Lipid mediators enzymatic processes

FIGURE 9.1 Common enzymatic processes involved in the formation of anti-inflammatory and pro-resolving lipid mediators from PUFA. (a) Selective release of PUFA catalyzed by cytosolic phospholipase A2 (b) Stereocontrolled oxygenation of PUFA mediated by oxygenase enzymes (COX2/aspirin, P450, 5-LO, 15-LO), followed by peroxidases and epoxide hydrolases. 

Hydrolysis is an enzymatically mediated multistep process by which primary fermenting bacteria break down complex polymeric substances such as polysaccharides, carbohydrates, lipids, proteins, and nucleic acids, into monomers such as amino acids, long-chain fatty acids, glycerol, purines, etc. The enzymes required to carry out the process can be either attached to the microbial cell (Tong and McCarty 1991 Tong and McCarty 1991) or released into the bulk liquid by primary... 

The absorption efficiency of the different carotenoids is variable. For example, (3-cryptoxanthin has been reported to have higher absorption efficiency than a-cryptoxanthin in rats (Breithaupt and others 2007). Carotenoids must be liberated from the food before they can be absorbed by intestinal cells (Faulks and Southon 2005). Mechanical disruption of the food by mastication, ingestion, and mixing leads to carotenoid liberation (Guyton and Hall 2001). The enzymatic and acid-mediated hydrolysis of carbohydrates, lipids, and proteins (chemical breaking of the food) also contributes to carotenoids liberation from the food matrix (Faulks and Southon 2005). Once released, carotenoids must be dissolved in oil droplets, which are emulsified with the aqueous components of the chyme. When these oil droplets are mixed with bile in the small intestine, their size is reduced, facilitating the hydrolytic processing of lipids by the pancreatic enzymes (Pasquier and others 1996 Furr and Clark 1997 ... 

Special tasks. Some lipids have adopted special roles in the body. Steroids, eicosanoids, and some metabolites of phospholipids have signaling functions. They serve as hormones, mediators, and second messengers (see p.370). Other lipids form anchors to attach proteins to membranes (see p.214). The lipids also produce cofactors for enzymatic reactions—e.g., vitamin K (see p.52) and ubiquinone (see p.l04). The carotenoid retinal, a light-sensitive lipid, is of central importance in the process of vision (see p.358). 

Ketorolac is not a 2-APA NSAID but rather a chiral arylalkanoic NSAID. A small amount 7%) of S to R inversion of ketorolac is evident in both rats and humans, and a more extensive amount of inversion (> 50%) occurs bidirectionally in the mouse [72,118]. The inversion of ketorolac appears to be enzymatically mediated, as ketorolac adenylate conjugates have been detected in rat liver homogenates and mitochondria. Interestingly, this inversion process was demonstrated to occur without formation of a CoA thioester conjugate as an intermediate, and no lipid incorporation occurred in mice [118-120]. 

The cellular uptake and release of glucose and other monosaccharides is a protein-mediated process. Such proteins are embedded into the cell membrane and can be regarded as hydrophilic pores within the hydrophobic lipid bilayer. Monosaccharide transporters are substrate specific and stereospecific their action is saturable and can be inhibited by specific competitors. Like an enzymatic reaction, the kinetic characteristics can be described by affinity constants and the number of transporter protein molecules determines maximal transport velocity (Vmax)-... 

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