substances including coenzymes which must be present in many eniymatic reactions, in their absence the enzymatic reaction cannot proceed) Thus apo I I

substances including coenzymes which must be present in many eniymatic reactions, in their absence the enzymatic reaction cannot proceed) Thus apo I is a cotactor of lecilhm cholesterol acyl transtecase (LCAT) ativity, CM acts as a cofactor for lipoprotein lipase activity Genetic absence of CM in a family causes the disease familial hypercholesTeremia (b) bin from the pom! of view of medical students the most important fact is that because of the presence of these apoli pop roleins, the hpoproteins can combine with their specific race plots of the largal cells (and subsequently metabolized) Thin apo B binds with LDL and the LDL now can bind with its receptor it is hightly possible that abnormalities of these of such diseases like atherosclerosis and hyperchotesteremia. Structure of a lipoprolein [NB To keep the discussion simple, only 4 classes of lipoproteins have been mentioned above Most authors now include IOL {intermediate density lipoprol em) in addition lo the above 4 categories) Upoprotem lipase. After a meal very rich in fat. the plasma becomes milky. This milkiness is due ret the presence of exces s amount of chylomicron particles In the plasma In due time, or following a heparin injection, the plasma is cleared of its milkiness. This clearing is due to the activity of a clearing factof (.an enzyme] called plasma lipoproiem hpate As a result or the action of this enzyme, the Inglycenda portion of the lipoprotein is hydrulyzed to glycerol and free fatty acids (FFA) Most of the FFA rhus formed enter the ertrahepatic tissues (like the muscles, where they are catabolized) This causes clearing of the plasma. The anginal chylomrcron panicle therefore now becomes much smaller, and contains tha protein cholesterol and phospholipid portions but practically no Inglyceride. The small remnants of chylomicron* particles now go to liver where they will be further catabulued. The enzyme lipoprotir irpase (clearing factor lipast) is present in the walls of the capillaries of blood and therefore present in sufficient amount in large number of organs which 31 e rich in capillaries. This enzyme is different from (and therefore should not be confused with) the adipose tissue (also called, hormone sensitive") hpase Hepann injection causes release of the plasma hpoprorem lipase from the endothehal cells of capillary walls [Hepann also causes release of another hpase. from The liver, called, heparin releasable hepatic Ijpcprolem It-past, whose function is largely obscure] Applied biochemistry of plasma hpoproteins Disorders of lipid metabolism and lipoproieint Many disorders of lipid metabolism an aitociatid with changes of plasma lipoproteina. Thus atherosclerosis/ coronary heart diseases (CHD) are associated with changes of plasma lipid values as well as llpoprotem pattern, changes include increase of plasma cholesierol values (hypercholesteremia) and rise of p llpoprotem ((JLP) Further, in atheroscleiosis the ratio of pLP/ a LP increses. This 19 underslandable, inspection of Tsble 7 t2 will show that most of the cholesterol is present in the aLP (= LDL) fraction of The hpoproletns Kamholesma is also assoculpd with increase of pLP Idiopalhic
'hyperlipemia. diabetes mellitus. myixedema. nephrotic syndrome are also characterized by rise of plasma hpid values Importance of lipoproiem estimation in diseases in the late 1950s and 60s it began to be suspected strongly that for diagnostic (as well as prognostic) purposes in disorders of lipid metabolism (atheraselerosis. xantholesma. Thanhauser's disease etc J over and above the estimation of plasma cholesterol and triglycendes, estimation of plasma lipoproleins is also imptrative it was suggested N B (i) Sf = Svedberg's ftotation unit Higher the Sf value greater is tha tendency to float in the solution (a) Some authors recognize two furthtr vanties, (a) chylormcron remnants (s*« fool note previous page), (b) IDL, in between LDL and VLDL that value of plasma cnuTesierol may remain almost normal but the ratio of p LP/ a LP might increase. However, now it is usually conceded lhat for routine clinical purposes, estimation of serum (or plasma) cholesterol and Inglycende is reasonably enough, lipoproiem estimation does not give much additional informations. Rectnrly however, estimation of the different types of apohpoprotein, for predicting the possibility of CHD. is becoming popular Further, it is now agreed that persons who have a high cholesterol HDL ratio are specialty prone id atheraseter-asis. Therefore, like smoking, obesily. drabetes and hypertension, bad cholesterol HDL ratio is also a risk factor Free tally acids. The FFA accounts for about 5% of the lotal plasma lipids But because of the exlremely rapid lumover rate, this is a very important sechon of
.plasma lipids FFA in plasma remains bound with plasma albumin (and thus becomes soluble} Within the cells, There is a protein called Z protein (also called. fatty acid binding protein), which binda with the FFA Z protein is thus.tha caunltrpvt of albumin. Fatlora influencing plasma lipid valuta. A Hormones Insulin reduces plasma lipid values (Old standing diabetics nave sometimes abnomially high values of plasma Lipids which however may not always be controlled by insulin and diet control (sec chap 7. 9, diabetes and lipid merabolism)insulin promotes fatty acid synthesis by stimulating HMP which causes
generation of NAOPH. and the H atoms of NADPH can subsequently be utilzed for fitly acid synthesis. Insulin inhibits
inhibiting hormone sensitive Ijpoprolein hpase m adipose tissue and Thus Ihe FFA co