Classification of Serum Lipoproteins According to Their Ultracentrifugal Characteristics

The presence of lipids within the lipoprotein particles confers these macromolecular complexes with a lower density compared with other serum proteins. With the arrival of the analytical ultracentrifugation in the 1940s, this characteristic allowed its initial separation as a discrete peak using this technique. During the following years, it was demonstrated that this fraction was made up of a wide spectrum of particle sizes and densities (d) ranging from 0.92 to 1.21 gml-1.

Lipoproteins were classically separated into four major classes designated as chylomicrons (exogenous triacylglycerol-rich particles of d <0.94 gml-1), very low-density lipoproteins (VLDL, endogenous triacyl-glycerol-rich particles of d = 0.94-1.006 g ml-1), LDL

(cholesteryl ester-rich particles of d = 1.0061.063 gml-1), and HDL (particles containing approximately 50% protein of d = 1.0631.21 g ml-1). With subsequent improvements to the ultracentrifugation techniques, further heterogeneity was detected within each of those major lipoprotein classes; this resulted in the need for further subdivision into several density subclasses such as HDL2a (d = 1.10-1.125gml-1), HDL2b (d = 1.063-1.10gml-1), and HDL3 (d = 1.125-1.21 gml-1).

There is no doubt that the separation of lipopro-teins by ultracentrifugation has been esential for the advances in this field; however, this technique is very labor intensive and the isolated lipoproteins are usually modified due to the high g force and salt concentrations used in this process. The development of new vertical and near vertical rotors has shortened considerably the runs and thus diminished some of these negative effects.

Breaking Bulimia

Breaking Bulimia

We have all been there: turning to the refrigerator if feeling lonely or bored or indulging in seconds or thirds if strained. But if you suffer from bulimia, the from time to time urge to overeat is more like an obsession.

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