMARY OXYGENATED SPECIES AT LOW-TEMPERATURES IS CHARACTERIZED BY A SLOW ONRATE AND LOW DISSOCIATION-CONSTANT

Cytochromes b and o in membrane vesicles from aerobically grown Escher ichia coil were readily reduced by succinate; one cytochrome, which we propose should be called cytochrome o', reacted with CO in the Fe(II) state to give a photodissociable CO adduct. The photodissociation spe ctrum (photolysed minus pre-photolysis) at sub-zero temperatures had a relatively high gamma/alpha absorbance ratio, indicating a high-spin haem, which, in the reduced state, probably contributes little to the sharp a absorbance of the oxidase complex in membranes. Reaction with oxygen of the unliganded high-spin haem between -132 degrees C and -95 degrees C following photolytic activation gave a product that is iden tified as the oxygenated form, being spectrally similar to, but not id entical with, the CO adduct. In membranes, the forward velocity consta nt at -95 degrees C was 61 M(-1) s(-1), and the dissociation constant was 1.6 x 10(-5) M O-2, as it is in intact cells. These data clearly d istinguish the oxygen-trapping strategy of the cytochrome o' in this o xidase from that of cytochrome a(3) and also suggest that the presence of the soluble flavohaemoglobin (Hmp) in intact cells is without effe ct on such measurements of the primary oxygen reaction. In view of rec ent findings that this oxidase complex contains predominantly one mole of haem O and one of haem B. a revised nomenclature for the oxidase c omplex is proposed, namely, cytochrome bo'.