Lipoprotein co-factor

Lipase was first isolated from skim milk and characterized by Fox and Tarassuk in 1967. The enzyme was optimally active at pH 9.2 and 37°C and found to be a serine enzyme (inactivated by organophosphates). A lipoprotein lipase (LPL activated by lipoprotein co-factors) was demonstrated in milk by Korn in 1962 and was isolated by Egelrud and Olivecrona in 1972. LPL is, in fact, the principal indigenous lipase in milk and most recent work has been focused accordingly. The molecule has been characterized at the molecular, genetic, enzymatic and physiological levels (see Olivecrona et al, 1992). 

Snellman, Sylven and Jul n have isolated what appears to be the plasma co-factor from tissue, mast-cell cytoplasm. The co-factor was a lipoprotein containing lecithin, cholesterol, and neutral fats, together with a low molecular-weight polypeptide. Only the six amino acids cysteine, threonine, tyrosine, glycine, leucine, and tryptophan were present in the polypeptide. 

Heparin inhibits blood coagulation both in vivo and in vitro. In combination with a co-factor, antithrombin III, heparin interferes with several steps in the coagulation process. Furthermore, heparin activates lipoprotein-lipase, which splits triglycerides into free fatty acids and glycerol. 

After entry in the blood stream the chylomicrons are hydrolyzed by the endothelial-bound lipoprotein lipase with apo C-I as a co-factor, allowing the delivery of free FAs to muscle and adipose tissue. The chylomicron remnants are rapidly taken up into the liver via especial receptor. ApoE is the moiety required for rapid hepatic removal. Its activity is inhibited by C apolipoproteins, especially apoC-I. The liver utilizes the exogenous fat and can release surplus lipids via VLDL into the blood. The VLDL is another substrate for lipoprotein lipase. The remaining VLDL remnants can either be taken up into the liver or are hydrolyzed to LDL. These last delivers cholesterol to all body cells via its receptor [136]. Moreover other type of lipoprotein denominated as high-density protein (HDL) is an important scavenger of surplus cholesterol transporting it from cell membranes to the liver, where it is degraded or converted into biliary salts, an then eliminated by the entero-hepatic cycle [137]. 

Heber and co-workers (160) evaluated diets enriched in palm oil, coconut oil, or hydrogenated soybean oil for three 3-week test periods in healthy American males. No significant changes in TC, LDL-C, or apolipoprotein AI or B were apparent following consumption of the pahn oil diet. They therefore concluded that enrichment of the diet of normal healthy individuals with palm oil does not increase cardiovascular risk factors related to lipids and lipoproteins. Truswell and co-workers (161) compared the effect of palm olein and canola oil on plasma lipids and reported that the mean 3% rise in TC on palm olein compared with a normal Australian diet was predominantly due to a 10% rise of HDL-C. 

The cause of the neurologic symptomatology is obscure. The co-occurrence of ataxia and atypical pigmentary retinitis is a feature in several other hereditary syndromes, so that a common pathogenesis is likely for both symptoms. Gai-TONDE (1963) has emphasized the importance of lipoproteins for the metabolism of the nervous system, but the causal relation of a-jS-lipoproteinemia and ataxic disturbance has not yet been elucidated. It is possible that there is a common factor essential for the normal structure and function of the nerve cell on one hand, and the production of j8-lipoproteins on the other (Salt et al. 1960), but it appears more likely that the lack of j8-lipoprotein formation actually represents the central lesion. 

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