Clearing factor lipase

This enzyme [EC 3.1.1.34] (also called clearing factor lipase, diglyceride lipase, and diacylglycerol lipase) catalyzes the hydrolysis of a triacylglycerol to produce a diacylglycerol and a fatty acid anion. This enzyme hydrolyzes triacylglycerols in chylomicrons and in low-density lipoproteins and also acts on diacylglycerols. See also Lipases... 

Effect305 of Oral Sugars on Plasma Constituents and on Adipose-tissue, Clearing-factor, Lipase Activity in 24-Hour-Starved Rats... 

Substance administered Plasma concentration of Adipose-tissue, clearing-factor, lipase activity (units/g of fresh wt. of tissue)... 

Clearing factor lipase. Digiyceride lipase. Diacylglycerol lipase. Triacylglycerol + H(2)0 = diacylglycerol + a fatty acid anion. 

Wing, D. R., and D. S. Robinson. 1968. Clearing-factor lipase in adipose tissue. Biochem. J., 106 667. 

Metabolism of triacylglycerols in animals requires the interaction of lipoprotein lipase (involved in uptake of acyl chains from plasma) and hormone-sensitive lipase (involved in release of fatty acids from lipid stores). Some aspects of lipoprotein lipase action are discussed in Section 12.3 and the reader is also referred to Brockerhoff and Jensen (1974) and Jensen (1971). The enzyme is also known as clearing factor lipase, requires apo-Cn for activity and may be bound via heparan sulphate proteoglycan at the endothelial surface in vivo (Williams et aly 1983). Considerable work has been carried out on intracellular processing of the enzyme in active tissues (Cryer, 1981) and on the action of hormones in controlling the adipose and heart tissue enzymes (Ashby and Robinson, 1980 de Gasquet etaL, 1975). 

Clearing factor lipase (EC 3.1.1.3A) Hydrolysis of triacylglycerols in chylomicrons and VLDL... 

An enzyme with properties resembling those of the heparin-clearing factor lipase has been found in extracts of heart, adipose and other tissues (Korn 1955a Korn and Quigley 1957 Iselin and Schuler 1957). Perfusion of heparin through the circulation of many organs causes the liberation of clearing factor into the perfusate (Jeffries 1954 Robinson and Harris 1959 Swank and Levy 1952) while no activity is released from liver or brain. 

Robinson, D. S. The clearing factor lipase and its action in the transport of fatty acids between the blood and the tissues. Advanc. Lipid Res 1, 133—182 (1963). 

Heparin the clearing factor lipase and fat transport. Pharmacol. Rev. 12, 241 (1960). 

The Clearing Factor Lipase and Its Action in the Transport of Fatty... 

K5. Kom, E. D., Clearing factor, a heparin-activated lipoprotein lipase. II. Substrate specificity and activation of coconut oil. J. Biol. Chem. 215, 15-26 (1955). 

It is not intended to give a detailed account of the group of enzymes termed lipoprotein lipases or clearing factors, but during recent years so much attention has been focused on these enzymes that a review on lipases would not be complete without a summary of the present. state of knowledge of their properties. 

Lipoprotein lipases are so called because, unlike normal lipases, they do not hydrolyze, or hydrolyze very slowly, triglyceride emulsions, unless a lipoprotein complex is also present. The normal substrate is the turbid chylomicron-containing, or lipemic, plasma formed after a fatty meal. Since this substrate is clarified by the enzyme, the term clearing factor is used to describe a lipoprotein lipase. 

During the past few years, especially in view of the possible connection between lipid deposits in the aorta, atherosclerosis, and the clearing factor, much effort has been devoted to studies of the location of lipoprotein lipase in tissues, the possible identity of lipoprotein lipase with the clearing factor, and the physiological role of these enzymes. Many problems have yet to be solved. 

Within twenty seconds of injecting heparin into the femoral artery of a rabbit, blood samples of the femoral vein contained lipolytic activity. As this time is no greater than that required for the heparin to traverse the capillary bed of the hind Umb, this result indicates that the enzyme is readily accessible to heparin in the circulating blood (Robinson and Harris 1959). The enzyme is also found in the perfusate, when a heparin-serum albumin solution is perfused through an isolated hind limb. These findings led to the conclusion that the clearing factor is not present in the blood but is released into it by excessive doses of heparin. It is located in the capillary epithelium or on cell surfaces and its normal fimction is to act at these sites to facihtate transport of fat across the barriers. In accord with this concept is the distribution of lipoprotein lipase in the extrahepatic tissues, where an unmterrupted capillary epithelium exists and a special mechanism for fat transport is required. 

It is of particular interest to compare fluorine with other halogens or alkyl groups in order to confirm that fluorine mimics hydrogen. Comparison of the fluorine atom with the methyl group clearly indicates that the difference in van der Waals radii is an important factor in this lipase system. 

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