Sphingolipids substrates

A simple and inexpensive assay of the P-o-galactocerebrosidase from leucocytes relies on separation of the tritiated sphingolipid (substrate) from the tritiated hydrophobic product (ceramide) by t.l.c. on silica gel impregnated with sodium tetraborate. ... 

The enzymes involved in the synthesis of glycosphingolipids are cjh cosyl transferases, each specific for a particular sugar-nucleotid and acceptor. [Note These enzymes may recognize both glya sphingolipids and glycoproteins as substrates.]... 

Lipid rafts on cell membranes are cholesterol- and sphingolipid-rich domains that function as platforms for signal transduction and other cellular processes [6], Tethered lipid bilayers have been proposed as a promising model membrane to describe the structure and function of cell membratKs [7]. Based on these facts, we endeavor to array the lipid rafts as a form of tethered bilayer lipid membrare into the nanopattemed substrates to generate a raft membrane-based biosensing platform (Fig. Ic). 

Recent studies suggest that detergent-resistant subdomains of the plasma membrane ( rafts , discussed previously) may be involved in formation of PrP . Consistent with this idea, both PrP and PrP are found in raft domains isolated biochemically (Gorodinsky and Harris, 1995 Taraboulos et al, 1995 Naslavsky et al., 1996 Vey et al., 1996 Naslavsky et al., 1999). In addition, pharmacological depletion of cellular cholesterol, which is known to disrupt rafts, inhibits PrP formation (Taraboulos et al, 1995), whereas sphingolipid depletion, which does not alter the raft localization of PrP, actually enhances PrP production (Naslavsky et al, 1999). Finally, artificially constructed transmembrane forms of PrP, which are excluded from rafts, are poor substrates for conversion to PrP (Kaneko et al., 1997). 

The lysosomal hydrolysis of SM to Cer and phosphocholine is catalyzed by acid SMase, a water-soluble, lysosomal glycoprotein that interacts with a sphingolipid-activator protein (SAP) and anionic lipids such as bis(monoacylglycerol)phosphate (BMP) to hydrolyze interfacial SM (T. Linke, 2001). Acid SMase possesses an N-terminal SAP-homology domain that appears to stabilize the correctly folded form of acid SMase as well as to facilitate the interfacial interaction with substrate in vivo (M. Kolzer, 2004). Acidic SMase is also secreted by many types of cells (I. Tabas, 1999 I. Takahashi, 2005). 

Many of the above enzymes require detergents for optimal activity in vitro. Some workers have suggested that naturally occurring substances may be present in mammalian cells which could serve a similar function. It has also been postulated that the various sphingolipid hydrolases may also be aligned in an ordered fashion on lysosomal membranes. In that case hydrolysis of sphingolipids should be much more efficient than random access of various substrates to enzymes freely admixed within a lysosomal sac (Brady, 1978). 

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