Effect of Detergents on the Utilization of Sphingomyelin by Brain Sphingomyelinases

Abstract

Complex lipids belonging to the group classified as “insoluble, swelling amphiphilic lipids” (1) form multibilayered liposomes when dispersed in aqueous media. These large aggregates are generally poor substrates for enzymatic utilization and, for interaction with suitable enzymes must be further dispersed or “solubilized”. This is usually done with the aid of a detergent (reviewed in ref. 2), although some success was obtained with sonicated, single-bilayered liposomes (e.g., 3). The exact nature of the effect, by the detergent that facilitates the interaction with the enzyme is still rather obscure. For numerous enzymatic reactions a nonionic detergent (e.g., Triton X-100) * or an anionic detergent (e.g., sodium dodecylsulfate or bile salts) was used; in some cases detergent mixtures were employed (2). It is generally assumed that the detergent exerts its beneficiary action by solubilizing the substrate. However, with some enzymes that utilize lipid substrates, a detergent enhanced reaction rates even when using a non-lipid, water-soluble substrate (e.g., (β-glucosidase using p-nitrophenyl glucoside (4) or methyl umbiliferyl glucoside (5). In such a case the detergent most probably affects the enzyme rather than the substrate. It is self-evident that if a lipid substrate (e.g., glucosyl-ceramide) is the substrate for the same enzyme, the detergent also solubilizes the substrate further to its affecting the enzyme.