Alkyl glycoside detergents: a simpler synthesis and their effects on kinetic and physical properties of cytochrome c oxidase.

Abstract

Octyl glucoside is an effective, nonionic, solubilizing agent for membrane proteins with the advantage of ease of removal by dialysis. In order to study the detergent-sensitive activity of cytochrome c oxidase, we chose this detergent because of its simple structure and the possibility of synthesizing analogues to test the structural dependence of the detergent specificity. A procedure was therefore developed that facilitates large-scale preparation of octyl glucoside and related alkyl glycosides, improving on previous methods by eliminating crystallization steps and employing a one-step purification of the final product on Dowex 1. This new purification procedure is particularly important for achieving the level of purity required to obtain the disaccharide, longer alkyl chain detergents in soluble form. Of the alkyl glycosides prepared (octyl beta-D-glucopyranoside, octyl beta-D-lactopyranoside, dodecyl beta-D-lactopyranoside, dodecyl beta-D-cellobiopyranoside, and dodecyl beta-D-maltopyranoside), lauryl (dodecyl) maltoside was found to be the most successful as an activator of purified beef and Neurospora cytochrome oxidase, giving two- to tenfold higher activities than octyl glucoside and other commercially available detergents, Tween-20 and Triton X-100. Kinetic studies using two different steady-state assay systems indicate that the activity changes are not the result of altered binding of the substrate but rather reflect a detergent effect on the state of association of the enzyme (as a monomer, dimer, or polymer) as well as on its intrinsic activity. By gel filtration procedures, lauryl maltoside and octyl glucoside were found to exist as monodisperse populations of micelles of 50 000 and 8000 daltons, respectively. The small uniform micelles and chemically well-defined structures of lauryl maltoside and octyl glucoside make them superior to other nonionic detergents for the study of membrane proteins in general and cytochrome oxidase in particular, since its activity in lauryl maltoside most closely approaches that of the physiological state.