Chemically defined lipid concentrate

Figure 5.43 Phase contrast optical micrographs of typical helical structures in chemically defined lipid concentrate system, (a) Low-pitch helical ribbon with pitch angle i r = 11 2°. (b) High-pitch helical ribbons with pitch angle t t = 54 2°. (c) Intermediate-pitch helical ribbons with pitch angle i r = 40.8 3.8°. Reprinted with permission from Ref. 162. Copyright 1999 by the National Academy of Sciences, U.S.A.

In recent years most studies on oxidized phospholipids have been performed using mixtures of oxidation products that are generated from their polyunsaturated parent compounds like PA-PC or oxidized lipoprotein particles (e.g. oxLDL). These preparations contain a large variety of different substances differing in structure, polarity and hydrophobicity as well as bioavailability. In many of these oxidized lipid preparations, neither the type nor the content of the individual oxidized components was known. Therefore, the respective compounds contribute to the apparent biological activities of oxidized lipid mixtures to a different and unpredictable extent. Thus, it will be desirable to concentrate on chemically defined lipid species in the future. 

To standardize how enzyme activities are expressed, the Enzyme Commission of the lUB proposed that the unit of enzyme activity be defined as the quantity of enzyme that catalyzes the reaction of 1 pmol of substrate per minute and that this unit be termed the international unit (U). Catalytic concentration is to be expressed in terms of U/L or kU/L, whichever gives the more convenient numerical value. In this chapter, the symbol U is used to denote the international unit. In those instances in which there is some uncertainty about the exact nature of the substrate or when there is difficulty in calculating the number of micromoles reacting (as with macromolecules such as starch, protein, and complex lipids), the unit is to be expressed in terms of the chemical group or residue measured in following the reaction (e.g., glucose units, or amino acid units formed). 

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