Q. Describe Lipoprotein?

Ans.

There is considerable current interest in this lipoprotein, which consists of LDL with an additional apoprotein-apoprotein (a) attached to it via a disulphide bond. Apoprotein (a) has striking structural homology with plasminogen, a zymogen of the coagulation and fibrinolytic system.

Lipoprotein (a) concentrations vary widely within and between populations. In Europeans most individuals have low levels but there is a pronounced positive skew to the distribution with very high levels in some people. The variation appears to be largely determined by the apoprotein (a) gene locus. Plasma concentrations correlate inversely with the molecular mass of apoprotein (a), which exists in many different size polymorphisms.

The physiology of lipoprotein (a) remains poorly understood but its rate of production appears to be a major determinant of its plasma concentration. It is likely that apoprotein (a) is directly secreted by the liver and then associates with LDL.

The importance of lipoprotein (a) relates to its association with CHD risk and, form its structural homology with plasminogen. It is tempting to speculate that this lipoprotein may be an important link with the coagulation system. Many case control studies have demonstrated that high lipoprotein (a) concentrations relate to CHD risk but the association appears to be influenced by the prevailing LDL concentration - the higher the LDL, the stronger the relationship between lipoprotein (a) and CHD.