Abstract
The dissociation of beef liver and bacterial (Micrococcus lysodeikticus) catalases by the action of sodium nβdodecyl sulfate (SDS) has been investigated as a function of SDS concetration and time by ultracentrifugation. The rate of dissociation of beef liver catalase is found to be much faster than that for bacterial catalase in 25 m__M__ SDS at pH 7.0. Beef liver catalase is dissociated into its four subunits after 24 h, whereas bacterial catalase is not completely dissociated after 36 days of incubation. The binding of SDS to beef liver catalase obeys a Hill equation with a cooperativity exponent of 2.0 and a binding constant of 440. The initial interaction of SDS with beef liver catalase can be detected by microcalorimetry, whereas the mixing of SDS with bacterial catalase is athermal. Bacterial catalase retains enzymic activity in the presence of SDS, whereas beef liver catalase is completely deactivated at SDS concentrations above 5 m__M__. Beef liver catalase is more sensitive to acid denaturation than bacterial catalase, and the rate of dissociation for both catalases is sixthβorder in proton concentration. Comparison of the amino acid analysis of the two catalases shows that bacterial catalase has a smaller number of lysyl residues and a larger number of glutamyl residues than beef liver catalase. Taken together these structural differences could lead to a reduced affinity of bacterial catalase for the binding of SDS as observed.