Inhibition of cytochrome c oxidase by sulphide.

of the detergents used (Evans, 1956), although the sharp cut-off in activity evident lends support to the idea that protein denaturation by anionic detergents involves the formation of protein-detergent micelles (Tanford, 1970). The most effective inhibitor of glucuronidase activity was sodium tridecyl sulphate, whereas sodium pentadecyl sulphate exerted the strongest effects on the sulphatase. In the latter case, inhibition by CI6, CI7 and CIS alkyl sulphates was limited by the insolubilities of these detergents at the temperature used (37°C). With glucuronidase activity, complete inhibition was not evident even at the highest detergent concentration tested ( l o r n ) , suggesting the possibility of traces of resistant enzyme in the mixture; however, resolution of the crude enzyme mixture by gel filtration on Sephadex G-75 (Pharmacia, Uppsala, Sweden) revealed only a single peak of glucuronidase activity separated from two sulphatase activities. A noteworthy feature of the results relates to the effects of sodium pentadecyl sulphate on the two enzyme activities. At a concentration of 1 rn, inactivation of sulphatase by this detergent was complete, whereas glucuronidase activity remained unimpaired by concentrations as high as 10mM. Such a selective action suggests more general applications of sodium alkyl sulphates to problems associated with biochemical separations in that choice of a particular alkyl sulphate and its concentration may permit the irreversible inactivation of unwanted enzyme activities, leaving others unscathed. There may be possibilities here, too, in isoenzyme estimations. These studies also indicate that earlier observations suggesting a relationship between side-chain hydrophobicity and the effectiveness of anionic detergents in protein denaturation may need reconsideration and that the interactions between these detergents and proteins may be more specific than has been supposed.