De-esterification of cholesteryl esters in human plasma alpha-lipoprotein (HDL) by preparations of staphylococcal alpha toxin.

Chemical extraction and analysis ofreaction mixtures of preparations of staphylococcal alpha toxin and human plasma ~-lipoproteln (HDL) indicated that the cholesteryl esters which form an integral part of the lipoprotein molecules were de-esterified by the toxin preparations with no apparent destruction of the cholesterol moiety° This report is the first of cholesterol esterase produced by staphylococcus. This activity is closely associated with alpha toxin and may be a manifestation of alpha toxin itself. In addition it is shown that soluble plasma lipoproteins are useful substrates for biological reactions involving lipids. Certain bacteria produce extracellular toxic proteins which are cytolytic, causing damage to the structural and functional integrity of membrane systems of eucaryotic and in some cases, procaryotic cells (I). The alpha toxin of Staphylococcus aureus is one such agent. It is a heat labile protein whose monomeric form has a sedimentation rate of 3S, which aggregates easily to a soluble, less active 12S form and eventually to an insoluble, inactive form (2). Although the secondary effects resulting from the action of alpha toxin on a variety of natural and artificial membrane systems have been described (3), the primary site and mechanism of membrane damage has not been reported. During investigations on the effect of membrane damaging agents on soluble lipoprotelns, I have obtained data indicating that preparations of staphylococcal alpha toxin had a specific action of de-esterlfying the cholesteryl esters which are an integral part of lipoproteln molecules (4)° The cholesteryl moiety itself does not seem to be altered by the toxin° Materials and Methods Alpha toxin, produced by the Wood 46 strain of Staphylococcus aureus was