The effects of several nucleotides on the molecular state and catalytic activity of Thiobacillus novellus cytochrome c oxidase - ATP affects the oxidase uniquely

The catalytic activity and molecular aspects of Thiobacillus novellus cytpc hrome c oxidase were affected by ATP. The steady-state kinetics in the oxid ation of ferrocytochrome c by the oxidase varied with the presence or absen ce of ATP; the [S]-v curve of the reaction was sigmoid in the absence of AT P whereas it was a Michaelis-Menten-type hyperbola in the presence of 700 m u M ATP. The oxidase was a dimer of the minimal structural subunit consisti ng of one molecule each of two subunits in the presence of Tween 20 and in the absence of ATP. The dimer dissociated into monomers in the presence of 700 mu M ATP. The trough at 452 MI seen in the second derivative absorption spectrum of the CO compound of the oxidase in the absence of ATP, a charac teristic of the cytochrome a component of cytochrome aa(3), dissappeared in the presence of 700 mu M ATP. However, ADP, AMP, GTP, CTP and UTP had litt le affect on both the [S]-v curve and the molecular mass of the oxidase whe n used in place of ATP.