Studies on brain membrane-bound neuraminidase. II. Effect of detergents on the kinetics of the enzyme prepared from calf brain

Remodeling of sphingolipids by plasma membrane associated enzymes

The sphingolipid plasma membrane content and pattern is the result of several processes, among which the main, in term of quantity, are: neo-biosynthesis in endoplasmic reticulum and Golgi apparatus, membrane turnover with final catabolism in lysosomes and membrane shedding. In addition to this, past and recent data suggest that the head group of sphingolipids can be opportunely modified at the plasma membrane level, probably inside specific membrane lipid domains, by the action of enzymes involved in the sphingolipids metabolism, working directly at the cell surface. The number of membrane enzymes, hydrolases and transferases, acting on membrane sphingolipids is growing very rapidly. In this report we describe some properties of these enzymes.

GM1 ganglioside-Triton X-100 mixed micelles. Transitions among different micellar species monitored by physicochemical and enzymatic methods

Aqueous dispersions of two amphiphiles, GM1 ganglioside and Triton X-100, in different proportions, were analysed for some physicochemical properties (surface tension, viscosity, consolution temperature) and for susceptibility to the action of galactose oxidase. By varying the molar ratio between the two components, well defined transitions among different micellar species were recorded by physicochemical measurements. Galactose oxidase was able to recognize the different species of mixed micelles, its kinetics displayed break points which exactly superimposed on those recorded, under the same conditions, by physicochemical methods.

[Lipid-protein interactions: mechanisms of enzymatic glycolipid catabolism and their genetic restrictive escapes]

Investigations of the genetic basis of ganglioside catabolism have led to the characterisation of two types of lipid-enzyme interaction: a) Breakdown of membrane-bound glycolipids as far as catalysed by membrane-bound enzymes is regulated by the membrane itself. b) The degradation of micelle-forming glycolipids by water-soluble lysosomal enzymes is facilitated by cofactors known as activator proteins. A genetic defect in an activator protein can be just as fatal as the lack of the enzyme itself.