43 by: Maddie Hubbard
Student : Maddie Hubbard
Enzyme: Lipoprotein Lipase
E.C. Number: 3.1.1.34
Enzyme Location – Lipoprotein lipase (LPL) is an extracellular enzyme found on the vascular endothelial surface that lines capillary walls within muscles and fatty tissue. The tissue that mainly contains these capillaries is adipose, heart, and skeletal tissue. LPLs are regulated by several factors, one of which is insulin. It is also activated by the cofactor apolipoprotein C-III (apoC-II).
Enzyme Function – Lipoprotein lipase plays an essential role in the metabolism and transport of lipids in the human body. Its main function is to catalyze the hydrolysis of the triacylglycerols (TAG) inside chylomicrons that circulate our bloodstream. Two classes of lipoprotein circulate the bloodstream; chylomicrons containing dietary triacylglycerols and fat-soluble vitamins as well as endogenously synthesized TAG that is secreted by the liver as very low-density lipoprotein (VLDL). These lipoproteins enter the bloodstream so that lipoprotein lipase can hydrolyze the TAGs and distribute the recovered fatty acids to tissues where it is stored. The chylomicrons that the TAGs were carried in shrink and the remnants are taken up by the liver. The cofactor apoC-II is necessary for maximal activity when catalyzing reactions. Without the use of the cofactor, LPL’s rate of catalysis is significantly reduced. ApoC-II is also carried in chylomicrons and VLDLs. This cofactor binds itself to the N-terminal region of the enzyme at Lys-147/Lys-148, assisting lipoproteins lipase in catalyzing the hydrolysis of TAGs. The other terminal of lipoprotein lipase is the C-terminal, which binds to the substrate.
Fun Facts – Abnormalities in LPL function can lead to multiple pathophysiological conditions, including atherosclerosis, chylomicronaemia, obesity, Alzheimer’s disease, and dyslipidaemia which is strongly connected to diabetes, insulin resistance, and infection. Having a deficiency or irregularity in LPL function can lead to a plethora of health issues related to the metabolism, transport, and function of fatty acids and lipids.
References:
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Mead, J., Irvine, S., & Ramji, D. (2002). Lipoprotein lipase: structure, function, regulation, and role in disease. Journal of Molecular Medicine, 80(12), 753–769. https://doi.org/10.1007/s00109-002-0384-9
Libretexts. (2022, February 28). N-Terminal. Chemistry LibreTexts. https://chem.libretexts.org/Ancillary_Materials/Reference/Organic_Chemistry_Glossary/N-Terminal
Pirahanchi, Y., Anoruo, M., & Sharma, S. (2023, July 30). Biochemistry, lipoprotein lipase. StatPearls – NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK537040/#:~:text=Lipoprotein%20lipase%20requires%20apolipoprotein-CII%2C%20a%20cofactor%20for%20lipoprotein,low-density%20lipoprotein%20and%20intermediate-density%20lipoproteins%20%28IDL%29%2C%20for%20activation.
Wu, S. A., Kersten, S., & Qi, L. (2020). Lipoprotein lipase and its Regulators: an unfolding story. Trends in Endocrinology and Metabolism, 32(1), 48–61. https://doi.org/10.1016/j.tem.2020.11.005
Information on EC 3.1.1.34 – lipoprotein lipase – BRENDA Enzyme Database. (n.d.). https://www.brenda-enzymes.org/enzyme.php?ecno=3.1.1.34#COFACTOR
Lipase – Proteopedia, life in 3D. (n.d.). https://proteopedia.org/wiki/index.php/Lipase